[postgis-users] Custom CRS for a local survey grid

[Mike Toews]

Hi all,

I am working with spatial data that has been collected for the past 
several decades at a site using a custom local coordinate system. I have 
a few points at this site where I know both the local grid and the world 
coordinates. Ideally, I'd like to define a custom srid to transform 
between projections.

I would like to know more about adding new coordinate reference systems 
to the spatial_ref_sys table, however I need to know a few things:

   1. Do I need to define all of: srid, auth_name, auth_srid, srtext,
      and proj4text fields in the spatial_ref_sys table? Or only a few
      fields (specify which are required or optional)?
   2. How would I define the projection for a local survey grid? (I may
      alternately ask this on the proj mail list)

At present, I have a spreadsheet to scale, translate and rotate points 
to NAD83/UTM9N, or I use similar commands in CAD for drawings, but I 
have much more work, and I'd like to make the translation more streamlined.

Any suggestions, answers, hints, or examples would be greatly appreciated.

Best regards,
-Mike