* Tomáš Brunclík <[email protected]> [2015-05-27 12:49:13 +0200]: > Hello all, > working with GRASS GIS 7.0.1svn (r65198) @Linux, I noticed, that when > importing two Landsat images from different dates, I often get them > spatially shifted to each other when comparing them in detail - meaning > when you zoom in to about 1:5000 scale and switch the viewed bands, the > features in the map jump by a fraction of pixel size. For Landsat 8 > images LC81910252013208 (reflectance product) and LC81910252013224 (DN > product) the shift is about 15m (half the pixel size) in both horizontal > and vertical direction. The same two products imported in GRASS 6.4.4 > have no visible shift at all and the corresponding pixels seem to be > perfectly aligned. > > The procedure to reproduce this: > > 1)Download and uncompress this archive (133 MB): > https://dl.dropboxusercontent.com/u/24062833/pixel_shift_208_224.zip > / > The archive contains band 5 of the two above mentioned Landsat scenes, > where the one with DOY 208 (the last number of the scene code, > day-of-year) is from surface reflectance (SR) product, the other with > DOY 224 is digital number (DN) product (I work on a script to > atmospherically correct DN product based on reference SR image)//.// > / > > 2) Start GRASS 7, create new mapset in location with UTM 33N > (EPSG:32633) spatial reference system. > > 3) Import each image, open them in the map, set colors, zoom in and > compare a distinct feature placement in detail: > > #import > r.in.gdal input="/path/to/data/LC81910252013208LGN00_sr_band5.tif" > output=208_grass7 > r.in.gdal input="/path/to/data/LC81910252013224LGN00_B5.TIF" > output=224_grass7 > > #set the null pixels of the DN band (helps the bands to get similar > color palette in the next step) > r.null map=224_grass7 setnull=0 > > #set colors: > r.colors map=208_grass7 > r.colors map=224_grass7 > > > 4) Zoom in to a distinct feature in about 1:5000 scale (I have used a > pond at coordinates 542365,554675), switch visibility of both images on, > then repeatedly switch on/off the upper image in the stack. You should > see the shift quite clearly. Zooming in even more, it is possible to > measure the shift. >
Tomas, I had a quick look. Pixels are perfectly aligned here (after going through all of the steps you mention here) in G7. Which version of GDAL are you on? Nikos [rest deleted] _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
