Re: [GRASS-user] Problem with g.region in lat-lon projection
John A Stevenson wrote: Hi, I am trying to set up a grid with a specified resolution using g.region. The information about the grid that came with the data that I want to plot is: X grid origin: 0.2812500 Y grid origin: -89.81250 X grid size: 640 Y grid size: 480 X grid resolution: 0.5625000 Y grid resolution: 0.375 I set up the grid with the following command: GRASS 6.4.1 (global_ll_wgs84):~/NAME/G2011 g.region w=0.2812500 s=-89.81250 cols=640 rows=480 ewres=0.562500 nsres=0.375 I would expect this grid to cover the whole globe (e.g. 640*0.5625=360), but instead it just generates a thin strip, and the ewres is too small. GRASS 6.4.1 (global_ll_wgs84):~/NAME/G2011 g.region -p projection: 3 (Latitude-Longitude) zone: 0 datum: wgs84 ellipsoid: wgs84 north: 74N south: 89:48:45S west: 0:16:52.5E east: 24E nsres: 0:20:28.59375 ewres: 0:02:13.417969 rows: 480 cols: 640 cells: 307200 Where am I going wrong? I think GRASS prefers to have all the extents n,s,e,w and either rows/cols or resolution to calculate a region. With the information available, North = -89.81250 + 480 * 0.375 = 90.1875 Interestingly, the North deviation from 90N and the South deviation from 90S is 0.1875 = 0.375 / 2, half a cell East = 0.2812500 + 640 * 0.5625 = 360.28125 Interestingly, the East deviation from 360E and the West deviation from 0 is 0.28125 = 0.5625 / 2, half a cell It is therefore possible that the true region extents are n=90 s=-90 w=0 e=360 and that X and Y grid origin refer to the center, not the corner of the lower left cell. This should work: g.region n=90 s=-90 w=0 e=360 rows=480 cols=640 -p and r.region map=my_map n=90 s=-90 w=0 e=360 Markus M ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] Problem with g.region in lat-lon projection
Hi, I am trying to set up a grid with a specified resolution using g.region. The information about the grid that came with the data that I want to plot is: X grid origin:0.2812500 Y grid origin:-89.81250 X grid size: 640 Y grid size: 480 X grid resolution:0.5625000 Y grid resolution:0.375 I set up the grid with the following command: GRASS 6.4.1 (global_ll_wgs84):~/NAME/G2011 g.region w=0.2812500 s=-89.81250 cols=640 rows=480 ewres=0.562500 nsres=0.375 I would expect this grid to cover the whole globe (e.g. 640*0.5625=360), but instead it just generates a thin strip, and the ewres is too small. GRASS 6.4.1 (global_ll_wgs84):~/NAME/G2011 g.region -p projection: 3 (Latitude-Longitude) zone: 0 datum: wgs84 ellipsoid: wgs84 north: 74N south: 89:48:45S west: 0:16:52.5E east: 24E nsres: 0:20:28.59375 ewres: 0:02:13.417969 rows: 480 cols: 640 cells: 307200 Where am I going wrong? John -- Dr John A Stevenson RSE/Scottish Government Personal Research Fellow (co-funded by Marie Curie Actions) School of GeoSciences The University of Edinburgh Grant Institute West Mains Road Edinburgh EH9 3JW Scotland PHONE: (+44) 131 650 7526 FAX: (+44) 131 668 3184 email: john.steven...@ed.ac.uk web: http://www.geos.ed.ac.uk/homes/jsteven5 blog: http://all-geo.org/volcan01010 The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Problem with g.region in lat-lon projection
On 28/11/11 13:23, John A Stevenson wrote: Hi, I am trying to set up a grid with a specified resolution using g.region. The information about the grid that came with the data that I want to plot is: X grid origin: 0.2812500 Y grid origin: -89.81250 X grid size: 640 Y grid size: 480 X grid resolution: 0.5625000 Y grid resolution: 0.375 I set up the grid with the following command: GRASS 6.4.1 (global_ll_wgs84):~/NAME/G2011 g.region w=0.2812500 s=-89.81250 cols=640 rows=480 ewres=0.562500 nsres=0.375 I would expect this grid to cover the whole globe (e.g. 640*0.5625=360), but instead it just generates a thin strip, and the ewres is too small. If you have existing settings for e and n, it will keep those. You have to use g.region -d to reset to default values (assuming your default values are -180 - 180 -90 - 90). However, I think that g.region maxes out at 180E and 90N. When I use your settings, I get the following: GRASS 6.4.1 (LLWGS84):~ g.region -d w=0.2812500 s=-89.81250 cols=640 rows=480 ewres=0.562500 nsres=0.375 -p projection: 3 (Latitude-Longitude) zone: 0 datum: wgs84 ellipsoid: wgs84 north: 90N south: 89:48:45S west: 0:16:52.5E east: 180E nsres: 0:22:28.59375 ewres: 0:16:50.917969 rows: 480 cols: 640 cells: 307200 or by aligning to resolution: GRASS 6.4.1 (LLWGS84):~ g.region -d w=0.2812500 s=-89.81250 cols=640 rows=480 ewres=0.562500 nsres=0.375 -pa projection: 3 (Latitude-Longitude) zone: 0 datum: wgs84 ellipsoid: wgs84 north: 90N south: 90S west: 0 east: 180E nsres: 0:22:30 ewres: 0:16:52.5 rows: 480 cols: 640 cells: 307200 i.e. it adapts the resolution in order to get 640 columns between 0W and 180E. Moritz ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Problem with g.region in lat-lon projection
John wrote: I am trying to set up a grid with a specified resolution using g.region. The information about the grid that came with the data that I want to plot is: X grid origin: 0.2812500 Y grid origin: -89.81250 X grid size: 640 Y grid size: 480 X grid resolution: 0.5625000 Y grid resolution: 0.375 I set up the grid with the following command: ... dumb question: does this work? r.info your_imported_map g.region rast=your_imported_map do you know if the original data used the cell- center registered or grid line-confluence registered convention? Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
