> Am I correct in interpreting this post to mean that the pixel-is-area and > pixel-is-point tiffs >are read the exact same way by GDAL, with the only > difference being in the value of the >AREA_OR_POINT metadata key? Should > viewers then be looking for >the "AREA_OR_POINT" key in addition to the > georeferencing information, and shift the >display to center the top-left > pixel on (0,0) if it's set to Point?
That's my understanding, it's just a metadata tag there for use if you need it. I would say that viewers should only modify their behaviour from Area if they have the distinction for centre point vs. cell based views. I've seen it used to set centre-based TIN-like renderings, vs. cell-based image renderings - but there's nothing in the GDAL raster storage model that prevents you taking on either interpretation AFAIK, though the default is cell-based. (There can be a problem interpreting more flexible array formats like NetCDF, that can store irregularly spaced coordinate vectors for, say, the centres of cells on the X axis - and there's rarely any metadata (in the file) to say explicitly that it's centre- not corner-based. ) Cheers, Mike. On Tue, Jun 29, 2010 at 8:12 AM, Gillian WALTER <gwal...@mdacorporation.com> wrote: > Hi, > > I'm trying to wrap my head around Geotiff's AREA_OR_POINT=Area versus > AREA_OR_POINT=Point, and how that translates into GDAL. I've read the > "PixelIsPoint Raster Space" and "PixelIsArea Raster Space" sections of the > geotiff spec, and tried to find previous posts on the topic with very > limited success ( > http://osgeo-org.1803224.n2.nabble.com/GRASS-Problem-importing-geotiff-with-r-in-gdal-td1879130.html > ). Am I correct in interpreting this post to mean that the pixel-is-area > and pixel-is-point tiffs are read the exact same way by GDAL, with the only > difference being in the value of the AREA_OR_POINT metadata key? Should > viewers then be looking for the "AREA_OR_POINT" key in addition to the > georeferencing information, and shift the display to center the top-left > pixel on (0,0) if it's set to Point? > > Thanks, > > Gillian Walter > Software Developer > Geospatial Services Inc. > 57 Auriga Drive - Suite 201 > Ottawa, ON K2E 8B2 > Telephone: (613) 727-1087 #245 > Facsimile: (613) 727-5853 > Email: gwal...@mdacorporation.com > > This e-mail and any attachments are intended solely for the use of the > intended recipient(s) and may contain legally privileged, proprietary and/or > confidential information. Any use, disclosure, dissemination, distribution > or copying of this e-mail and any attachments for any purposes that have not > been specifically authorized by the sender is strictly prohibited. If you > are not the intended recipient, please immediately notify the sender by > reply e-mail and permanently delete all copies and attachments. The entire > content of this e-mail is for "information purposes" only and should not be > relied upon by the recipient in any way unless otherwise confirmed in > writing by way of letter or facsimile. > > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev > _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev