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Author Topic: How to lower keypoint threshold limit  (Read 2992 times)

vik748

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How to lower keypoint threshold limit
« on: August 07, 2020, 02:18:42 PM »
Hi,
I am working with a set of images of ice which are low contrast and low texture.  When I use default settings of 40,000 keypoints, Metashape seems to only be able to detect a few thousand.
Is there a way to lower the keypoint detection threshold so that I can get more keypoints?  Possibly by adding something under Tools -> Preferences -> Advanced -> Tweaks

Thanks in advance.


vik748

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Re: How to lower keypoint threshold limit
« Reply #1 on: August 07, 2020, 04:55:11 PM »
Here is an example of the keypoints detected, see attachment.

Alexey Pasumansky

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Re: How to lower keypoint threshold limit
« Reply #2 on: August 08, 2020, 02:22:04 PM »
Hello vik748,

Which Accuracy setting do you use and what is the Tie point limit?

Also please specify the image dimensions.
Best regards,
Alexey Pasumansky,
Agisoft LLC

vik748

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Re: How to lower keypoint threshold limit
« Reply #3 on: August 08, 2020, 03:09:45 PM »
Alexey,
The settings are:
Accuracy: Highest
Key point limit: 60,000
Tie point limit: 100,000

This particular image is from a drone and is 5472 x 3078.  I also use similar images from go pro camera which are 4000x3000.

Alexey Pasumansky

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Re: How to lower keypoint threshold limit
« Reply #4 on: August 08, 2020, 03:23:29 PM »
Hello vik748,

Then the images may be just too noisy (or do not have sufficient overlap), if there are too few tie points detected even with Highest accuracy.

Note that tie point limit value higher than key point limit would not have any effect - it is equal to tie point limit = key point limit (or just tie point limit set to zero value).
Best regards,
Alexey Pasumansky,
Agisoft LLC

vik748

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Re: How to lower keypoint threshold limit
« Reply #5 on: August 08, 2020, 03:31:18 PM »
Alexey,
I am only thinking about the detected keypoints and not tie points at this time. The white points are all the detected key points and as you can see they are way less than 60K.
Most feature detectors like ORB and SIFT allow you to choose a minimum threshold to be called a keypoint. Is there any way I can try to reduce that kind of threshold below the default values in Metashape.
Since I am looking at ice, my images are always like this and can't do much while capturing them.
Thanks,
Vik

Alexey Pasumansky

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Re: How to lower keypoint threshold limit
« Reply #6 on: August 08, 2020, 03:41:52 PM »
Hello Vik,

Key points are not shown in the Photo view mode. You only see tie points (blue - valid, i.e. used tie points, and white - invalid, i.e. unused).

The number of detected key points per image is shown in the processing log (in the Console pane) during the matching operation.
Best regards,
Alexey Pasumansky,
Agisoft LLC

vik748

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Re: How to lower keypoint threshold limit
« Reply #7 on: August 08, 2020, 05:05:26 PM »
Alexey,
Thanks for that information.  I stand corrected, from the logs I see that Metashape is indeed detecting the required number of points. 

Are there any other tips / tweaks that could be used to improve the matching process?  I have uploaded a few test images to https://drive.google.com/file/d/1O6ib_RFUzzZssZxQyrINJEE5gMDDVkgl/view?usp=sharing

As you can see from the images, visually we can easily track between the images, however Metashape is not able to match the keypoints well.  Are there any settings / tweaks that could help Metashape with the matching?

Thanks for all the help,
Vik