Configure Spatial Reference Systems (SRS)¶

A spatial reference system (SRS) or coordinate reference system (CRS) is a framework used to precisely measure locations on, or relative to, the Earth's surface. GeoKit offers a variety of options for specifying these systems, which are introduced here. If you are new to spatial reference system you could start here: https://en.wikipedia.org/wiki/Spatial_reference_system

Load required libraries¶

In [1]:

import geokit.core.srs

import geokit.core.srs

Common Spatial Reference System (SRS)¶

Commonly used SRS:

• Basic latitude and longitude - EPSG4326
• Lambert azimuthal equal area (LAEA) - EPSG3035
• Mercator - EPSG3857

In [2]:

print(type(geokit.core.srs.EPSG4326))

print(type(geokit.core.srs.EPSG4326))

<class 'osgeo.osr.SpatialReference'>

In [3]:

print(geokit.core.srs.EPSG4326)
print(geokit.core.srs.EPSG3035)
print(geokit.core.srs.EPSG3857)

print(geokit.core.srs.EPSG4326) print(geokit.core.srs.EPSG3035) print(geokit.core.srs.EPSG3857)

GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,
        AUTHORITY["EPSG","9122"]],
    AXIS["Latitude",NORTH],
    AXIS["Longitude",EAST],
    AUTHORITY["EPSG","4326"]]
PROJCS["ETRS89-extended / LAEA Europe",
    GEOGCS["ETRS89",
        DATUM["European_Terrestrial_Reference_System_1989",
            SPHEROID["GRS 1980",6378137,298.257222101,
                AUTHORITY["EPSG","7019"]],
            AUTHORITY["EPSG","6258"]],
        PRIMEM["Greenwich",0,
            AUTHORITY["EPSG","8901"]],
        UNIT["degree",0.0174532925199433,
            AUTHORITY["EPSG","9122"]],
        AUTHORITY["EPSG","4258"]],
    PROJECTION["Lambert_Azimuthal_Equal_Area"],
    PARAMETER["latitude_of_center",52],
    PARAMETER["longitude_of_center",10],
    PARAMETER["false_easting",4321000],
    PARAMETER["false_northing",3210000],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Northing",NORTH],
    AXIS["Easting",EAST],
    AUTHORITY["EPSG","3035"]]
PROJCS["WGS 84 / Pseudo-Mercator",
    GEOGCS["WGS 84",
        DATUM["WGS_1984",
            SPHEROID["WGS 84",6378137,298.257223563,
                AUTHORITY["EPSG","7030"]],
            AUTHORITY["EPSG","6326"]],
        PRIMEM["Greenwich",0,
            AUTHORITY["EPSG","8901"]],
        UNIT["degree",0.0174532925199433,
            AUTHORITY["EPSG","9122"]],
        AUTHORITY["EPSG","4326"]],
    PROJECTION["Mercator_1SP"],
    PARAMETER["central_meridian",0],
    PARAMETER["scale_factor",1],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH],
    EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs"],
    AUTHORITY["EPSG","3857"]]

LoadSRS from Various Specifications¶

The LoadSRS function can be used to load spatial reference systems using various formats.

EPSG Integers¶

Integers are treated as SRS from epsg.io:

In [4]:

print(geokit.core.srs.loadSRS(2004))

print(geokit.core.srs.loadSRS(2004))

PROJCS["Montserrat 1958 / British West Indies Grid",
    GEOGCS["Montserrat 1958",
        DATUM["Montserrat_1958",
            SPHEROID["Clarke 1880 (RGS)",6378249.145,293.465,
                AUTHORITY["EPSG","7012"]],
            AUTHORITY["EPSG","6604"]],
        PRIMEM["Greenwich",0,
            AUTHORITY["EPSG","8901"]],
        UNIT["degree",0.0174532925199433,
            AUTHORITY["EPSG","9122"]],
        AUTHORITY["EPSG","4604"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",-62],
    PARAMETER["scale_factor",0.9995],
    PARAMETER["false_easting",400000],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH],
    AUTHORITY["EPSG","2004"]]

Proj4 string¶

Otherwise, SRS can be loaded from their Proj4 string:

In [5]:

poland_special_srs = geokit.core.srs.loadSRS(
    'PROJCS["PUWG_42_Strefa_4",GEOGCS["GCS_Pulkovo_1942",DATUM["Pulkovo_1942",SPHEROID["Krasovsky_1940",6378245,298.3]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",4500000],PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",21],PARAMETER["Scale_Factor",1],PARAMETER["Latitude_Of_Origin",0],UNIT["Meter",1]]'
)

print(poland_special_srs)

poland_special_srs = geokit.core.srs.loadSRS( 'PROJCS["PUWG_42_Strefa_4",GEOGCS["GCS_Pulkovo_1942",DATUM["Pulkovo_1942",SPHEROID["Krasovsky_1940",6378245,298.3]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",4500000],PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",21],PARAMETER["Scale_Factor",1],PARAMETER["Latitude_Of_Origin",0],UNIT["Meter",1]]' ) print(poland_special_srs)

PROJCS["PUWG_42_Strefa_4",
    GEOGCS["Pulkovo 1942",
        DATUM["Pulkovo_1942",
            SPHEROID["Krassowsky 1940",6378245,298.3,
                AUTHORITY["EPSG","7024"]]],
        PRIMEM["Greenwich",0],
        UNIT["Degree",0.0174532925199433]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",21],
    PARAMETER["scale_factor",1],
    PARAMETER["false_easting",4500000],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH]]

Center the SRS to Coordinate¶

SRS can be centered to a coordinate, for example centered to Aachen:

In [6]:

aachen_centered_srs = geokit.core.srs.centeredLAEA(6.083, 50.775)
print(aachen_centered_srs)

aachen_centered_srs = geokit.core.srs.centeredLAEA(6.083, 50.775) print(aachen_centered_srs)

PROJCS["unnamed_m",
    GEOGCS["GRS 1980(IUGG, 1980)",
        DATUM["unknown",
            SPHEROID["GRS80",6378137,298.257222101],
            TOWGS84[0,0,0,0,0,0,0]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433]],
    PROJECTION["Lambert_Azimuthal_Equal_Area"],
    PARAMETER["latitude_of_center",50.775],
    PARAMETER["longitude_of_center",6.083],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["Meter",1],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH]]

Transformation Between Coordinate Systems¶

In [7]:

# transforming points between SRS's
new_points = geokit.core.srs.xyTransform(
    [
        (6.083, 50.775),
        (6.083, 50.875),
        (6.083, 50.975),
        (7.083, 50.175),
        (7.583, 50.775),
    ],
    fromSRS=geokit.core.srs.EPSG4326,
    toSRS=aachen_centered_srs,
    outputFormat="xy",
)

# transforming points between SRS's new_points = geokit.core.srs.xyTransform( [ (6.083, 50.775), (6.083, 50.875), (6.083, 50.975), (7.083, 50.175), (7.583, 50.775), ], fromSRS=geokit.core.srs.EPSG4326, toSRS=aachen_centered_srs, outputFormat="xy", )

In [8]:

for x, y in zip(new_points.x, new_points.y):
    print(x, y)

for x, y in zip(new_points.x, new_points.y): print(x, y)

0.0 0.0
0.0 11124.480318935728
0.0 22249.12252108337
71432.80781956235 -66262.41755972906
105796.52244980003 1069.9939140465938

Export the SRS¶

The coordinate systems can be exported. File formats for that are: WKT or Proj4

In [9]:

# Export as WKT
aachen_centered_srs.ExportToWkt()

# Export as WKT aachen_centered_srs.ExportToWkt()

Out[9]:

'PROJCS["unnamed_m",GEOGCS["GRS 1980(IUGG, 1980)",DATUM["unknown",SPHEROID["GRS80",6378137,298.257222101],TOWGS84[0,0,0,0,0,0,0]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["latitude_of_center",50.775],PARAMETER["longitude_of_center",6.083],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1],AXIS["Easting",EAST],AXIS["Northing",NORTH]]'

In [10]:

# Export to Proj4
aachen_centered_srs.ExportToProj4()

# Export to Proj4 aachen_centered_srs.ExportToProj4()

Out[10]:

'+proj=laea +lat_0=50.775 +lon_0=6.083 +x_0=0 +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs'

Load SRS¶

In [11]:

geokit.core.srs.loadSRS(aachen_centered_srs.ExportToWkt())

geokit.core.srs.loadSRS(aachen_centered_srs.ExportToWkt())

Out[11]:

<osgeo.osr.SpatialReference; proxy of <Swig Object of type 'OSRSpatialReferenceShadow *' at 0x7e451c5872a0> >