Dne 27.5.2015 v 18:43 Nikos Alexandris napsal(a):
* 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]
Hello,
I have GDAL 1.6.3 in GRASS 7, GDAL 1.10.1 in GRASS 6. Could it be it? Is
the GDAL part of the binary snapshot download, or does it uses one
already on my system? My GRASS 7 is binary snapshot download, GRASS 6 is
installed from Debian packages coming from my distro repository.
Tried again with newly created location and mapset, the same result.
Tomas
My GRASS 7 details:
Verze GRASSu: 7.0.1svn
Revize SVN GRASSu:: 65198
Datum sestavení: 2015-05-09
Platforma sestavení: x86_64-unknown-linux-gnu
GDAL/OGR: 1.6.3
PROJ.4: 4.7.0
GEOS: 3.2.0
SQLite: 3.7.13
Python: 2.7.5+
wxPython: 3.0.1.1
Platforma: Linux-3.11-2-amd64-x86_64-with-LinuxMint-1-debian
My GRASS 6 details:
GRASS version: 6.4.4
GRASS SVN Revision:
GDAL/OGR: 1.10.1
PROJ4: Rel. 4.8.0, 6 March 2012
Python: 2.7.5+
wxPython: 3.0.1.1
Platform: Linux-3.11-2-amd64-x86_64-with-LinuxMint-1-debian
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