> -------- Original Message -------- > Subject: Can I use MrSID files in Xastir? > Date: Wed, 01 Apr 2009 14:16:29 -0500 > From: Jim Tolbert <[email protected]> > To: XASTIR <[email protected]> > > > > Hi, all........... > > I have access to the aerial photos of our county. They are in MrSid > format (Multi resolution Seamless Image Database) and are used in the > Arcview system by the county land information department. The mapping > technician tried to output it a few times, but got no where.
No, you can't use MrSID format images directly in Xastir. You *can* possibly get a MrSID SDK to link in with GDAL, and use gdal_translate to pull them in to regular GeoTIFF format. Last time I checked, though, Lizardtech's SDK for Linux was so old you couldn't link it to GDAL with any current generation version of GCC. If anyone had ever followed through on the promise to support GDAL rasters in Xastir, then having the MrSID SDK linked in with GDAL, and building Xastir with GDAL support would have covered this situation, but then again if we had some ham we could have ham and eggs if we had some eggs. On the upside, you can usually use the free tool from Lizardtech called "mrsiddecode" to uncompress the images into GeoTIFF format. I've done this with some of our county's high-res aerial photos and it usually works well. On occasion, though, I've had the durned mrsiddecode tool simply segfault on an image with no path forward. Sometimes, too, the mrsiddecode tool doesn't properly georeference the GeoTIFF file and you have to make it produce a TFW file, then use gdal_translate with that TFW file to produce a properly georeferenced file. I haven't figured out why it does that sometimes. It could be related to how the MrSID file was produced (or what tool was used to produce it). Be warned: MrSID is a *phenomenally* efficient compression algorithm. Once you use mrsiddecode or gdal_translate to make a GeoTIFF file that Xastir can use, the file might easily be 50 times larger than the original. High-res aerial photos tend to produce *enormous* GeoTIFF files, even when you remember to specify options to enable PACKBITS compression on the Tiff file. This fact is what pretty much prevents me from bothering most of the time. Oh --- the other thing that bites you is that usually the GeoTIFF you get will be an RGB image (three bands) which Xastir also can't use directly. You then have to dither the thing into a 1-band colormapped file. You can do this pretty easily with the GDAL tool rgb2pct (Red Green Blue to PseudoColorTable). This will decrease the file size somewhat, but it'll still be enormous. You might want to invest in a terrabyte USB drive or two if you're gonna make a sizable collection of these images. -- Tom Russo KM5VY SAR502 DM64ux http://www.swcp.com/~russo/ Tijeras, NM QRPL#1592 K2#398 SOC#236 http://kevan.org/brain.cgi?DDTNM In some cultures what I do would be considered normal. -- Ineffective daily affirmation -- Tom Russo KM5VY SAR502 DM64ux http://www.swcp.com/~russo/ Tijeras, NM QRPL#1592 K2#398 SOC#236 http://kevan.org/brain.cgi?DDTNM In some cultures what I do would be considered normal. -- Ineffective daily affirmation _______________________________________________ Xastir mailing list [email protected] http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
