Is scale constraint mandatory?

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

Hi!

I have made photogrammetric models with a Mavic 3E drone without GCPs. Before taking photos, I have taken manual measurements from the area. When I have checked these measurements from point cloud in pix4d mapper, I have found that the differences in relative accuracy are usually about 0.5%, or even less.

This is usually completely sufficient accuracy for my needs, so my question is:

Do I need to create a scale constraint in the point cloud or is checking the manual measurement(s) from the point cloud enough to verify the relative accuracy, as the point cloud is automatically scaled, when the pictures have GPS information?

If the manual measurements are measured from the point cloud and they are accurate enough (max 0.5% error), does the scale constraint provide any additional value for my point clouds relative accuracy?

And I’m only interrested about the relative accuracy not absolute accuracy.

Best regards

Sami

2

Does anyone have any perspective or opinion on this matter?

3

Hi samik,
I’m a Pix4D User; when I need to certify/assure that I’m providing good results, even if I don’t have GCPs, I just check the manual measurements (I like to put one of These on the ground as a 1mx1m “L”) vs the Pix4DCloud results, and I write a report on the accuracy: both Pix4DCloud and Pix4DMapper have very good capabilities of Auto-detect Keypoints, so the Scale Constraint is just optional.
However, if I notice more than 3% Measurement Error (or more than 5% Calibration Process error), I redo the project in Pix4DMapper, using the Manual Measurements as Scale Constraints.

Regards,
Giancarlo

4

Thanks you for your aswer and information about your way of working. It sounds good.

I do almost the same thing. Check the point cloud and the orthomosaic visually, check the manual measurements and Quality Report and if everything is good, I write a document about the relative accuracy etc.

Best Regards

Sami