[OSRS-PROJ] PROJ.4 "proj=latlong ellps=GRS80" functionality?

Ed McNierney ed at topozone.com
Fri Aug 3 12:08:24 EDT 2001

I'm having a hard time understanding how this functionality is supposed
to work.  I've built PROJ 4.4.3 with no troubles (Windows 2000,
Microsoft VC++) and everything seems to be working.

I don't understand the results I'm getting from "proj=latlong
ellps=GRS80", however.  I'm ultimately trying to use this in MapServer,
where I have several input data layers in NAD83 decimal degrees that I'm
trying to project to UTM.

Here's the simple example I don't understand:

C:\>proj -v +proj=latlong +ellps=GRS80
#Lat/long (Geodetic)
# +proj=latlong +ellps=GRS80
-71 43
-1.24   0.75

That is, my input coordinate (-71, 43) is transformed to (-1.24, 0.75).
What does this mean?  I would expect the output results to be either
identical to my input (if the input data is presumed to be in the output
ellipsoid or if GRS80 or WGS84 is the default) or I would expect them to
be very slightly different (if the input ellipsoid is something else).

It would be extremely helpful if someone could explain this output to me
- thanks!

	- Ed

Ed McNierney
Chief Mapmaker
ed at topozone.com
(978) 251-4242

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