[GRASS5] Re: Helping creating a Portuguese location in GRASS

GRASS GRASS developer
1

(cc grass5)

Here a forwarded question which reached me recently for the
projection experts.

M.

On Tue, Apr 08, 2003 at 12:39:10PM +0100, Miguel Repas wrote:

Dear Markus,

My appologies for reaching personally with this question. I have been
searching for a solution to my problem in the grass site, the discussion
list and in your book but without success. I am new to GRASS and I am
struggling to getting my data on it. I sincerely hope you could help me
on this.

My data is in the so-called portuguese military system. It is defined as
a gauss kruger projection, international (hayford) elipsoid. The
coordinates are rectangular with a central point at Melrica (most of my
data has a false easting of 200km and a false northing of 300km). Lisbon
datum. I need to import this data to grass and later to put it in a new
UTM ED50 location.

I have recently found this string which I believe specifies the
parameters for my data:

PROJCS["Portuguese_National_Grid",GEOGCS["GCS_Lisbon_Lisbon",DATUM["D_Li
sbon",SPHEROID["International_1924",6378388,297]],PRIMEM["Lisbon",-9.131
906111111112],UNIT["Degree",0.017453292519943295]],PROJECTION["Transvers
e_Mercator"],PARAMETER["False_Easting",200000],PARAMETER["False_Northing
",300000],PARAMETER["Central_Meridian",1],PARAMETER["Scale_Factor",1],PA
RAMETER["Latitude_Of_Origin",39.66666666666666],UNIT["Meter",1]]

How can I create a location based on these parameters?
Can I later project this data to UTM ED50 within grass? How?

I most sincerly appreciate your help.
Cheers
Miguel Repas

2

On Tue, Apr 08, 2003 at 12:39:10PM +0100, Miguel Repas wrote:
>
> My data is in the so-called portuguese military system. It is defined as
> a gauss kruger projection, international (hayford) elipsoid. The
> coordinates are rectangular with a central point at Melrica (most of my
> data has a false easting of 200km and a false northing of 300km). Lisbon
> datum. I need to import this data to grass and later to put it in a new
> UTM ED50 location.
>
> I have recently found this string which I believe specifies the
> parameters for my data:
>
> PROJCS["Portuguese_National_Grid",GEOGCS["GCS_Lisbon_Lisbon",DATUM["D_Li
> sbon",SPHEROID["International_1924",6378388,297]],PRIMEM["Lisbon",-9.131
> 906111111112],UNIT["Degree",0.017453292519943295]],PROJECTION["Transvers
> e_Mercator"],PARAMETER["False_Easting",200000],PARAMETER["False_Northing
> ",300000],PARAMETER["Central_Meridian",1],PARAMETER["Scale_Factor",1],PA
> RAMETER["Latitude_Of_Origin",39.66666666666666],UNIT["Meter",1]]

There are details of the various Portuguese systems at
http://crs.ifag.de/country_select.php?country=PT

All you need to do is run g.setproj (it is run automatically if you select
to create a new location in GRASS) and enter the parameters when prompted.
You won't need to specify a datum as your two locations are referenced to
the same ellipsoid so you may simply re-project between the two. The only
awkward thing I can see that g.setproj will ask you is the Central
Meridian, which is given as 1 degree in your metadata above but that is
relative the Lisbon Prime Meridian whereas GRASS uses Greenwich, so you need
to add these two together to give -8.131... (above).

The above webpage gives the exact parameter as 8:07:54.862W and the other
one is 39:40:00N

I tried this and your PROJ_INFO file (view it using g.projinfo) should
look something like this (without the datum parameters although they
should do no harm):

name: Transverse Mercator
datum: ptdlx
datumparams: towgs84=-282.1,-72.2,120.0,-1.592,0.145,-0.890,-4.46
proj: tmerc
ellps: international
a: 6378388.0000000000
es: 0.0067226700
f: 297.0000000000
lat_0: 39.6666666667
lon_0: -8.1319061111
k_0: 1.0000000000
x_0: 200000.0000000000
y_0: 300000.0000000000

>
> How can I create a location based on these parameters?
> Can I later project this data to UTM ED50 within grass? How?

Set up a separate location using UTM (you need to know which zone) and the
eur50 ellipsoid and then use r.proj, v.proj or s.proj to re-project your
data depending on if it is raster, vector or sites data.