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<TITLE>Re: [GRASS-user] problem displaying imported, rectified raster images</TITLE>
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<FONT FACE="Verdana, Helvetica, Arial"><SPAN STYLE='font-size:12.0px'>Try the new georectifying module in GRASS 6.3 from William Kyngesbury’s Grass for Mac site (find from the GRASS downloads page).<BR>
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Note: if using the new georectifying module, you START the georectifying session in the location/mapset you want the image to end up in, rather than the xy location/mapset where the unrectified image is stored (the procedure for i.points).<BR>
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Michael<BR>
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On 5/8/07 11:39 AM, "pete davidson" <caitifty@gmail.com> wrote:<BR>
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</SPAN></FONT><BLOCKQUOTE><FONT FACE="Verdana, Helvetica, Arial"><SPAN STYLE='font-size:12.0px'>Hi all<BR>
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I've been struggling with this problem for days.. I'm trying to import a scanned map into grass 6.1.0 on a mac. All seems to go well, until I try and display the final raster. Here's the steps I've taken, and thing's I've tried. <BR>
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Many thanks in advance for any suggestions or advice for resolving what I suspect is a total newbie question<BR>
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Pete<BR>
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- create a new xy region<BR>
- import the image (a png scanned at 300dpi) using r.in.gdal input=[path to scanned file] output=TL0232 location=scanTL0232 <BR>
- exit grass, re-launch and use region scanTL0232/PERMANENT<BR>
- i.target group=TL0232 location=[real_location] mapset=PERMANENT (where 'real_location' is a pre-existing NAD83 region I want to use this raster in) <BR>
- d.mon x0<BR>
- d.rast TL0232_blue (as a quick test that the image imported correctly, and yes, I'm looking at a nice, high resolution image)<BR>
- i.points TL0232 (note that contra several of the online guides, r.in.gdal automatically created a group, so I didn't need to run i.group first)<BR>
- select a bunch of reference points, giving real-world eastings & northings, then quit i.points<BR>
- i.rectify -a group=TL0232 extension=_1 order=1 <BR>
- exit grass, re-launch and use region [real_location]/PERMANENT<BR>
- d.mon x0<BR>
- d.rast TL0232.blue_1<BR>
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What I now get is a super-low res image: 6 or 7 giant pixels to a side. If I display other pre-existing vector layers (eg a tiger line street map), the raster has clearly been located correctly within the region, with the orientation and relative size I'd expect. <BR>
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For several days I assumed I was making a mistake somewhere in the r.in.gdal / i.target / i.points / i.rectify process. However, this morning I opened qgis to do something else, then on a whim created a new map, displayed a couple of pre-existing vector layers from the grass 'real_location' location, then added the grass raster layer TL0232.blue_1. To my surprise it displayed perfectly. Correctly oriented and rectified and in a usable resolution and everything. <BR>
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Back in grass, if I do<BR>
- g.region rast=TL0232.blue_1<BR>
- d.mon x0<BR>
- d.rast TL0232.blue_1<BR>
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I get a correctly displayed raster, however as soon as I do g.region -d to go back to the (larger) default region, any attempt to display the raster again produces an unusably low-res version..<BR>
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So.. What am I doing wrong? Any suggestions? Thanks again.<BR>
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__________________________________________<BR>
Michael Barton, Professor of Anthropology<BR>
School of Human Evolution & Social Change <BR>
Center for Social Dynamics & Complexity<BR>
Arizona State University<BR>
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phone: 480-965-6213<BR>
fax: 480-965-7671<BR>
www: <a href="http://www.public.asu.edu/~cmbarton">http://www.public.asu.edu/~cmbarton</a> <BR>
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