<br><div><span class="gmail_quote"></span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">-------- Message original --------<br>Sujet: [Gdal-dev] Nodata bitmasks / null processing
<br>Date: Sat, 04 Aug 2007 13:06:04 -0400<br>De: Frank Warmerdam <<a href="mailto:warmerdam@pobox.com">warmerdam@pobox.com</a>><br>Pour :: gdal-dev <<a href="mailto:gdal-dev@lists.maptools.org">gdal-dev@lists.maptools.org
</a>><br><br>Folks,<br><br>Currently GDAL supports two mechanisms for identifying nodata/transparent<br>areas in a raster. One is use of a particular pixel value as a nodata<br>value (returned by the GDALRasterBand::GetNodataValue() method) and the
<br>other<br>is by specifying an alpha band with alpha=0 marking transparent areas.<br><br>However, a number of file formats support a concept of "nodata masks" -<br>essentially bitmasks marking areas of the raster that are nodata areas. But
<br>this is accomplished without having to reserve a special marker value to be<br>the nodata value.<br></blockquote><div> </div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
I am looking for some feedback from the community. In particular I'm<br>interested in examples of file formats that include bit masking.</blockquote><div><br>Frank,<br><br>I'm not sure being able to say you what is the best way to implement this. But I can say that this is an interesting project. I can provide you a sample I would like to see implemented. MODIS HDF files are all provided with a Quality Assurance bit mask. For exemple you can take surface reflectance files (
<a href="http://edcdaac.usgs.gov/modis/myd09gqv5.asp">http://edcdaac.usgs.gov/modis/myd09gqv5.asp</a>, there is download links in this page). These files have two datasets for surface reflectance (<a href="http://edcdaac.usgs.gov/modis/myd09gqv5_sds.asp">
http://edcdaac.usgs.gov/modis/myd09gqv5_sds.asp</a>) and one for Quality Assurance (<a href="http://edcdaac.usgs.gov/modis/qa/myd09gq_qa_v5.asp">http://edcdaac.usgs.gov/modis/qa/myd09gq_qa_v5.asp</a>). I think that your project can be very usefull in this case.
<br><br>I hope this will help you !<br><br>Best regards,<br>Guillaume.<br></div></div>