[Proj] new 7 parameters

Markus Neteler neteler at itc.it
Sun Oct 22 13:33:59 EDT 2006

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
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
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

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
Parameters to be used are:
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
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,

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