[GRASSLIST:8243] Re: problems in gnomonic projection

[Morten Hulden]

Milan Salek wrote:

> $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.

Shifted NS compared to what? Why are you expressing the shift in degrees 
though both spearfish60 (utm) and your gnom location are using meter units?

You use a spherical earth model in your PROJ_INFO. That could explain 
why you see unexpected NS values while EW is OK.

rgds
Morten