[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
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
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