Interpreting intersection error colormap

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christina Toldbo

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Sep 1, 2022, 12:03:11 PM9/1/22
to Ames Stereo Pipeline Support
Hello

I am working on getting a grip on how different inputs affect the output DEM for Dawn images and I am looking at choosing optimal pairs. I would like to use the triangulation error as an indirect measure of quality but I am wondering how to interpret my intersectionerror map.

In the documentation it says: 'A DEM with high triangulation error is always bad and should have its images bundle-adjusted. A DEM with low triangulation error is at least self-consistent but could still be bad.'

But what is a high and what is a low triangulation error?
It also says 'This error in the triangulation is the shortest distance between two rays' is that in pixels or how is this distance defined?

Thank you so much,
Christina

Alexandrov, Oleg (ARC-TI)[KBR Wyle Services, LLC]

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Sep 1, 2022, 12:19:35 PM9/1/22
to christina Toldbo, Ames Stereo Pipeline Support
A good criterion for selecting stereo pairs is the convence angle. There's more details here: https://stereopipeline.readthedocs.io/en/latest/examples.html#guidelines-for-selecting-stereo-pairs.

I added to the doc that triangulation error is measured in meters (those are physical rays, emanating from the cameras and going towards the ground). I also clarified that error should be compared to ground sample distance. So, if your image resolution is say 5 m/pixel, if the closest the rays get to each other is 10 meters, that is likely quite bad. 





 

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Subject: [EXTERNAL] Interpreting intersection error colormap
 
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christina Toldbo

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Sep 1, 2022, 2:09:14 PM9/1/22
to Ames Stereo Pipeline Support
Thank you very much for the clarification. It is very helpful!

Is there a way to analyse the values of the intersectionerror map? So far I have converted to a colormap but is it possible to show a colorbar or another indication of the actual values? My ground resolution is 60 m/pix so I also ran colormap --min -60 --max 60 and I get this attached map. Should that be interpreted as that the errors are less than +/- 60 (since the colors are not dark?)
-IntersectionErr_CMAP.tif

Alexandrov, Oleg (ARC-TI)[KBR Wyle Services, LLC]

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Sep 1, 2022, 2:27:40 PM9/1/22
to christina Toldbo, Ames Stereo Pipeline Support
You should use for the colormap the min value as 0, as the intersection errors are positive. This tool is very simple and offers no colorbar. Normally the very bright shade of red is your maximum value. You can try colormap --min 0 --max 20, and see if the brightest value of red is reached.


Sent: Thursday, September 1, 2022 11:09 AM

To: Ames Stereo Pipeline Support <ames-stereo-pi...@googlegroups.com>
Subject: Re: [EXTERNAL] Interpreting intersection error colormap
 

Oleg Alexandrov

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Dec 1, 2022, 4:41:35 PM12/1/22
to Ames Stereo Pipeline Support
To add some completeness to this thread, stereo_gui can now colorize images and show a colorbar (https://stereopipeline.readthedocs.io/en/latest/tools/stereo_gui.html#displaying-colorized-images-with-a-colorbar-and-axes). (Also can do color scatterplots.)

This feature uses a different paining approach, based on Qwt, and is not yet integrated with other stereo_gui features (such as overlaying of images, zooming all images to same region, hillshade, overlay of scattered points), that will come later. For now this is in the dev build (accessible from the GitHub release page, and as usual, installable without admin rights)., 

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