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Calibration question: how to deal with a slight rotation

 
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jvgoor



Joined: 07 Sep 2011
Posts: 42
Location: Maasland, The Netherlands

PostPosted: Wed Apr 18, 2012 12:23 pm    Post subject: Calibration question: how to deal with a slight rotation Reply with quote

In relation to my previous question. My small scale maps are slightly rotated (ie. 1 pixel off over 200-300 pixels). In a tool called Global Mapper I can set this straight, but then lines that where straight in the original image are getting messed up. As these are boxes with extra information that where present in the image, this looks not nice.
So I prefer to use the original image as this offers the best quality.

I have the acurate formulas and parameters to be able to relate any pixel to the right lat and long for the original picture. With this I can lay a grid of calibration points nicely spread over the whole map. As far as I can see this works fine and pixels (mouse) are correctly converted to the real latitude and longitude.

Is the cmBiquadraticPn calibration model the right way to deal with this?
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Jaap van Goor
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hlohning



Joined: 08 Sep 2006
Posts: 277
Location: Austria

PostPosted: Wed Apr 25, 2012 11:45 am    Post subject: Reply with quote

Hi Jaap,

using the biquadratic calibration model is the most general approach and works well in non-polar regions.

Another way to deal with rotated maps is to adjust the existing calibration by a rotation matrix, or even better, a Helmert transformation. The Helmert transformation is part of the upcoming release 10.1

Let me know, if you want to get a preview release.

Kind regards,

Hans
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Hans Lohninger
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jvgoor



Joined: 07 Sep 2011
Posts: 42
Location: Maasland, The Netherlands

PostPosted: Wed Apr 25, 2012 12:39 pm    Post subject: Rotated maps Reply with quote

Hi Hans,

With small scale maps the biquadratic calibration works quite well, although I have not tried plotting courses yet.

I would love to receive a review release but we are quite busy ourselves implementing all so I am afraid I would have not much time studying it very much.

Greetings,

Jaap
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