[GIS] PostGIS spatial reference ID (SRID) for regular cartesian coordinate system

coordinate systemepsgpostgispostgresqlsrid

I would like to store a polygon as a set of 2D points represented as x, y coordinates of a Cartesian coordinate system.

Which spatial reference can I use? Looking at my spatial_ref_sys table, all the spatial references seem to be geography related.

The points of the polygon would represent satellite measurements which I would invoke ST_ConvexHull on to get the shape of the satellite footprint.

Best Answer

If you do no reprojection with the data, it does not really matter what projected CRS you are using.

You can use EPSG:3857 (Google Mercator), if your data does not exceed the bounds of

-20037508.34,-20037508.34,20037508.34,20037508.34

(Not sure what happens if the data is outside those bounds)

Related Solutions

Coordinate System – Determining if Spatial Reference is Geographic or Projected Using ArcObjects

You can check the object type like so:

ISpatialReference ref = ...; // This is your spatial reference
if (ref is IGeographicCoordinateSystem) {
    //Geographic
} else if (ref is IProjectedCoordinateSystem) {
    // Projected
} else {
    // Unknown coordinate system
}

[GIS] Setting spatial reference to OSGB_1936_British_National_Grid in ArcGIS Desktop

In ArcGIS 10, if you go into, for example the Data Frame Properties, and go to the "Predefined" co-ordinate systems, you can click on two co-ordinate systems you mentioned in the question - OSGB 1936, and British National Grid, if you click "Modify" on both you will see that they actually both use the OSGB 1936 Datum (click on "Modify" again on BNG to see the Datum).

You probably want to use the British National Grid Co-ordinate system, because it is the basis of all Ordnance Survey Grid references- basically the projection is a set of mathmatical formulae that maps real world positions onto the co-ordinate system that is used in the UK. Not entirely sure what the OSGB_1936 co-ordinate system would be, but the major difference between a geographic and projected co-ordinate system is that:

"Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across the two dimensions" (ArcGIS 10 Help File).

This obviously makes it much more useful for precision applications such as plans, although this accuracy will generally only be high over a relatively small area compared to a geographic co-ordinate system, which is suitable for describing a point with (relative) accuracy over the whole earth's surface.

Best Answer

Related Solutions

Coordinate System – Determining if Spatial Reference is Geographic or Projected Using ArcObjects

[GIS] Setting spatial reference to OSGB_1936_British_National_Grid in ArcGIS Desktop

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