Pix4D Mapper Checkpoints vs Densified Points

Pix4D International
1

Hi everyone.
i would like to know if someone already has encounter this problem or situation regarding checkpoints and densified points on the densified point cloud.

My block is already adjusted to my 3D GCPs, the QR says it has a RMS error of 0.003 m which is pretty good.

Now here’s the problem.

i have already added several checkpoints in the project. i Reoptemized the project in order to check the consistency of the added checkpoints. the QR tells me that i have a 0.001- 0.006 error on the different checkpoints around the project which is actually pretty good, but here’s the strange part, when i zoom in to checkpoints, they seem rather far from the densified points on the point cloud, for example, one of the checkpoints is almost 25 centimiters long from the closest Densified point meanwhile the QR says that is has a 0.006 m error from the computed coordinated.

from what i’ve read and seen, we need to trust the statistics that the QR shows regarding the accuracy of the checkpoints added, but does someone know what does the actual distance between the computed and the densified point mean?

checkpoint.tif (424.6 KB)

QR.tif (68.9 KB)

2

Hello Jose,

Welcome to the community!

The distance between the computed and the densified points can vary depending on the reliability of the information it is given. In this case, you might want to look at the marking of the Ground Control Points(GCPs) and Check Points(CPs) as any amount of error there can be transferred into the computed value. You might also want to take one or two of your CPs and make them GCPs as I see 3 GCPs and 5CPs in your quality report. GCPs are included in the computed equation and can improve the accuracy found at the CPs.

I hope you find this info helpful. Should you require further assistance it is best to send the full Quality report along with the log and .p4d files.

I’m attaching a few documentation articles you might find helpful as well:

Tie points in photogrammetry project (ATP, GCP, MTP, and CP)

How are tie points errors defined - Mean, Sigma, RMS?

Step 1. Before Starting a Project > 4. Getting GCPs on the field or through other sources (optional but recommended)

Best Regards,

-Jon