Hi,
I have a question if we want to extend the Transverse Mercator
definition mode (g.setproj etc.) by false northing?
It seem that the UK needs the x_0 to be defined:
http://www.geocities.com/mapref/prj/uk/uk_osbg36.html
Also strange local map projections as found in Bolzano, Italy,
need false northing for Transverse Mercator.
If there are no objections, I would add it to
src/libes/gis/geo_init.c
Markus
Markus Neteler wrote:
Hi,
I have a question if we want to extend the Transverse Mercator
definition mode (g.setproj etc.) by false northing?
It seem that the UK needs the x_0 to be defined:
Do you mean y_0?
It is x_0 : +400000
y_0 : -100000
for BNG. So yes that would be handy.
David
http://www.geocities.com/mapref/prj/uk/uk_osbg36.html
Also strange local map projections as found in Bolzano, Italy,
need false northing for Transverse Mercator.If there are no objections, I would add it to
src/libes/gis/geo_init.cMarkus
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On Wed, Mar 06, 2002 at 06:45:25PM +0000, David D Gray wrote:
Markus Neteler wrote:
> Hi,
>
> I have a question if we want to extend the Transverse Mercator
> definition mode (g.setproj etc.) by false northing?
> It seem that the UK needs the x_0 to be defined:
>Do you mean y_0?
Yes, of course: y_0!
It is x_0 : +400000
y_0 : -100000for BNG. So yes that would be handy.
O.k, then I'll change that.
Markus
> http://www.geocities.com/mapref/prj/uk/uk_osbg36.html
>
> Also strange local map projections as found in Bolzano, Italy,
> need false northing for Transverse Mercator.
>
> If there are no objections, I would add it to
> src/libes/gis/geo_init.c
>
> Markus
>
> _______________________________________________
> grass5 mailing list
> grass5@grass.itc.it
> http://grass.itc.it/mailman/listinfo/grass5
>
>_______________________________________________
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Speaking about updating projection definitions, I have noticed that
lcc (Lambert Conformal conic) doesn't have false easting or northing
(at least when using g.setproj). On the other hand, France will now
use a new system (Lambert 93) based on GRS80 ellispoid, instead of
the old one (a familly of lcc projections) based on Clarke 1880
ellipsoid (IGN modified). This has lead to a conversion grid for
precise transformation (something like NAD27/NAD83).
Since proj has the ability to use such a grid, it sounds relatively
easy to incorporate french geodetic systems. All the détails
parameters, formulas and algorithms can be found (in french 
at
http://www.ign.fr/fr/PI/activites/geodesie/rgf93/OUTILS/index.html
--
Michel WURTZ - DIG - Maison de la télédétection
500, rue J.F. Breton
34093 MONTPELLIER Cedex 5
Hi again,
I have update the CVS to also query for false northing in
transverse mercator:
E.g.:
[...]
Enter Central Parallel [lat_0] (23N) :0N
Enter Central Meridian [lon_0] (96W) :9E
Enter Scale Factor at the Central Meridian [k_0] [1.0000000000]:
Enter False Easting [x_0] [0.0000000000]:
Enter False Northing [y_0] [0.0000000000]:
Enter plural form of units [meters]:
[...]
Now it should be easy to define the British NG.
Cheers
Markus
PS: Recompile libgis and the modules in src/general/
On Wed, Mar 06, 2002 at 06:45:25PM +0000, David D Gray wrote:
Markus Neteler wrote:
> Hi,
>
> I have a question if we want to extend the Transverse Mercator
> definition mode (g.setproj etc.) by false northing?
> It seem that the UK needs the x_0 to be defined:
>Do you mean y_0?
It is x_0 : +400000
y_0 : -100000for BNG. So yes that would be handy.
David
> http://www.geocities.com/mapref/prj/uk/uk_osbg36.html
>
> Also strange local map projections as found in Bolzano, Italy,
> need false northing for Transverse Mercator.
>
> If there are no objections, I would add it to
> src/libes/gis/geo_init.c
>
> Markus
>
> _______________________________________________
> grass5 mailing list
> grass5@grass.itc.it
> http://grass.itc.it/mailman/listinfo/grass5
>
>_______________________________________________
grass5 mailing list
grass5@grass.itc.it
http://grass.itc.it/mailman/listinfo/grass5
On Thu, Mar 07, 2002 at 09:42:18AM +0000, Michel Wurtz wrote:
Speaking about updating projection definitions, I have noticed that
lcc (Lambert Conformal conic) doesn't have false easting or northing
(at least when using g.setproj).
That is surprising: in geo_init.c is defined:
TABLE[LCC][LAT0].ask = 1;
TABLE[LCC][LAT0].def_exists = 1;
TABLE[LCC][LAT0].deflt = 23.0;
TABLE[LCC][LON0].ask = 1;
TABLE[LCC][LON0].def_exists = 1;
TABLE[LCC][LON0].deflt = -96.0;
TABLE[LCC][LAT1].ask = 1;
TABLE[LCC][LAT1].def_exists = 1;
TABLE[LCC][LAT1].deflt = 33.0;
TABLE[LCC][LAT2].ask = 1;
TABLE[LCC][LAT2].def_exists = 1;
TABLE[LCC][LAT2].deflt = 45.0;
TABLE[LCC][X0].ask = 1;
TABLE[LCC][X0].def_exists = 1;
TABLE[LCC][X0].deflt = 0.0;
TABLE[LCC][Y0].ask = 1;
TABLE[LCC][Y0].def_exists = 1;
TABLE[LCC][Y0].deflt = 0.0;
So it should ask for x_0 and y_0. Obviously there is another
test somewhere to suppress that?
On the other hand, France will now
use a new system (Lambert 93) based on GRS80 ellispoid, instead of
the old one (a familly of lcc projections) based on Clarke 1880
ellipsoid (IGN modified). This has lead to a conversion grid for
precise transformation (something like NAD27/NAD83).
Since proj has the ability to use such a grid, it sounds relatively
easy to incorporate french geodetic systems. All the détails
parameters, formulas and algorithms can be found (in frenchhttp://www.ign.fr/fr/PI/activites/geodesie/rgf93/OUTILS/index.html
This sounds like a datum transform...
Markus
On Thu, 7 Mar 2002, Markus Neteler wrote:
PS: Recompile libgis and the modules in src/general/
if you want m.proj to become aware of the changes you have to recompile
sre/misc/m.proj as well.
Morten Hulden