[Proj] Cassini coordinate reprojection problem

christopher.faulkner at ntlworld.com christopher.faulkner at ntlworld.com
Wed Mar 16 04:05:29 EST 2005



> that you should either use the +ellps option OR the 
> +a=/+es= ---one does
> not know which proj will use without digging into the 
> code.  The 
> +a=/+es=
> values do seem to match the +ellps=airy values however.

Changing these values does not seem to alter the output much. Even if I remove them, I get pretty much the same result.

> Please determine what the inverse of the Cassini value 
> your alternate
> software gives and how that compares with the proj 
> inverse.  If that 
> value
> does not agree then there is no point in going further.
> Try the SAME geographic coordinates for the forward
> projection for Transverse Mercator on all systems and 
> check for
> differences.

Will do - I'll let you know.

> Are you sure that the other systems are NOT doing a datum 
> transformation?

GEOTRANS might be but certainly genamap isn't. The supplier created the coordinates without datum shifting. Would the datum shift make a difference of 100m or more ?
> Also, your "proj +proj=list" is not a valid command.  If you want a 
> list of
> projections then "proj -lp" (or lP) and for a list of ellipsoids "proj 
> -le"


Thanks for that and the other scripts. proj +proj=list was what I got from the manual. 

> PLEASE keep us informed or your progress.

I certainly will ! The strange thing about all this is that I used proj4 back in about 2001 and found that it reprojected Cassini just the same as genamap.


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