Several months ago, I asked about False Northing/Eastings for the Albers
Equal Area Projection. GRASS currently doesn't allow the specification
of these items for this projection. Recently I was contacted by another
person who read my previous posting about this subject -- wondering if I
had a solution.
Anyway, a number of state agencies in California have standardised on an
Albers Equal Area Projection that has a false northing. There is quite
a bit of data available in this projection. Unfortunately, there's no
clean way to get this data into GRASS at the moment. I know the proj4
library supports this feature; so, I'm wondering if it would be possible
to implement it? I've been searching through the GRASS code base, but
am not familiar enough with it to know how all the projection code ties
together. I know there are many other things on the TODO list, but
perhaps someone familiar with the projection code could point me in the
right direction(s)?
Thanks.
--
Eric G. Miller <emiller@consrv.ca.gov>
Environmental Specialist
Office of Mine Reclamation
Hi Eric,
you can add support for false easting&northing for Alber's Equal Area in
GRASS5beta by editing the file src/libes/gis/geo_init.c. On line 35, just
after the last TABLE[AEA] definition, add the following lines:
TABLE[AEA][X0].ask = 1;
TABLE[AEA][X0].def_exists = 1;
TABLE[AEA][X0].deflt = 0.0;
TABLE[AEA][Y0].ask = 1;
TABLE[AEA][Y0].def_exists = 1;
TABLE[AEA][Y0].deflt = 0.0;
Then recompile.
regards
Morten Hulden
On Sun, 13 Aug 2000, Eric G . Miller wrote:
Several months ago, I asked about False Northing/Eastings for the Albers
Equal Area Projection. GRASS currently doesn't allow the specification
of these items for this projection. Recently I was contacted by another
person who read my previous posting about this subject -- wondering if I
had a solution.
Anyway, a number of state agencies in California have standardised on an
Albers Equal Area Projection that has a false northing. There is quite
a bit of data available in this projection. Unfortunately, there's no
clean way to get this data into GRASS at the moment. I know the proj4
library supports this feature; so, I'm wondering if it would be possible
to implement it? I've been searching through the GRASS code base, but
am not familiar enough with it to know how all the projection code ties
together. I know there are many other things on the TODO list, but
perhaps someone familiar with the projection code could point me in the
right direction(s)?
Thanks.
It's not that complicated. As Eric notes, the proj.4 library supports
false eastings and northing, and it's just a matter of getting the right
parameters in the PROJ_INFO file. (At least this is the case in GRASS 5.
I don't know about GRASS 4).
This is the projection file (the PROJ_INFO file in the
directory calif/PERMANENT) I use for the California Teale Albers
projection.
name: Albers Equal Area
proj: aea
ellps: clark66
a: 6378206.4000000004
es: 0.0067686580
lat_0: 0.0000000000
lat_1: 34.0000000000
lat_2: 40.5000000000
lon_0: -120.0000000000
y_0: -4000000
Best wishes,
Allan (another California GRASS user)
On Mon, 14 Aug 2000, Morten Hulden wrote:
Hi Eric,
you can add support for false easting&northing for Alber's Equal Area in
GRASS5beta by editing the file src/libes/gis/geo_init.c. On line 35, just
after the last TABLE[AEA] definition, add the following lines:
TABLE[AEA][X0].ask = 1;
TABLE[AEA][X0].def_exists = 1;
TABLE[AEA][X0].deflt = 0.0;
TABLE[AEA][Y0].ask = 1;
TABLE[AEA][Y0].def_exists = 1;
TABLE[AEA][Y0].deflt = 0.0;
Then recompile.
regards
Morten Hulden
On Sun, 13 Aug 2000, Eric G . Miller wrote:
> Several months ago, I asked about False Northing/Eastings for the Albers
> Equal Area Projection. GRASS currently doesn't allow the specification
> of these items for this projection. Recently I was contacted by another
> person who read my previous posting about this subject -- wondering if I
> had a solution.
>
> Anyway, a number of state agencies in California have standardised on an
> Albers Equal Area Projection that has a false northing. There is quite
> a bit of data available in this projection. Unfortunately, there's no
> clean way to get this data into GRASS at the moment. I know the proj4
> library supports this feature; so, I'm wondering if it would be possible
> to implement it? I've been searching through the GRASS code base, but
> am not familiar enough with it to know how all the projection code ties
> together. I know there are many other things on the TODO list, but
> perhaps someone familiar with the projection code could point me in the
> right direction(s)?
>
> Thanks.
>