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1 pgLatLon v0.3 documentation
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2 ===========================
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3
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4 pgLatLon is a spatial database extension for the PostgreSQL object-relational
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5 database management system providing geographic data types and spatial indexing
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6 for the WGS-84 spheroid.
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7
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8 While many other spatial databases still use imprecise bounding boxes for many
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9 operations, pgLatLon aims to support more precise geometric calculations for
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10 all implemented operators. Efficient indexing of geometric objects is provided
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11 using space-filling fractal curves. Optimizations on bit level (including
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12 logarithmic compression) allow for a highly memory-efficient non-overlapping
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13 index suitable for huge datasets.
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14
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15 pgLatLon is a lightweight solution as it only depends on PostgreSQL itself (and
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16 a C compiler for building).
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17
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18 Unlike competing spatial extensions for PostgreSQL, pgLatLon is available under
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19 the permissive MIT/X11 license to avoid problems with viral licenses like the
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20 GPLv2/v3.
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21
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22
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23 Installation
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24 ------------
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25
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26 ### Automatic installation
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27
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28 Prerequisites:
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29
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30 * Ensure that the `pg_config` binary is in your path (shipped with PostgreSQL).
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31 * Ensure that GNU Make is available (either as `make` or `gmake`).
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32
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33 Then simply type:
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34
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35 make install
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36
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37 ### Manual installation
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38
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39 It is also possible to compile and install the extension without GNU Make as
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40 follows:
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41
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42 cc -Wall -O2 -fPIC -shared -I `pg_config --includedir-server` -o latlon-v0002.so latlon-v0002.c
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43 cp latlon-v0002.so `pg_config --pkglibdir`
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44 cp latlon.control `pg_config --sharedir`/extension/
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45 cp latlon--0.1--0.2.sql latlon--0.2.sql `pg_config --sharedir`/extension/
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46
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47 ### Loading the extension
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48
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49 After installation, you can create a database and load the extension as
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50 follows:
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51
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52 % createdb test_database
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53 % psql test_database
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54 psql (9.5.4)
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55 Type "help" for help.
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56
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57 test_database=# CREATE EXTENSION latlon;
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58
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59
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60 Reference
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61 ---------
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62
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63 ### 1. Types
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64
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65 pgLatLon provides four geographic types: `epoint`, `ebox`, `ecircle`, and
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66 `ecluster`.
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67
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68 #### `epoint`
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69
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70 A point on the earth spheroid (WGS-84).
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71
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72 The text input format is `'[N|S]<float> [E|W]<float>'`, where each float is in
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73 degrees. Note the required white space between the latitude and longitude
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74 components. Each floating point number may have a sign, in which case `N`/`S`
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75 or `E`/`W` are switched respectively (e.g. `E-5` is the same as `W5`).
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76
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77 An `epoint` may also be created from two floating point numbers by calling
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78 `epoint(latitude, longitude)`, where positive latitudes are used for the
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79 northern hemisphere, negative latitudes are used for the southern hemisphere,
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80 positive longitudes indicate positions east of the prime meridian, and negative
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81 longitudes indicate positions west of the prime meridian.
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82
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83 Latitudes exceeding -90 or +90 degrees are truncated to -90 or +90
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84 respectively, in which case a warning will be issued. Longitudes exceeding -180
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85 or +180 degrees will be converted to values between -180 and +180 (both
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86 inclusive) by adding or substracting a multiple of 360 degrees, in which case a
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87 notice will be issued.
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88
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89 If the latitude is -90 or +90 (south pole or north pole), a longitude value is
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90 still stored in the datum, and if a point is on the prime meridian or the
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91 180th meridian, the east/west bit is also stored in the datum. In case of the
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92 prime meridian, this is done by storing a floating point value of -0 for
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93 0 degrees west and a value of +0 for 0 degrees east. In case of the
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94 180th meridian, this is done by storing -180 or +180 respectively. The equality
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95 operator, however, returns true when the same points on earth are described,
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96 i.e. the longitude is ignored for the poles, and 180 degrees west is considered
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97 to be equal to 180 degrees east.
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98
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99 #### `ebox`
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100
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101 An area on earth demarcated by a southern and northern latitude, and a western
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102 and eastern longitude (all given in WGS-84).
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103
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104 The text input format is
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105 `'{N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float>'`, where each float is in
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106 degrees. The ordering of the four white-space separated blocks is not
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107 significant. To include the 180th meridian, one longitude boundary must be
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108 equal to or exceed `W180` or `E180`, e.g. `'N10 N20 E170 E190'`.
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109
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110 A special value is the empty area, denoted by the text represenation `'empty'`.
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111 Such an `ebox` does not contain any point.
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112
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113 An `ebox` may also be created from four floating point numbers by calling
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114 `ebox(min_latitude, max_latitude, min_longitude, max_longitude)`, where
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115 positive values are used for north and east, and negative values are used for
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116 south and west. If `min_latitude` is strictly greater than `max_latitude`, an
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117 empty `ebox` is created. If `min_longitude` is greater than `max_longitude` and
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118 if both longitudes are between -180 and +180 degrees, then the area oriented in
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119 such way that the 180th meridian is included.
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120
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121 If the longitude span is less than 120 degrees, an `ebox` may be alternatively
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122 created from two `epoints` in the following way: `ebox(epoint(lat1, lon1),
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123 epoint(lat2, lon2))`. In this case `lat1` and `lat2` as well as `lon1` and
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124 `lon2` can be swapped without any impact.
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125
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126 #### `ecircle`
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127
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128 An area containing all points not farther away from a given center point
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129 (WGS-84) than a given radius.
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130
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131 The text input format is `'{N|S}<float> {E|W}<float> <float>'`, where the first
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132 two floats denote the center point in degrees and the third float denotes the
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133 radius in meters. A radius equal to minus infinity denotes an empty circle
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134 which contains no point at all (despite having a center), while a radius equal
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135 to zero denotes a circle that includes a single point.
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136
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137 An `ecircle` may also be created by calling `ecircle(epoint(...), radius)` or
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138 from three floating point numbers by calling `ecircle(latitude, longitude,
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139 radius)`.
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140
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141 #### `ecluster`
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142
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143 A collection of points, paths, polygons, and outlines on the WGS-84 spheroid.
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144 Each path, polygon, or outline must cover a longitude range of less than
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145 180 degrees to avoid ambiguities.
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146
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147 The text input format is a white-space separated list of the following items:
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148
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149 * `point ({N|S}<float> {E|W}<float>)`
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150 * `path ({N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> ...)`
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151 * `outline ({N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> ...)`
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152 * `polygon ({N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> ...)`
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153
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154 Paths are open by default (i.e. there is no connection from the last point in
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155 the list to the first point in the list). Outlines and polygons, in contrast,
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156 are automatically closed (i.e. there is a line segment from the last point in
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157 the list to the first point in the list) which means the first point should not
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158 be repeated as last point in the list. Polygons are filled, outlines are not.
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159
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160 ### 2. Indices
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161
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162 Two kinds of indices are supported: B-tree and GiST indices.
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163
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164 #### B-tree indices
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165
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166 A B-tree index can be used for simple equality searches and is supported by the
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167 `epoint`, `ebox`, and `ecircle` data types. B-tree indices can not be used for
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168 geographic searches.
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169
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170 #### GiST indices
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171
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172 For geographic searches, GiST indices must be used. The `epoint`, `ecircle`,
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173 and `ecluster` data types support GiST indexing. A GiST index for geographic
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174 searches can be created as follows:
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175
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176 CREATE TABLE tbl (
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177 id serial4 PRIMARY KEY,
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178 loc epoint NOT NULL );
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179
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180 CREATE INDEX name_of_index ON tbl USING gist (loc);
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181
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182 GiST indices also support nearest neighbor searches when using the distance
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183 operator (`<->`) in the ORDER BY clause.
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184
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185 #### Indices on other data types (e.g. GeoJSON)
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186
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187 Note that further types can be indexed by using an index on an expression with
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188 a conversion function. One conversion function provided by pgLatLon is the
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189 `GeoJSON_to_ecluster(float8, float8, text)` function:
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190
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191 CREATE TABLE tbl (
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192 id serial4 PRIMARY KEY,
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193 loc jsonb NOT NULL );
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194
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195 CREATE INDEX name_of_index ON tbl USING gist((GeoJSON_to_ecluster("loc")));
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196
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197 When using the conversion function in an expression, the index will be used
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198 automatically:
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199
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200 SELECT * FROM tbl WHERE GeoJSON_to_ecluster("loc") && 'N50 E10 10000'::ecircle;
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201
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202 ### 3. Operators
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203
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204 #### Equality operator `=`
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205
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206 Tests if two geographic objects are equal.
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207
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208 The longitude is ignored for the poles, and 180 degrees west is considered to
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209 be equal to 180 degrees east.
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210
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211 For boxes and circles, two empty objects are considered equal. (Note that a
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212 circle is not empty if the radius is zero but only if it is negative infinity,
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213 i.e. smaller than zero.) Two circles with a positive infinite radius are also
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214 considered equal.
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215
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216 Implemented for:
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217
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218 * `epoint = epoint`
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219 * `ebox = ebox`
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220 * `ecircle = ecircle`
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221
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222 The negation is the inequality operator (`<>` or `!=`).
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223
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224 #### Linear ordering operators `<<<`, `<<<=`, `>>>=`, `>>>`
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225
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226 These operators create an arbitrary (but well-defined) linear ordering of
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227 geographic objects, which is used internally for B-tree indexing and merge
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228 joins. These operators will usually not be used by an application programmer.
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229
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230 #### Overlap operator `&&`
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231
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232 Tests if two geographic objects have at least one point in common. Currently
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233 implemented for:
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234
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235 * `epoint && ebox`
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236 * `epoint && ecircle`
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237 * `epoint && ecluster`
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238 * `ebox && ebox`
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239 * `ecircle && ecircle`
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240 * `ecircle && ecluster`
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241
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242 The `&&` operator is commutative, i.e. `a && b` is the same as `b && a`. Each
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243 commutation is supported as well.
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244
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245 #### Lossy overlap operator `&&+`
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246
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247 Tests if two geographic objects may have at least one point in common. Opposed
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248 to the `&&` operator, the `&&+` operator may return false positives and is
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249 currently implemented for:
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250
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251 * `epoint &&+ ecluster`
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252 * `ebox &&+ ecircle`
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253 * `ebox &&+ ecluster`
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254 * `ecircle &&+ ecluster`
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255 * `ecluster &&+ ecluster`
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256
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257 The `&&+` operator is commutative, i.e. `a &&+ b` is the same as `b &&+ a`. Each
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258 commutation is supported as well.
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259
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260 Where two data types support both the `&&` and the `&&+` operator, the `&&+`
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261 operator computes faster.
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262
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263 #### Distance operator `<->`
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264
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265 Calculates the shortest distance between two geographic objects in meters (zero
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266 if the objects are overlapping). Currently implemented for:
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267
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268 * `epoint <-> epoint`
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269 * `epoint <-> ecircle`
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270 * `epoint <-> ecluster`
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271 * `ecircle <-> ecircle`
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272 * `ecircle <-> ecluster`
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273
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274 The `<->` operator is commutative, i.e. `a <-> b` is the same as `b <-> a`.
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275 Each commutation is supported as well.
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276
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277 For short distances, the result is very accurate (i.e. respects the dimensions
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278 of the WGS-84 spheroid). For longer distances in the order of magnitude of
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279 earth's radius or greater, the value is only approximate (but the error is
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280 still less than 0.2% as long as no polygons with very long edges are involved).
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281
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282 The functions `distance(epoint, epoint)` and `distance(ecluster, epoint)` can
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283 be used as an alias for this operator.
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284
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285 Note: In case of radial searches with a fixed radius, this operator should
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286 not be used. Instead, an `ecircle` should be created and used in combination
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287 with the overlap operator (`&&`). Alternatively, the functions
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288 `distance_within(epoint, epoint, float8)` or `distance_within(ecluster, epoint,
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289 float8)` can be used for fixed-radius searches.
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290
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291 ### 4. Functions
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292
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293 #### `center(circle)`
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294
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295 Returns the center of an `ecircle` as an `epoint`.
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296
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jbe@0
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297 #### `distance(epoint, epoint)`
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298
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jbe@0
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299 Calculates the distance between two `epoint` datums in meters. This function is
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jbe@0
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300 an alias for the distance operator `<->`.
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jbe@0
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301
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jbe@0
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302 Note: In case of radial searches with a fixed radius, this function should not be
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jbe@0
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303 used. Use `distance_within(epoint, epoint, float8)` instead.
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jbe@0
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304
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jbe@0
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305 #### `distance(ecluster, epoint)`
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306
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jbe@0
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307 Calculates the distance from an `ecluster` to an `epoint` in meters. This
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jbe@0
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308 function is an alias for the distance operator `<->`.
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jbe@0
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309
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jbe@0
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310 Note: In case of radial searches with a fixed radius, this function should not be
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jbe@0
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311 used. Use `distance_within(epoint, epoint, float8)` instead.
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jbe@0
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312
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jbe@0
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313 #### `distance_within(`variable `epoint,` fixed `epoint,` radius `float8)`
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jbe@0
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314
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jbe@0
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315 Checks if the distance between two `epoint` datums is not greater than a given
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jbe@0
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316 value (search radius).
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jbe@0
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317
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jbe@0
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318 Note: In case of radial searches with a fixed radius, the first argument must
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jbe@0
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319 be used for the table column, while the second argument must be used for the
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320 search center. Otherwise an existing index cannot be used.
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321
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jbe@0
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322 #### `distance_within(`variable `ecluster,` fixed `epoint,` radius `float8)`
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jbe@0
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323
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jbe@0
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324 Checks if the distance from an `ecluster` to an `epoint` is not greater than a
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jbe@0
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325 given value (search radius).
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326
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jbe@0
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327 #### `ebox(`latmin `float8,` latmax `float8,` lonmin `float8,` lonmax `float8)`
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328
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jbe@0
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329 Creates a new `ebox` with the given boundaries.
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jbe@0
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330 See "1. Types", subsection `ebox` for details.
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331
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jbe@0
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332 #### `ebox(epoint, epoint)`
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333
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jbe@0
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334 Creates a new `ebox`. This function may only be used if the longitude
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jbe@0
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335 difference is less than or equal to 120 degrees.
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jbe@0
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336 See "1. Types", subsection `ebox` for details.
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337
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jbe@0
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338 #### `ecircle(epoint, float8)`
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jbe@0
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339
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jbe@0
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340 Creates an `ecircle` with the given center point and radius.
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jbe@0
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341
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jbe@0
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342 #### `ecircle(`latitude `float8,` longitude `float8,` radius `float8)`
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jbe@0
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343
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jbe@0
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344 Creates an `ecircle` with the given center point and radius.
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jbe@0
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345
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jbe@0
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346 #### `ecluster_concat(ecluster, ecluster)`
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jbe@0
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347
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jbe@0
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348 Combines two clusters to form a new `ecluster` by uniting all entries of both
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jbe@0
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349 clusters. Note that two overlapping areas of polygons annihilate each other
|
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jbe@0
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350 (which may be used to create polygons with holes).
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jbe@0
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351
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jbe@0
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352 #### `ecluster_concat(ecluster[])`
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jbe@0
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353
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jbe@0
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354 Creates a new `ecluster` that unites all entries of all clusters in the passed
|
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jbe@0
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355 array. Note that two overlapping areas of polygons annihilate each other (which
|
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jbe@0
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356 may be used to create polygons with holes).
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jbe@0
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357
|
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jbe@0
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358 #### `ecluster_create_multipoint(epoint[])`
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jbe@0
|
359
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jbe@0
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360 Creates a new `ecluster` which contains multiple points.
|
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jbe@0
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361
|
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jbe@0
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362 #### `ecluster_create_outline(epoint[])`
|
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jbe@0
|
363
|
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jbe@0
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364 Creates a new `ecluster` that is an outline given by the passed points.
|
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jbe@0
|
365
|
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jbe@0
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366 #### `ecluster_create_path(epoint[])`
|
|
jbe@0
|
367
|
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jbe@0
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368 Creates a new `ecluster` that is a path given by the passed points.
|
|
jbe@0
|
369
|
|
jbe@0
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370 #### `ecluster_create_polygon(epoint[])`
|
|
jbe@0
|
371
|
|
jbe@0
|
372 Creates a new `ecluster` that is a polygon given by the passed points.
|
|
jbe@0
|
373
|
|
jbe@0
|
374 #### `ecluster_extract_outlines(ecluster)`
|
|
jbe@0
|
375
|
|
jbe@0
|
376 Set-returning function that returns the outlines of an `ecluster` as `epoint[]`
|
|
jbe@0
|
377 rows.
|
|
jbe@0
|
378
|
|
jbe@0
|
379 #### `ecluster_extract_paths(ecluster)`
|
|
jbe@0
|
380
|
|
jbe@0
|
381 Set-returning function that returns the paths of an `ecluster` as `epoint[]`
|
|
jbe@0
|
382 rows.
|
|
jbe@0
|
383
|
|
jbe@0
|
384 #### `ecluster_extract_points(ecluster)`
|
|
jbe@0
|
385
|
|
jbe@0
|
386 Set-returning function that returns the points of an `ecluster` as `epoint`
|
|
jbe@0
|
387 rows.
|
|
jbe@0
|
388
|
|
jbe@0
|
389 #### `ecluster_extract_polygons(ecluster)`
|
|
jbe@0
|
390
|
|
jbe@0
|
391 Set-returning function that returns the polygons of an `ecluster` as `epoint[]`
|
|
jbe@0
|
392 rows.
|
|
jbe@0
|
393
|
|
jbe@0
|
394 #### `empty_ebox`()
|
|
jbe@0
|
395
|
|
jbe@0
|
396 Returns the empty `ebox`.
|
|
jbe@0
|
397 See "1. Types", subsection `ebox` for details.
|
|
jbe@0
|
398
|
|
jbe@0
|
399 #### `epoint(`latitude `float8,` longitude `float8)`
|
|
jbe@0
|
400
|
|
jbe@0
|
401 Returns an `epoint` with the given latitude and longitude.
|
|
jbe@0
|
402
|
|
jbe@0
|
403 #### `epoint_latlon(`latitude `float8,` longitude `float8)`
|
|
jbe@0
|
404
|
|
jbe@0
|
405 Alias for `epoint(float8, float8)`.
|
|
jbe@0
|
406
|
|
jbe@0
|
407 #### `epoint_lonlat(`longitude `float8,` latitude `float8)`
|
|
jbe@0
|
408
|
|
jbe@0
|
409 Same as `epoint(float8, float8)` but with arguments reversed.
|
|
jbe@0
|
410
|
|
jbe@0
|
411 #### `GeoJSON_to_epoint(jsonb, text)`
|
|
jbe@0
|
412
|
|
jbe@0
|
413 Maps a GeoJSON object of type "Point" or "Feature" (which contains a
|
|
jbe@0
|
414 "Point") to an `epoint` datum. For any other JSON objects, NULL is returned.
|
|
jbe@0
|
415
|
|
jbe@0
|
416 The second parameter (which defaults to `epoint_lonlat`) may be set to a name
|
|
jbe@0
|
417 of a conversion function that transforms two coordinates (two `float8`
|
|
jbe@0
|
418 parameters) to an `epoint`.
|
|
jbe@0
|
419
|
|
jbe@0
|
420 #### `GeoJSON_to_ecluster(jsonb, text)`
|
|
jbe@0
|
421
|
|
jbe@0
|
422 Maps a (valid) GeoJSON object to an `ecluster`. Note that this function
|
|
jbe@0
|
423 does not check whether the JSONB object is a valid GeoJSON object.
|
|
jbe@0
|
424
|
|
jbe@0
|
425 The second parameter (which defaults to `epoint_lonlat`) may be set to a name
|
|
jbe@0
|
426 of a conversion function that transforms two coordinates (two `float8`
|
|
jbe@0
|
427 parameters) to an `epoint`.
|
|
jbe@0
|
428
|
|
jbe@0
|
429 #### `max_latitude(ebox)`
|
|
jbe@0
|
430
|
|
jbe@0
|
431 Returns the northern boundary of a given `ebox` in degrees between -90 and +90.
|
|
jbe@0
|
432
|
|
jbe@0
|
433 #### `max_longitude(ebox)`
|
|
jbe@0
|
434
|
|
jbe@0
|
435 Returns the eastern boundary of a given `ebox` in degrees between -180 and +180
|
|
jbe@0
|
436 (both inclusive).
|
|
jbe@0
|
437
|
|
jbe@0
|
438 #### `min_latitude(ebox)`
|
|
jbe@0
|
439
|
|
jbe@0
|
440 Returns the southern boundary of a given `ebox` in degrees between -90 and +90.
|
|
jbe@0
|
441
|
|
jbe@0
|
442 #### `min_longitude(ebox)`
|
|
jbe@0
|
443
|
|
jbe@0
|
444 Returns the western boundary of a given `ebox` in degrees between -180 and +180
|
|
jbe@0
|
445 (both inclusive).
|
|
jbe@0
|
446
|
|
jbe@0
|
447 #### `latitude(epoint)`
|
|
jbe@0
|
448
|
|
jbe@0
|
449 Returns the latitude value of an `epoint` in degrees between -90 and +90.
|
|
jbe@0
|
450
|
|
jbe@0
|
451 #### `longitude(epoint)`
|
|
jbe@0
|
452
|
|
jbe@0
|
453 Returns the longitude value of an `epoint` in degrees between -180 and +180
|
|
jbe@0
|
454 (both inclusive).
|
|
jbe@0
|
455
|
|
jbe@0
|
456 #### `radius(ecircle)`
|
|
jbe@0
|
457
|
|
jbe@0
|
458 Returns the radius of an `ecircle` in meters.
|
|
jbe@0
|
459
|