Hi Carlos:
I georeferenced 2 screen shots of your maps and obtained good results.
I would have a close look at the coordinates of your ground control
points and make sure you selected the utm grid intersection as a control
point versus the corner of the mapsheet which is a lat/long grid. It is
easy to make a simple mistake
Kirk
On 5/17/2018 8:53 PM, Carlos Henrique Grohmann de Carvalho wrote:
Thanks for the input Nicolas
These are official maps so the utm grid is ok. I figured that I was
using a linear transformation, with the option to just create the
world file, which works for control points at the corners (lat/long),
since the boundaries of the map is defined by latitude/longitude. With
UTM, this simple transformation won't work, but TPS will give the
correct results.
Carlos
On Thu, May 17, 2018 at 7:28 PM, Nicolas Cadieux
<nicolas.cadi...@archeotec.ca <mailto:nicolas.cadi...@archeotec.ca>>
wrote:
Hi,
The utm grid is way off or we have the wrong epsg code. If you
geofence using 2 points (linear algo) using a service like google
earth, you will see the distortion. The long lat coordinate are
probably ok but I did not test them.
You can either use the long lat or use more points. With 4 points
and using the thin plate spline, I got good results.
Nicolas
Le 17 mai 2018 à 12:42, Carlos Henrique Grohmann de Carvalho
<carlos.grohm...@gmail.com <mailto:carlos.grohm...@gmail.com>> a
écrit :
Thanks Nicolas, but the misalignment still persists. OTF is off,
project has same CRS as data (epsg 29192). There is a ~400m
difference in the N-S direction.
Carlos
On Thu, May 17, 2018 at 1:28 PM, Nicolas Cadieux
<nicolas.cadi...@archeotec.ca
<mailto:nicolas.cadi...@archeotec.ca>> wrote:
Hi,
Disable projection on the fly. Make sure the project is in
the same CRS as your maps.
Nicolas
Le 17 mai 2018 à 12:14, Carlos Henrique Grohmann de Carvalho
<carlos.grohm...@gmail.com
<mailto:carlos.grohm...@gmail.com>> a écrit :
Hello all
I have two pngs of topographic maps from southeastern Brazil
(a zip file with images and points is available here:
https://www.dropbox.com/s/mexeh4be46pgsk6/images_georef.zip?dl=0
<https://www.dropbox.com/s/mexeh4be46pgsk6/images_georef.zip?dl=0>)
I'm trying to georeference them, but with partial success
only. In this image
(https://www.dropbox.com/s/37xxqp4fkwpdyqh/utm_error.png?dl=0
<https://www.dropbox.com/s/37xxqp4fkwpdyqh/utm_error.png?dl=0>)
you can see that the X coordinate is fine, but the Y
coordinate of the two maps won't match.
Both maps use South American Datum 1969. I selected points
near the edges, and used the UTM values.
Interestingly, if I use Lat/Long, and place the points at
the corners, using decimal degrees, the maps align perfectly.
Any help is appreciated
--
Prof. Carlos Henrique Grohmann
Institute of Energy and Environment - Univ. of São Paulo,
Brazil
- Digital Terrain Analysis | GIS | Remote Sensing -
http://carlosgrohmann.com <http://carlosgrohmann.com/>
http://orcid.org/0000-0001-5073-5572
<http://orcid.org/0000-0001-5073-5572>
________________
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Prof. Carlos Henrique Grohmann
Institute of Energy and Environment - Univ. of São Paulo, Brazil
- Digital Terrain Analysis | GIS | Remote Sensing -
http://carlosgrohmann.com <http://carlosgrohmann.com/>
http://orcid.org/0000-0001-5073-5572
<http://orcid.org/0000-0001-5073-5572>
________________
Can’t stop the signal.
--
Prof. Carlos Henrique Grohmann
Institute of Energy and Environment - Univ. of São Paulo, Brazil
- Digital Terrain Analysis | GIS | Remote Sensing -
http://carlosgrohmann.com <http://carlosgrohmann.com/>
http://orcid.org/0000-0001-5073-5572
________________
Can’t stop the signal.
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General Manager
Nortek Resource Solutions Inc.
RR # 1
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B0K 1W0
Tel (902) 922.3607
Email: k...@nortekresources.com
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