gvSIG bugs #3006

Gerroreferencing tool RMS seems not working properly

Added by Manuel Madrid over 9 years ago. Updated over 9 years ago.

Status:Invalid% Done:

0%

Priority:NormalSpent time:-
Assignee:-
Category:Raster
Target version:-
Severity:Minor Add-on version:
gvSIG version:2.1.0 Add-on build:
gvSIG build:2254 Add-on resolve version:
Operative System:Linux Add-on resolve build:
Keywords: Proyecto:
Has patch: Hito:
Add-on name:Unknown

Description

1. Start georeferencing and image with reference cartography and afin transformation options.
2. Place three control points.
3. Check the RMS value.
4. Now move one of the control points hundred of meters away from the original place.
5. Check that the RMS value keeps very low, which is not correct.

History

#1 Updated by Antonio Falciano over 9 years ago

Hi Manuel,
an affine transformation in 2D is a roto-translation with scale variation or, alternatively, a polynomial transformation of the 1st order (n=1). So the minimum number of GCPs necessary to perform such transformation is: (n+1)(n+2)/2 = 3. When the GCPs are three, the RMSE should be always zero, because there aren't enough degrees of freedom in order to apply the least-squares method. Instead, if there are at least four GCPs, then the RMSE becomes significant and can be used in order to understand how well the transformation is performed.

#2 Updated by Manuel Madrid over 9 years ago

  • Status changed from New to Invalid

Hi Antonio,

You are totally right. Thank you so much for that wonderful explanation. I just closed the issue.

Best,
Manuel.

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