[OSRS-PROJ] Fw: [GRASSLIST:1481] Re: Bug in s.proj?

[Hamish]

[fwd from the GRASS list, maybe someone here has an idea?  -Hamish]



Date: Mon, 13 Oct 2003 16:02:36 +0100
From: "David Orme" <d.orme at imperial.ac.uk>
To: GRASSLIST at baylor.edu
Subject: [GRASSLIST:1481] Re: Bug in s.proj?


Hi,

OK - I've followed Hamish's suggestion and used cs2cs from PROJ.4 (I'll 
get to Grass 5.3 soon) to check the location of a test point (0 m E, 
7332956.368 m N) from a Behrmann projection back into geographic 
coordinates:

[doibook:/usr/local/bin] dorme% ./cs2cs +proj=cea +lat_ts=30 
+datum=WGS84 +to +proj=latlong +datum=WGS84
0 7332956.368
0dE     86d18'12.382"N 0.000

This gives me the same geographic coordinate as I got from my original 
use of s.proj in Grass 5.0.2. To test ArcMAP again, I created a 
shapefile with a Behrmann projection containing a single point at the 
test location and used the project wizard in ArcToolbox to change to a 
Geographic projection (wgs84.prj). The resulting point has the 
following geographic coordinates:

0dE 87d 7' 58.42" N

The output of g.projinfo for my Behrmann location is below. I'm using 
Mac OS X (version 10.2.8) and the following version of cs2cs:

[doibook:/usr/local/bin] dorme% ./cs2cs
Rel. 4.4.7, 31 March 2003
usage: cs2cs [ -eEfIlrstvwW [args] ] [ +opts[=arg] ]
                    [+to [+opts[=arg] [ files ]

David.

-----------------------------------------------------------
PROJ_INFO file:
name:    Equal Area Cylindrical
datum:   wgs84
dx:      0.000000
dy:      0.000000
dz:      0.000000
proj:    cea
ellps:   wgs84
a:       6378137.0000000000
es:      0.0066943800
f:       298.2572235630
lat_0:   0.0000000000
lat_ts:  30.0000000000
lon_0:   0.0000000000
-----------------------------------------------------------
PROJ_UNITS file:
unit:    meter
units:   meters
meters:  1.000000
-----------------------------------------------------------


>> I e-mailed yesterday about a mismatch between Arcmap and Grass 5.0.2
>> transformations of sites from a global cylindrical equal area location
>> to a geographic. I've been playing around some more and it looks to me
>> as if either:
>>
>> 1) s.proj has a bug in it,
>> 2) arcmap has a bug in the transformation of sites or,
>> 3) I've missed something elementary.
>>
>> I created a point shapefile in arcmap of the centre points of the grid
>> cells for the CEA location and read this into grass using s.in.shape.
>> I've checked that the values in the sites file are what I was
>> expecting. I used s.proj to project these sites into a geographic
>> (wgs84) location. I also used arcmap to project the original behrmann
>> points shapefile into wgs84 and then imported this into my grass wgs84
>> location using s.in.shape. The two sets of sites are not in the same
>> place - in extreme latitudes the discrepancy is about half a degree. I
>> won't attach the files to preserve bandwidth but if anyone wants them,
>> let me know.
>>
>> Any suggestions?



-----------------------------------------------------------------------

From: "John Gillette" <JGillette at rfmd.com>
Subject: [GRASSLIST:1484] Re: Bug in s.proj?
Date: Mon, 13 Oct 2003 17:56:31 -0400
To: "David Orme" <d.orme at imperial.ac.uk>, <GRASSLIST at baylor.edu>
Sender: owner-GRASSLIST at baylor.edu

For a second opinion, I down loaded GEOTRANS 2.2.3 for
Windows.

WGS84, CEA, 0,7332956.368 to WGS84, Geodetic gives
0d 0' 0.0004"E 87d 7' 58.1173"N

This is .544 Meters from ArcMAP answer.

m.proj in Grass 5.0.0 gives same answer as cs2cs.

John

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