Enrico Graziani wrote:
Hello!
I'm trying to use imagery tools to georeference/rectify an image taken
from google earth...
Here's the procedure I've used without success:
- From GEarth saved image to a local file (jpeg) ( I've tried to
convert this jpeg to png but this didn't helped me. In both case I've
keeped the image as 24 bit...)
- Created a location wgs84 utm29 (North!) with region coordinate taken
from GEarth (in local format)
- Created a location xy in grass (6.2.3) with region as big as the picture
- Imported the image with g.in.gdal: this creates 3 raster maps, blue
green and red
- r.composite the 3 rasters to one "gearth" raster
- i.group to create group "group" containing the gearth raster
- i.target giving target the wgs84 utm29 location (mapset user)
- i.points to give 3 GCPs
(- tried also to run i.group to remove the gearth raster from
r.composite and add the 3 rgb rasters map)
- i.rectify -a group=group input=group extension=_rect order=1
Everything goes fine till here, except for the fact that if I add the
-c option to i.rectify it will always fail with "error while writing
to temp file".
However, when I go to other location the map doesn't display.
If I've rectified the 3 rgb rasters I can try to display the map with
an RGB layer or creating a single raster map with r.composite but,
first of all, it takes forever (running "top" while doing this
displayed a 99% of CPU use by d.rgb or r.composite) and, last but not
last, the map doesn't display. If I select on the map display "zoom to
selected map" it will zoom to default region (the selected region in
this location) even if I used i.rectify without the -c flag!
Worster if I try to rectify the "r.composite"d raster (the one
containing the 3 imported channel) first and then rectify it.
Everything goes ok but if I try to display it grass just stuck and I
need to restart the x server to quit the grass windows...
I had a look at the data in the wgs84_utm29 location and noticed that
this last "r.composite"d raster hasn't been "converted". Data in the
cell directory is around 24 kb and there is a 148 kb file in the
cell_misc/$RASTER_NAME directory .. starting jpeg was a couple of MBs..
Stranger in the other case (rectifying the 3 channels and then
displaying rgb layer or r.composite them): the files in the cell
directory are around 15 kb and 148 kb in the cell_misc folders, but
after r.composite, the raster coming from this has 6.9 MB in the cell
folder and 107.3 MB in the cell_misc folder of data.
All the files I'm talking about in the cell misc folder are called
"null" and dolphin recognized them by the MIME type as jpeg2000, but
gwenview isn't able to display them...
My configuration is the installation of the GRASS Live DVD coming from
the Trento University in a VMWare machine running with VMPlayer 2.0.5
on Debian Etch.
This live should be Kubuntu Hardy ( ?) based.
------------------------------------------------------------------------
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For a quick georeferencing, with just 3 gcps, you can just use gdal.
gdal_translate -a_srs "EPSG:4326" -of GTiff -gcp x1 y1 X1 Y1 -gcp x2 y2
X2 Y2 -gcp x3 y3 X3 Y3 gearth.jpg gearth.tif
gdalwarp -t_srs "EPSG:4326" -rc gearth.tif gearth_rectified.tif
Then load the image with r.in.gdal.
You can get the gcps by hovering the mouse over landmarks in The Gimp
(x,y) and Google Earth (X,Y).
You can find the EPSG code for your utm region here:
http://www.epsg-registry.org/
Cheers
John
--
Dr John Stevenson
Postdoctoral Research Associate
School of Earth, Atmospheric and Environmental Sciences
Williamson Building (Room 2.42)
University of Manchester
Manchester M13 9PL, UK
tel. +44(0)161 306 6585; fax. +44(0)161 306 9361;
[email protected]
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