Projection Basics¶
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This tutorial introduces the basic classes, methods, and functions of the proj module. It focuses mainly on basic topics such as:
Projection construction and representation
Coordinate reference system transformations
EPSG¶
The European Petroleum Survey Group is the body that maintains the EPSG Geodetic Parameter Dataset, better known as the “EPSG database”. This dataset is the primary source of supported coordinate reference systems in GeoTools, and by extension GeoScript.
Projection Objects¶
The Projection class is the primary class of the proj module. Projection objects can be constructed in one of two ways. The first is by specifying an EPSG code reference. The second is by specifying the Well Known Text (WKT) of the coordinate reference system directly.
>>> from geoscript.proj import Projection
>>> Projection('EPSG:4326')
GEOGCS["WGS 84",
DATUM["World Geodetic System 1984",
SPHEROID["WGS 84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]],
UNIT["degree", 0.017453292519943295],
AXIS["Geodetic latitude", NORTH],
AXIS["Geodetic longitude", EAST],
AUTHORITY["EPSG","4326"]]
>>> Projection('GEOGCS["GCS_WGS_1984",DATUM["WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]]')
GEOGCS["GCS_WGS_1984",
DATUM["WGS_1984",
SPHEROID["WGS_1984", 6378137.0, 298.257223563]],
PRIMEM["Greenwich", 0.0],
UNIT["degree", 0.017453292519943295],
AXIS["Longitude", EAST],
AXIS["Latitude", NORTH]]
js> var proj = require("geoscript/proj")
js> var wgs84 = proj.Projection("epsg:4326")
js> wgs84
<Projection EPSG:4326>
js> wgs84.wkt
GEOGCS["WGS 84",
DATUM["World Geodetic System 1984",
SPHEROID["WGS 84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]],
UNIT["degree", 0.017453292519943295],
AXIS["Geodetic longitude", EAST],
AXIS["Geodetic latitude", NORTH],
AUTHORITY["EPSG","4326"]]
js> var p = proj.Projection('GEOGCS["GCS_WGS_1984",DATUM["WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]]')
js> p
<Projection EPSG:4326>
groovy:000> import geoscript.proj.Projection
groovy:000> p = new Projection("EPSG:4326")
===> EPSG:4326
groovy:000> p.id
===> EPSG:4326
groovy:000> p.wkt
===> GEOGCS["WGS 84",
DATUM["World Geodetic System 1984",
SPHEROID["WGS 84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]],
UNIT["degree", 0.017453292519943295],
AXIS["Geodetic longitude", EAST],
AXIS["Geodetic latitude", NORTH],
AUTHORITY["EPSG","4326"]]
groovy:000> p = new Projection('GEOGCS["GCS_WGS_1984",DATUM["WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]]')
groovy:000> p.wkt
===> GEOGCS["GCS_WGS_1984",
DATUM["WGS_1984",
SPHEROID["WGS_1984", 6378137.0, 298.257223563]],
PRIMEM["Greenwich", 0.0],
UNIT["degree", 0.017453292519943295],
AXIS["Longitude", EAST],
AXIS["Latitude", NORTH]]
groovy:000> p.id
===> EPSG:432
See also
See also
See also
Determining EPSG Codes¶
Often a spatial reference system is encountered that does not have an EPSG code associated with it. This can happen for a few different reasons.
The coordinate reference system does not exist in the EPSG database
The WKT representation is not complete enough to map to an EPSG entry
>>> from geoscript.proj import Projection
>>> wkt = 'PROJCS["NAD_1983_HARN_StatePlane_Colorado_Central_FIPS_0502_Feet", GEOGCS["GCS_North_American_1983_HARN", DATUM["Unknown", SPHEROID["GRS_1980", 6378137.0, 298.257222101]], PRIMEM["Greenwich", 0.0], UNIT["degree", 0.017453292519943295], AXIS["Longitude", EAST], AXIS["Latitude", NORTH]], PROJECTION["Lambert_Conformal_Conic_2SP"], PARAMETER["central_meridian", -105.5], PARAMETER["latitude_of_origin", 37.833333333333336], PARAMETER["standard_parallel_1", 39.75], PARAMETER["false_easting", 3000000.000316083], PARAMETER["false_northing", 999999.999996], PARAMETER["scale_factor", 1.0], PARAMETER["standard_parallel_2", 38.45], UNIT["foot_survey_us", 0.3048006096012192], AXIS["X", EAST], AXIS["Y", NORTH]]'
>>> p = Projection(wkt)
>>> p.id
None
js> var proj = require("geoscript/proj")
js> var wkt = 'PROJCS["NAD_1983_HARN_StatePlane_Colorado_Central_FIPS_0502_Feet", GEOGCS["GCS_North_American_1983_HARN", DATUM["Unknown", SPHEROID["GRS_1980", 6378137.0, 298.257222101]], PRIMEM["Greenwich", 0.0], UNIT["degree", 0.017453292519943295], AXIS["Longitude", EAST], AXIS["Latitude", NORTH]], PROJECTION["Lambert_Conformal_Conic_2SP"], PARAMETER["central_meridian", -105.5], PARAMETER["latitude_of_origin", 37.833333333333336], PARAMETER["standard_parallel_1", 39.75], PARAMETER["false_easting", 3000000.000316083], PARAMETER["false_northing", 999999.999996], PARAMETER["scale_factor", 1.0], PARAMETER["standard_parallel_2", 38.45], UNIT["foot_survey_us", 0.3048006096012192], AXIS["X", EAST], AXIS["Y", NORTH]]'
js> var p = proj.Projection(wkt)
js> p
<Projection>
js> p.id === undefined
true
groovy:000> import geoscript.proj.Projection
groovy:000> wkt = 'PROJCS["NAD_1983_HARN_StatePlane_Colorado_Central_FIPS_0502_Feet", GEOGCS["GCS_North_American_1983_HARN", DATUM["Unknown", SPHEROID["GRS_1980", 6378137.0, 298.257222101]], PRIMEM["Greenwich", 0.0], UNIT["degree", 0.017453292519943295], AXIS["Longitude", EAST], AXIS["Latitude", NORTH]], PROJECTION["Lambert_Conformal_Conic_2SP"], PARAMETER["central_meridian", -105.5], PARAMETER["latitude_of_origin", 37.833333333333336], PARAMETER["standard_parallel_1", 39.75], PARAMETER["false_easting", 3000000.000316083], PARAMETER["false_northing", 999999.999996], PARAMETER["scale_factor", 1.0], PARAMETER["standard_parallel_2", 38.45], UNIT["foot_survey_us", 0.3048006096012192], AXIS["X", EAST], AXIS["Y", NORTH]]'
groovy:000> p = new Projection(wkt)
===> PROJCS["NAD_1983_HARN_StatePlane_Colorado_Central_FIPS_0502_Feet",
GEOGCS["GCS_North_American_1983_HARN",
DATUM["Unknown",
SPHEROID["GRS_1980", 6378137.0, 298.257222101]],
PRIMEM["Greenwich", 0.0],
UNIT["degree", 0.017453292519943295],
AXIS["Longitude", EAST],
AXIS["Latitude", NORTH]],
PROJECTION["Lambert_Conformal_Conic_2SP"],
PARAMETER["central_meridian", -105.5],
PARAMETER["latitude_of_origin", 37.833333333333336],
PARAMETER["standard_parallel_1", 39.75],
PARAMETER["false_easting", 3000000.000316083],
PARAMETER["false_northing", 999999.999996],
PARAMETER["scale_factor", 1.0],
PARAMETER["standard_parallel_2", 38.45],
UNIT["foot_survey_us", 0.3048006096012192],
AXIS["X", EAST],
AXIS["Y", NORTH]]
groovy:000> p.id
===> null
In this case some useful online resources are:
Catalogue of many spatial reference systems.
Service for mapping projection Well Known Text to the EPSG database.
