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OpenDroneMap / ODM

A command line toolkit to generate maps, point clouds, 3D models and DEMs from drone, balloon or kite images. 📷
https://opendronemap.org
GNU Affero General Public License v3.0
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Offsets for GCPs - how are they calculated and why #713

Closed CarlosGrohmann closed 6 years ago

CarlosGrohmann commented 6 years ago

Checking the log for a dataset processed with ODM using GCPs, I noticed this (only 4 first lines of GCPS shown):

Reading following GCPs from file:
x_: 316675 y_: 7.40503e+06 z_: 939.968 pixelX_: 638 pixelY_: 2970 image: DJI_0026.jpg
x_: 316689 y_: 7.40508e+06 z_: 918.39 pixelX_: 726 pixelY_: 172 image: DJI_0026.jpg
x_: 316689 y_: 7.40508e+06 z_: 918.39 pixelX_: 472 pixelY_: 578 image: DJI_0027.jpg
x_: 316689 y_: 7.40508e+06 z_: 918.39 pixelX_: 208 pixelY_: 1131 image: DJI_0028.jpg

The calculated easting offset for the georeferenced system: 316587
The calculated northing offset for the georeferenced system: 7.40506e+06

Recalculated GCPs with offset:
x_: 88.449 y_: -23.201 z_: 939.968
x_: 102.126 y_: 27.739 z_: 918.39
x_: 102.126 y_: 27.739 z_: 918.39
x_: 102.126 y_: 27.739 z_: 918.39

This is similar to the optional 'shift' of coordinates in Photoscan. From what I could find, this is done to increase the numerical stability of the computations.

Thinking in a proper description of methods (for a near-future scientific paper), I wonder if someone could provide a simple explanation about the 'numerical stability', or point me to a reference.

thanks

dakotabenjamin commented 6 years ago

This issue was moved to http://community.opendronemap.org/t/offsets-for-gcps-how-are-they-calculated-and-why/360