"Error" reported by PS: what is this?

[dowallin]

I am following the v1.2 tutorial with GCP instructions. I've also run the Lens program to obtain camera calibration parameters.

PS reports an "Error (m)" for both my cameras and for my markers (GCPs). I'm trying to understand what these values represent and how PS calculates these values.


My GCPs were obtained using a very nice Trimble GPS and, after post-processing, the Trimble software reports and error for these GCPS in the range of 5-15 cm. So I feel pretty good about the accuracy of these locations.

Imagery comes from a camera flown on a small quadcopter. My camera locations are based on instantaneous GPS positions logged for each photo using the internal GPS in my Canon S100 camera. So I realize that these locations have a fair amount of error; probably 10 m or more.

[Alexey Pasumansky]

Hello dowallin,

Probably the page 46 in PhotoScan Pro manual (http://www.agisoft.com/pdf/photoscan-pro_1_2_en.pdf) will be helpful:

What do the errors in the Reference pane mean?
Cameras section
1. Error (m) - distance between the input (source) and estimated positions of the camera.
2. Error (deg) - root mean square error calculated over all three orientation angles.
3. Error (pix) - root mean square reprojection error calculated over all feature points detected on the
photo.

Reprojection error is the distance between the point on the image where a reconstructed 3D point can be
projected and the original projection of that 3D point detected on the photo and used as a basis for the
3D point reconstruction procedure.

Markers section
1. Error (m) - distance between the input (source) and estimated positions of the marker.
2. Error (pix) - root mean square reprojection error for the marker calculated over all photos where
marker is visible.

Also note that it is recommended to optimize the camera alignment after placing markers (cameras can be unchecked in the Reference pane, as the GCPs are measured with the considerably greater precision).

[dowallin]

Alexey,
Thanks for your reply.

But I'm still a bit confused. What is the "input (source)" from which these error measurements are derived?

D

[Alexey Pasumansky]

Hello dowallin,

Source values are those that are loaded to the Reference pane from the external ext file of extracted from the image EXIF. Actually on your screenshot the Source values tab is displayed.