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Topics - Eichhorn18

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General / Import marker coordinates for coded reference markers
« on: November 22, 2019, 12:56:09 PM »

I am trying to find out how I can assign local coordinates which are known (measured manually) to a set of coded 12-bit circular markers that metashape generates. My workflow is this:

1. Generate 12-bit coded circular markers in Metashape.
2. Print the markers, and attach to close-range photogrammetry model.
3. Measure the location of the coded-markers in the physical model.
4. Photograph model.
5. Align images.
6. Detect coded-markers.
7. Import marker locations (X, Y, Z). These were entered manually into Metashape in a previous model, however the coordinates remain the same and so to avoid re-typing them into the coded-markers, I import these from an XML markers file.

The issue is that when I import the markers, then appear as seperate markers from the identified coded targets. My question is how can I detect the coded markers (numbering 1 to 30), and then import the coordinates and assign them to those coded targets without the need to type in the coordinates?



I am processing image data from a very flat surface that has been textured visually to allow good tie point recognition. After processing the point cloud in Metashape, I am exporting the pointcloud to a data analysis program to generate contour plots of the flat surface. I have noticed some sort of noise, or rounding error being generated in Metashape. The parameters I am using to generate the sparse and dense point cloud area below:

number of photos: 35
Align photo accuracy: Highest
Generic preselection: ON
Key point limit: 40000
Tie point linit: 0

The model was then filtered by reprojection error to remove points with error above 0.2. After each gradual filtering and removal, the camera calibration was optimized for f, cx, cy, k1, k2, k3, p1 and p2. Several rounds of the gradual selection were necessary. The sparse point cloud had 12,572 points after filtering.

To generate the dense cloud:
Quality: Medium
Depth filtering: Disabled
Calculate point colours: ON

After this step, I create some markers in a local coordinate system. The markers are placed on the checkerboard grid below the object and z = 0 is at the level of the checkerboard. The textured surface physically sits about 15 mm above the checkerboard. The markers are added and turned on and then the refresh button is pressed in the references tab. My understanding is that this updates all the coordinates of the point cloud. The cloud is then exported as a .PTS file.

I then do some analysis of the data to grid the information at regular X Y spacing and return a Z value of the point cloud. This is essentially fitting surface by triangulation through the point cloud and then extracting the height value at regular X Y intervals. The data is then contoured, and the noise I am seeing is appearing in this contoured data as well (contoured_data.jpg).

The process of gridding the data and contouring it is not producing the sawtooth pattern in my opinion as the patterning is visible in the raw point cloud when you view this externally from Metashape, with no manipulation of the data. Simply viewing the 3D point cloud with no point colours (processing_01.jpg) shows this pattern or a very similar pattern.

Has anyone encountered this kind of noise / sawtooth pattern when generating point clouds for very flat surfaces?


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