Re: [GRASS-user] how to calculate areas
to my mind, one has to be cautious with this module, and be aware of how surfaces are estimated. It appears that results show a big variability given the current region resolution. (just try r.surf.area on a sloppy plane [generated with r.plane], knowing its inclination and thus its actual surface in advance) Bye, Vincent Le mardi 16 septembre 2008 à 02:28 -0700, Alex Mandel a écrit : Alex Mandel wrote: Maciej Tomaszczyk wrote: hello I have DEM of some part of mountains chain and i would like to calculate a real area of this (area in 3d not plane area). I wonder if Grass can do it. best maciej Maciej Tomaszczyk Polish Geological Institute Geological Mapping Department http://www.pgi.gov.pl http://www.opengeology.pl Just to clarify, you mean surface area as opposed to footprint of the mountain range. So the sum of all the surfaces of the 3d model? Alex The solution to that problem would be r.surf.area which should give you both the 2D and 3D area. You'll have to actually try this as I just read about it in Markus and Helena's book. Alex ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Trouble with ESRI TIGER/LINE Files and Coordinate System
Ugh. The LINESTRINGs contain the weird coordinates (in the 10s), not raw lat/lon. Extent: (-59948.354015, -457156.354302) - (51189.384222, -322776.485268) QGIS also uses the weird coordinates as well. gvSIG did as well, until I changed the measurement unit to degree. It's GUI for map display is very similar to QGIS. Is there a such thing switching measurement units to degrees in GRASS? ;-) Unfortunately, there is no PRJ file with these shapefiles, which is really frustrating. The website claims they are NAD83 lat/lon decimal degrees. My region should be 119W to 121W and 34N to 36N. Could these be UTM coordinates?? R. hamish_b wrote: can you check with ogrinfo what's *really* in the shapefile? ogrinfo -ro -al mapname.shp That will dump a huge amount of stuff to the terminal (^C to kill it) but you should see LINESTRING with a comma separated list of coordinates. Are those raw coordinates in lat/lon or ...? what does the shapefile.prj look like? I am not too familiar with gvSIG's capabilities; will QGIS load it and show correct projection info and mouse-over coords on the bottom status line? Hamish -- View this message in context: http://www.nabble.com/Trouble-with-ESRI-TIGER-LINE-Files-and-Coordinate-System-tp19506319p19515581.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
