[GRASSLIST:8213] problems in gnomonic projection

[Milan Salek]

Hello all,

I have some difficulty with transformation from/to gnomonic projection which I 
found in 'my' area and repeated in Spearfish training dataset.

For example, 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 is an evident shift in NS (y) direction of about 20 minutes (20'). EW 
direction is OK. The same results were on other area in Europe and were the same 
when using v.proj.

In case the problem is between the keyboard and my chair I put the r.proj command:

GRASS 6.0.1 (spearfish_gnom):~ > r.proj input=elevation.dem location=spearfish 
mapset=PERMANENT output=elevation

I work on Mandrake 10.1, proj 4.4.9. The proj itself converts the projections OK.

Do you have any suggestion?

Best regards

Milan Salek