$webwork.htmlEncode($page.space.name) : Custom projection definition in PostGIS

This page last changed on Oct 20, 2006 by aaime.

Custom projection definition in PostGis.

Sometimes we need to store geometries that are in a projection which is not defined in the spatial_sys_ref PostGis table.

For example, recently I needed to store geometries which were projected in a Lambert Conformal Conic projection with the following parameters:

Projection parameters (as reported in QGis)

PROJCS[ "unnamed ",GEOGCS[ "WGS 84 ",DATUM[ "WGS_1984 ",
SPHEROID[ "WGS 84 ",6378137,298.2572235629972,AUTHORITY[ "EPSG ", "7030 "]],AUTHORITY[ "EPSG ", "6326 "]],
PRIMEM[ "Greenwich ",0],UNIT[ "degree (supplier to define representation) ",0.01745329251994328],AUTHORITY[ "EPSG ", "4326 "]],
PROJECTION[ "Lambert_Conformal_Conic_2SP "],
PARAMETER[ "standard_parallel_1 ",33.00000000000004],
PARAMETER[ "standard_parallel_2 ",45.00000000000004],
PARAMETER[ "latitude_of_origin ",40.00333786010746],
PARAMETER[ "central_meridian ",-97.0000000000001],
PARAMETER[ "false_easting ",0],
PARAMETER[ "false_northing ",0],UNIT[ "metre ",1,AUTHORITY[ "EPSG ", "9001 "]]]

To store the parameters for this projection in the spatial_ref_sys table, I created the following INSERT statement:

INSERT INTO "spatial_ref_sys" (srid, auth_name, auth_srid, srtext, proj4text) VALUES (104307, 'WRF',104307, 
'PROJCS["WRF_Lambert_Conformal_Conic 2",GEOGCS["GCS_North_American_1983",
DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137,298.25722356300003]],
PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943299]],
PROJECTION["Lambert_Conformal_Conic"],PARAMETER["False_Easting",0],
PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",-97],PARAMETER["Standard_Parallel_1",33],
PARAMETER["Standard_Parallel_2",60],PARAMETER["Latitude_Of_Origin",40.0],UNIT["Meter",1]]','+proj=lcc +lat_1=33 +lat_2=45 +lat_0=40.0 +lon_0=-97.0 +x_0=0 +y_0=0 +ellps=WGS84 +units=m');

The srid code ( in thsi case, 104307) was just the next available in the srid sequence.
It was also mentioned that there are guidelines as to which codes to use for user-defined projections: EPSG.org
From now on, this projection can be used for your geometries:

create table contours (gid serial);
 select AddGeometryColumn('burn','contours','geom','104306','MULTILINESTRING',2);
 INSERT INTO contours(gid,geom) VALUES(9, GeometryFromText('MULTILINESTRING ((1633500.0 251214.30448187666,1645746.4486482088 256500.0,1633500.0 266307.86663788836))', 104307) );