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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.

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You could just keep the srid as -1. –  Devdatta Tengshe Jun 24 '13 at 9:06
    
Are you sure I could store points with an invalid SRID? I don't think that the ST_ConvexHull function would work. –  Zoltán Jun 24 '13 at 9:15
    
I have just tested with a layer having srid=-1, and ST_ConvexHull can be used without any issues. –  Devdatta Tengshe Jun 24 '13 at 9:51
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1 Answer 1

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)

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Yes, I ended up deciding to use something like this, only I chose EPSG:3395 (World Mercator). Any reason why I should prefer Google Mercator? My positions are in the range -250000 to 250000, so I should be safe. –  Zoltán Jun 24 '13 at 11:46
    
EPSG:3395 should do as well. –  Andre Joost Jun 24 '13 at 11:53
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