[Proj] new 7 parameters

[Markus Neteler]

On Sat, Oct 21, 2006 at 07:41:47PM +0200, massimodisasha wrote:
> hi,
> i've 45 point of the (igm95) national italian grid of double points  
> in (wgs84 - gauss boaga R40)
> (IGM is the italian's geographical military institute)
> 
> all my points are distribuited in a small italian region.
> 
> i've done a little algoritms in matlab language  for resolve the  
> Helmert linear sistem....
> ...now i've a new set of 7 parameters for do a trasformation beetween  
> WGS and GB-R40.
> 
> how can i use this new parameters in Grass ?

When you define a new "location" (GRASS project), then
select 
D Other projection
to go into the user defined dialog.

Then select

Please specify projection name
Enter 'list' for the list of available projections
Hit RETURN to cancel request
>tmerc
Do you wish to specify a geodetic datum for this location?(y/n) [y]

Please specify datum name
Enter 'list' for the list of available datums
or 'custom' if you wish to enter custom parameters
Hit RETURN to cancel request
>custom                                 <<<<--- !!

Please specify ellipsoid name
Enter 'list' for the list of available ellipsoids
Hit RETURN to cancel request
>international

Please specify datum transformation parameters in PROJ.4 syntax. Examples:
        towgs84=dx,dy,dz        (3-parameter transformation)
        towgs84=dx,dy,dz,rx,ry,rz,m     (7-parameter transformation)
        nadgrids=alaska (Tables-based grid-shifting transformation)
Hit RETURN to cancel request
>towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68
Parameters to be used are:
"towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68"
Is this correct?(y/n) [y]

Enter Scale Factor at the Central Meridian  [1.0000000000]: 0.9996
[...]



> can i use it in the (r.proj/v.proj) grass command?

Like this r.proj/v.proj use the datum.

Shortcut: If you want to modify an existing location (not
sure if that's a good idea since your data need to be reprojected),
simply edit
grassdata/<location>/PERMANENT/PROJ_INFO
and substitute the old datum parameters with

datum: rome40
datumparams: towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68

My PROJ_INFO looks like this:
name: Transverse Mercator
datum: rome40
datumparams: towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68
proj: tmerc
ellps: international
a: 6378388.0000000000
es: 0.0067226700
f: 297.0000000000
lat_0: 0.0000000000
lon_0: 9.0
k_0: 0.9996000000
x_0: 1500000.0000000000

Hope this helps,
Markus