[GRASS5] [bug #3630] (grass) error in v.proj/r.proj in gnomonic projection

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this bug's URL: http://intevation.de/rt/webrt?serial_num=3630
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Subject: error in v.proj/r.proj in gnomonic projection

Platform: GNU/Linux/i386
grass obtained from: Trento Italy site
grass binary for platform: Downloaded precompiled Binaries
GRASS Version: 6.0.1

If gnomonic projection is set up, using the v.proj and r.proj in order to reproject maps from various projection (lat-lon, S-42 etc)  results in erroneous north-south shift of about 20-30 km (cca 0.2 degree od latitude). When using 'd.where', typical points shows latitude souther than it should. The east-west coordinates are OK. 

I have spent a lot of time searching for an error of mine, but was not successful. In the grass version 5.0.3 it worked OK. Unfortunately, the system does not allow to install the old version again. Before i start working on a workaround, I'd like to make sure if it cannot be fixed here. I still cannot exclude my error. 

If data are importet to the 'gnomonic' location from external source, 'd.where' shows exact location in lat-lon, exactly as 'proj' itself computes.

I repeated the problem also on Spearfish dataset; I set up location spearfish_gnom, here is the projection info:

GRASS 6.0.1 (spearfish_gnom):~ > g.proj -p -d -j -w -e   
-PROJ_INFO-------------------------------------------------
name       : Gnomonic
proj       : gnom
a          : 6379000.0000000000
es         : 0.0
f          : 0.0
lat_0      : 44.4600000000
lon_0      : -103.8500000000
-PROJ_UNITS------------------------------------------------
unit       : meter
units      : meters
meters     : 1.0
Datum name not present
Datum parameters not present
+proj=gnom
+lat_0=44.4600000000
+lon_0=-103.8500000000
+a=6379000
+b=6379000
+no_defs
PROJCS["Gnomonic",
    GEOGCS["Unknown",
        DATUM["D_unknown",
            SPHEROID["Unknown",6379000,"inf"]],
        PRIMEM["Greenwich",0],
        UNIT["Degree",0.017453292519943295]],
    PROJECTION["Gnomonic"],
    PARAMETER["latitude_of_origin",44.46],
    PARAMETER["central_meridian",-103.85],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["Meter",1]]
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I set up a new location spearfish_gnom with following parameters 
(for faster calculation I chose coarser resolution than orig. Spearfish dataset):

$cat PROJ_INFO:
name: Gnomonic
proj: gnom
a: 6379000.0000000000
es: 0.0
f: 0.0
lat_0: 44.4600000000
lon_0: -103.8500000000

$cat DEFAULT_WIND:
proj:       99
zone:       0
north:      5000
south:      -30000
east:       20000
west:       -2000
cols:       220
rows:       350
e-w resol:  100
n-s resol:  100
top:        1
bottom:     0
cols3:      1
rows3:      1
depths:     1
e-w resol3: 1
n-s resol3: 1
t-b resol:  1

I reprojected elevation.dem from spearfish to spearfish_gnom and found that 
there was an evident shift in NS (y) direction of about 0.20 degree. East-west 
direction was OK. 

I repeated the error shift on 3 PC, two of them running Mandrake 10.1 and one Mandrake 10.0. 

If you find my error, sorry for that. Anyway, thank you very much for your work. 

Milan Salek

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