Hi,
I’m having issues with projections in GRASS. I have two co-located projects, one in UTM projection, the other in an Oblique Mercator (omerc). The problem I’m having is when I query the rotated Hotine projection with “d.where -w”, the returned Lat, Lon is nonsensical. However, geotiffs exported from this GRASS project display correctly in Global Mapper with other geotiffs from different projections. So something appears wrong with “d.where -w”.
If Global Mapper is clever enough to deal with the coordinate conversion, then I think GRASS should be able to deal with this.
Garret
I'm having issues with projections in GRASS. I have two co-located
projects, one in UTM projection, the other in an Oblique Mercator
(omerc). The problem I'm having is when I query the rotated Hotine
projection with "d.where -w", the returned Lat, Lon is nonsensical.
However, geotiffs exported from this GRASS project display correctly in
Global Mapper with other geotiffs from different projections. So
something appears wrong with "d.where -w".
If I'm not mistaken, I think you need to have "to_WGS84" parameter shifts
defined for your location for the -w flag in d.where to work properly. Can
you post the output of g.proj -pd?
~ Eric.
GRASS 6.2.2 (Margaretsville_rotated):~ > g.proj -pd
-PROJ_INFO-------------------------------------------------
name : Oblique Mercator
datum : wgs84
towgs84 : 0.000,0.000,0.000
proj : omerc
ellps : wgs84
a : 6378137.0000000000
es : 0.0066943800
f : 298.2572235630
lat_0 : 35.0000000000
lat_1 : -20.0000000000
lat_2 : 20.0000000000
lon_0 : 20.0000000000
lon_1 : -120.0000000000
lon_2 : -60.0000000000
k_0 : 1.0000000000
no_rot : defined
no_uoff : defined
rot_conv : defined
-PROJ_UNITS------------------------------------------------
unit : meter
units : meters
meters : 1.0
GRASS datum code: wgs84
WKT Name: WGS_1984
Datum transformation parameters (PROJ.4 format):
towgs84=0.000,0.000,0.000
GRASS 6.2.2 (Margaretsville_rotated):~ >
-----Original Message-----
From: Patton, Eric
Sent: 4 February, 2008 1:02 PM
To: Duffy, Garret; grass-dev@grass.itc.it
Subject: RE: [GRASS-dev] d.where -w problem
I'm having issues with projections in GRASS. I have two co-located
projects, one in UTM projection, the other in an Oblique Mercator
(omerc). The problem I'm having is when I query the rotated Hotine
projection with "d.where -w", the returned Lat, Lon is nonsensical.
However, geotiffs exported from this GRASS project display correctly in
Global Mapper with other geotiffs from different projections. So
something appears wrong with "d.where -w".
If I'm not mistaken, I think you need to have "to_WGS84" parameter
shifts defined for your location for the -w flag in d.where to work
properly. Can you post the output of g.proj -pd?
~ Eric.
GRASS 6.2.2 (Margaretsville_rotated):~ > g.proj -pd
-PROJ_INFO-------------------------------------------------
name : Oblique Mercator
datum : wgs84
towgs84 : 0.000,0.000,0.000
proj : omerc
ellps : wgs84
a : 6378137.0000000000
es : 0.0066943800
f : 298.2572235630
lat_0 : 35.0000000000
lat_1 : -20.0000000000
lat_2 : 20.0000000000
lon_0 : 20.0000000000
lon_1 : -120.0000000000
lon_2 : -60.0000000000
k_0 : 1.0000000000
no_rot : defined
no_uoff : defined
rot_conv : defined
-PROJ_UNITS------------------------------------------------
unit : meter
units : meters
meters : 1.0
GRASS datum code: wgs84
WKT Name: WGS_1984
Datum transformation parameters (PROJ.4 format):
towgs84=0.000,0.000,0.000
GRASS 6.2.2 (Margaretsville_rotated):~ >
That's strange...I don't know what's happening with d.where; if no one else chimes in with an idea, I would file a bug report about it.
~ Eric.