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1 pgLatLon v0.1 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 supports more precise geometric calculations for all
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10 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 Unlike competing spatial extensions for PostgreSQL, pgLatLon is available under
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16 the permissive MIT/X11 license to avoid problems with viral licenses like the
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17 GPLv2/v3.
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18
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19
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20 Installation
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21 ------------
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22
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23 ### Automatic installation
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24
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25 Prerequisites:
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26
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27 * Ensure that the `pg_config` binary is in your path (shipped with PostgreSQL).
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28 * Ensure that GNU Make is available (either as `make` or `gmake`).
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29
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30 Then simply type:
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31
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32 make install
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33
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34 ### Manual installation
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35
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36 It is also possible to compile and install the extension without GNU Make as
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37 follows:
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38
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39 cc -Wall -O2 -fPIC -shared -I `pg_config --includedir-server` -o latlon-v0001.so latlon-v0001.c
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40 cp latlon-v0001.so `pg_config --pkglibdir`
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41 cp latlon.control `pg_config --sharedir`/extension/
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42 cp latlon--0.1.sql `pg_config --sharedir`/extension/
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43
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44 ### Loading the extension
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45
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46 After installation, you can create a database and load the extension as
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47 follows:
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48
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49 % createdb test_database
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50 % psql test_database
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51 psql (9.5.4)
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52 Type "help" for help.
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53
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54 test_database=# CREATE EXTENSION latlon;
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55
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56
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57 Reference
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58 ---------
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59
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60 ### 1. Types
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61
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62 pgLatLon provides four geographic types: `epoint`, `ebox`, `ecircle`, and
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63 `ecluster`.
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64
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65 #### `epoint`
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66
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67 A point on the earth spheroid (WGS-84).
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68
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69 The text input format is `'[N|S]<float> [E|W]<float>'`, where each float is in
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70 degrees. Note the required white space between the latitude and longitude
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71 components. Each floating point number may have a sign, in which case `N`/`S`
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72 or `E`/`W` are switched respectively (e.g. `E-5` is the same as `W5`).
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73
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74 An `epoint` may also be created from two floating point numbers by calling
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75 `epoint(latitude, longitude)`, where positive latitudes are used for the
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76 northern hemisphere, negative latitudes are used for the southern hemisphere,
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77 positive longitudes indicate positions east of the prime meridian, and negative
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78 longitudes indicate positions west of the prime meridian.
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79
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80 Latitudes exceeding -90 or +90 degrees are truncated to -90 or +90
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81 respectively, in which case a warning will be issued. Longitudes exceeding -180
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82 or +180 degrees will be converted to values between -180 and +180 (both
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83 inclusive) by adding or substracting a multiple of 360 degrees, in which case a
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84 notice will be issued.
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85
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86 If the latitude is -90 or +90 (south pole or north pole), a longitude value is
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87 still stored in the datum, and if a point is on the prime meridian or the
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88 180th meridian, the east/west bit is also stored in the datum. In case of the
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89 prime meridian, this is done by storing a floating point value of -0 for
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90 0 degrees west and a value of +0 for 0 degrees east. In case of the
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91 180th meridian, this is done by storing -180 or +180 respectively. The equality
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92 operator, however, returns true when the same points on earth are described,
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93 i.e. the longitude is ignored for the poles, and 180 degrees west is considered
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94 to be equal to 180 degrees east.
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95
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96 #### `ebox`
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97
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98 An area on earth demarcated by a southern and northern latitude, and a western
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99 and eastern longitude (all given in WGS-84).
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100
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101 The text input format is
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102 `'{N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float>'`, where each float is in
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103 degrees. The ordering of the four white-space separated blocks is not
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104 significant. To include the 180th meridian, one longitude boundary must be
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105 equal to or exceed `W180` or `E180`, e.g. `'N10 N20 E170 E190'`.
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106
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107 A special value is the empty area, denoted by the text represenation `'empty'`.
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108 Such an `ebox` does not contain any point.
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109
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110 An `ebox` may also be created from four floating point numbers by calling
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111 `ebox(min_latitude, max_latitude, min_longitude, max_longitude)`, where
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112 positive values are used for north and east, and negative values are used for
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113 south and west. If `min_latitude` is strictly greater than `max_latitude`, an
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114 empty `ebox` is created. If `min_longitude` is greater than `max_longitude` and
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115 if both longitudes are between -180 and +180 degrees, then the area oriented in
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116 such way that the 180th meridian is included.
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117
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118 If the longitude span is less than 120 degrees, an `ebox` may be alternatively
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119 created from two `epoints` in the following way: `ebox(epoint(lat1, lon1),
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120 epoint(lat2, lon2))`. In this case `lat1` and `lat2` as well as `lon1` and
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121 `lon2` can be swapped without any impact.
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122
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123 #### `ecircle`
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124
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125 An area containing all points not farther away from a given center point
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126 (WGS-84) than a given radius.
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127
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128 The text input format is `'{N|S}<float> {E|W}<float> <float>'`, where the first
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129 two floats denote the center point in degrees and the third float denotes the
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130 radius in meters. A radius equal to minus infinity denotes an empty circle
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131 which contains no point at all (despite having a center), while a radius equal
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132 to zero denotes a circle that includes a single point.
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133
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134 An `ecircle` may also be created by calling `ecircle(epoint(...), radius)` or
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135 from three floating point numbers by calling `ecircle(latitude, longitude,
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136 radius)`.
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137
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138 #### `ecluster`
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139
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140 A collection of points, paths, polygons, and outlines on the WGS-84 spheroid.
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141 Each path, polygon, or outline must cover a longitude range of less than
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142 180 degrees to avoid ambiguities.
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143
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144 The text input format is a white-space separated list of the following items:
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145
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146 * `point ({N|S}<float> {E|W}<float>)`
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147 * `path ({N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> ...)`
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148 * `outline ({N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> ...)`
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149 * `polygon ({N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float> ...)`
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150
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151 Paths are open by default (i.e. there is no connection from the last point in
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152 the list to the first point in the list). Outlines and polygons, in contrast,
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153 are automatically closed (i.e. there is a line segment from the last point in
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154 the list to the first point in the list) which means the first point should not
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155 be repeated as last point in the list. Polygons are filled, outlines are not.
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156
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157 ### 2. Indices
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158
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159 Two kinds of indices are supported: B-tree and GiST indices.
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160
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161 #### B-tree indices
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162
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163 A B-tree index can be used for simple equality searches and is supported by the
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164 `epoint`, `ebox`, and `ecircle` data types. B-tree indices can not be used for
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165 geographic searches.
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166
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167 #### GiST indices
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168
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169 For geographic searches, GiST indices must be used. The `epoint`, `ecircle`,
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170 and `ecluster` data types support GiST indexing. A GiST index for geographic
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171 searches can be created as follows:
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172
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173 CREATE TABLE tbl (
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174 id serial4 PRIMARY KEY,
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175 loc epoint NOT NULL );
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176
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177 CREATE INDEX name_of_index ON tbl USING gist (loc);
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178
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179 GiST indices also support nearest neighbor searches when using the distance
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180 operator (`<->`) in the ORDER BY clause.
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181
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182 #### Indices on other data types (e.g. GeoJSON)
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183
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184 Note that further types can be indexed by using an index on an expression with
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185 a conversion function. One conversion function provided by pgLatLon is the
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186 `GeoJSON_to_ecluster(float8, float8, text)` function:
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187
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188 CREATE TABLE tbl (
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189 id serial4 PRIMARY KEY,
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190 loc jsonb NOT NULL );
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191
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192 CREATE INDEX name_of_index ON tbl USING gist((GeoJSON_to_ecluster("loc")));
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193
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194 When using the conversion function in an expression, the index will be used
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195 automatically:
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196
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197 SELECT * FROM tbl WHERE GeoJSON_to_ecluster("loc") && 'N50 E10 10000'::ecircle;
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198
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199 ### 3. Operators
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200
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201 #### Equality operator `=`
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202
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203 Tests if two geographic objects are equal.
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204
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205 The longitude is ignored for the poles, and 180 degrees west is considered to
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206 be equal to 180 degrees east.
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207
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208 For boxes and circles, two empty objects are considered equal. (Note that a
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209 circle is not empty if the radius is zero but only if it is negative infinity,
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210 i.e. smaller than zero.) Two circles with a positive infinite radius are also
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211 considered equal.
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212
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213 Implemented for:
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214
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215 * `epoint = epoint`
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216 * `ebox = ebox`
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217 * `ecircle = ecircle`
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218
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219 The negation is the inequality operator (`<>` or `!=`).
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220
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221 #### Linear ordering operators `<<<`, `<<<=`, `>>>=`, `>>>`
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222
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223 These operators create an arbitrary (but well-defined) linear ordering of
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224 geographic objects, which is used internally for B-tree indexing and merge
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225 joins. These operators will usually not be used by an application programmer.
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226
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227 #### Overlap operator `&&`
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228
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229 Tests if two geographic objects have at least one point in common. Currently
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230 implemented for:
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231
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232 * `epoint && ebox`
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233 * `epoint && ecircle`
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234 * `epoint && ecluster`
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235 * `ebox && ebox`
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236 * `ecircle && ecircle`
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237 * `ecircle && ecluster`
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238
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239 The `&&` operator is commutative, i.e. `a && b` is the same as `b && a`. Each
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240 commutation is supported as well.
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241
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242 #### Distance operator `<->`
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243
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244 Calculates the shortest distance between two geographic objects in meters (zero
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245 if the objects are overlapping). Currently implemented for:
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246
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247 * `epoint <-> epoint`
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248 * `epoint <-> ecircle`
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249 * `epoint <-> ecluster`
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250 * `ecircle <-> ecircle`
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251 * `ecircle <-> ecluster`
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252
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253 The `<->` operator is commutative, i.e. `a <-> b` is the same as `b <-> a`.
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254 Each commutation is supported as well.
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255
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256 For short distances, the result is very accurate (i.e. respects the dimensions
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257 of the WGS-84 spheroid). For longer distances in the order of magnitude of
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258 earth's radius or greater, the value is only approximate (but the error is
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259 still less than 0.2% as long as no polygons with very long edges are involved).
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260
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261 The functions `distance(epoint, epoint)` and `distance(ecluster, epoint)` can
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262 be used as an alias for this operator.
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263
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264 Note: In case of radial searches with a fixed radius, this operator should
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265 not be used. Instead, an `ecircle` should be created and used in combination
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266 with the overlap operator (`&&`). Alternatively, the functions
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267 `distance_within(epoint, epoint, float8)` or `distance_within(ecluster, epoint,
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268 float8)` can be used for fixed-radius searches.
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269
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270 ### 4. Functions
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271
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272 #### `center(circle)`
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273
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274 Returns the center of an `ecircle` as an `epoint`.
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275
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276 #### `distance(epoint, epoint)`
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277
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278 Calculates the distance between two `epoint` datums in meters. This function is
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279 an alias for the distance operator `<->`.
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280
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281 Note: In case of radial searches with a fixed radius, this function should not be
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282 used. Use `distance_within(epoint, epoint, float8)` instead.
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283
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284 #### `distance(ecluster, epoint)`
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285
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286 Calculates the distance from an `ecluster` to an `epoint` in meters. This
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287 function is an alias for the distance operator `<->`.
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288
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289 Note: In case of radial searches with a fixed radius, this function should not be
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290 used. Use `distance_within(epoint, epoint, float8)` instead.
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291
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292 #### `distance_within(`variable `epoint,` fixed `epoint,` radius `float8)`
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293
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294 Checks if the distance between two `epoint` datums is not greater than a given
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295 value (search radius).
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296
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297 Note: In case of radial searches with a fixed radius, the first argument must
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298 be used for the table column, while the second argument must be used for the
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299 search center. Otherwise an existing index cannot be used.
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300
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301 #### `distance_within(`variable `ecluster,` fixed `epoint,` radius `float8)`
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302
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303 Checks if the distance from an `ecluster` to an `epoint` is not greater than a
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304 given value (search radius).
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305
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306 #### `ebox(`latmin `float8,` latmax `float8,` lonmin `float8,` lonmax `float8)`
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307
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308 Creates a new `ebox` with the given boundaries.
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309 See "1. Types", subsection `ebox` for details.
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310
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311 #### `ebox(epoint, epoint)`
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312
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313 Creates a new `ebox`. This function may only be used if the longitude
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314 difference is less than or equal to 120 degrees.
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315 See "1. Types", subsection `ebox` for details.
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316
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317 #### `ecircle(epoint, float8)`
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318
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319 Creates an `ecircle` with the given center point and radius.
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320
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321 #### `ecircle(`latitude `float8,` longitude `float8,` radius `float8)`
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322
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323 Creates an `ecircle` with the given center point and radius.
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324
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325 #### `ecluster_concat(ecluster, ecluster)`
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326
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327 Combines two clusters to form a new `ecluster` by uniting all entries of both
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328 clusters. Note that two overlapping areas of polygons annihilate each other
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329 (which may be used to create polygons with holes).
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330
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331 #### `ecluster_concat(ecluster[])`
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332
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333 Creates a new `ecluster` that unites all entries of all clusters in the passed
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334 array. Note that two overlapping areas of polygons annihilate each other (which
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335 may be used to create polygons with holes).
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336
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337 #### `ecluster_create_multipoint(epoint[])`
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338
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339 Creates a new `ecluster` which contains multiple points.
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340
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341 #### `ecluster_create_outline(epoint[])`
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342
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343 Creates a new `ecluster` that is an outline given by the passed points.
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344
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345 #### `ecluster_create_path(epoint[])`
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346
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347 Creates a new `ecluster` that is a path given by the passed points.
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348
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349 #### `ecluster_create_polygon(epoint[])`
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350
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351 Creates a new `ecluster` that is a polygon given by the passed points.
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352
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353 #### `ecluster_extract_outlines(ecluster)`
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354
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355 Set-returning function that returns the outlines of an `ecluster` as `epoint[]`
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356 rows.
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357
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358 #### `ecluster_extract_paths(ecluster)`
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359
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360 Set-returning function that returns the paths of an `ecluster` as `epoint[]`
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361 rows.
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362
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363 #### `ecluster_extract_points(ecluster)`
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364
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365 Set-returning function that returns the points of an `ecluster` as `epoint`
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366 rows.
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367
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368 #### `ecluster_extract_polygons(ecluster)`
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369
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370 Set-returning function that returns the polygons of an `ecluster` as `epoint[]`
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371 rows.
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372
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373 #### `empty_ebox`()
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374
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375 Returns the empty `ebox`.
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376 See "1. Types", subsection `ebox` for details.
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377
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378 #### `epoint(`latitude `float8,` longitude `float8)`
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379
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380 Returns an `epoint` with the given latitude and longitude.
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381
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382 #### `epoint_latlon(`latitude `float8,` longitude `float8)`
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383
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384 Alias for `epoint(float8, float8)`.
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385
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386 #### `epoint_lonlat(`longitude `float8,` latitude `float8)`
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387
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388 Same as `epoint(float8, float8)` but with arguments reversed.
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389
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390 #### `GeoJSON_to_epoint(jsonb, text)`
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391
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392 Maps a GeoJSON object of type "Point" or "Feature" (which contains a
|
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393 "Point") to an `epoint` datum. For any other JSON objects, NULL is returned.
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394
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395 The second parameter (which defaults to `epoint_lonlat`) may be set to a name
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396 of a conversion function that transforms two coordinates (two `float8`
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397 parameters) to an `epoint`.
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398
|
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399 #### `GeoJSON_to_ecluster(jsonb, text)`
|
|
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400
|
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401 Maps a (valid) GeoJSON object to an `ecluster`. Note that this function
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402 does not check whether the JSONB object is a valid GeoJSON object.
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403
|
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404 The second parameter (which defaults to `epoint_lonlat`) may be set to a name
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405 of a conversion function that transforms two coordinates (two `float8`
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406 parameters) to an `epoint`.
|
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407
|
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408 #### `max_latitude(ebox)`
|
|
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|
409
|
|
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410 Returns the northern boundary of a given `ebox` in degrees between -90 and +90.
|
|
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411
|
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|
412 #### `max_longitude(ebox)`
|
|
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|
413
|
|
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414 Returns the eastern boundary of a given `ebox` in degrees between -180 and +180
|
|
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415 (both inclusive).
|
|
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|
416
|
|
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|
417 #### `min_latitude(ebox)`
|
|
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|
418
|
|
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|
419 Returns the southern boundary of a given `ebox` in degrees between -90 and +90.
|
|
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|
420
|
|
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|
421 #### `min_longitude(ebox)`
|
|
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|
422
|
|
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|
423 Returns the western boundary of a given `ebox` in degrees between -180 and +180
|
|
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|
424 (both inclusive).
|
|
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|
425
|
|
jbe@0
|
426 #### `latitude(epoint)`
|
|
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|
427
|
|
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|
428 Returns the latitude value of an `epoint` in degrees between -90 and +90.
|
|
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|
429
|
|
jbe@0
|
430 #### `longitude(epoint)`
|
|
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|
431
|
|
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|
432 Returns the longitude value of an `epoint` in degrees between -180 and +180
|
|
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|
433 (both inclusive).
|
|
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|
434
|
|
jbe@0
|
435 #### `radius(ecircle)`
|
|
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|
436
|
|
jbe@0
|
437 Returns the radius of an `ecircle` in meters.
|
|
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|
438
|