The effective sidelap of a Pix4D captura mission is much fewer than the input I put in the app

PIX4Dcapture PIX4Dcapture Questions/Troubleshooting
1

Hi,
My name is Sebastián Sánchez, I am R&D Engineer in EIWA Argentina. We recently started using Pix4D capture as our software for planning surveys, and also bought a license from you to use Pix4D Mapper.
While processing and evaluating the missions, we realized that the effective overlap we were obtaining was quite smaller that the one we introduced as a parameter in Pix4D capture.
So firstly, the main questions are:

  1. How do you calculate the overlap ? (Or since overlap is an input, how do you calculate the distance between shoots necessary?)

  2. What is the value between parentheses next to overlap ? (for instance, if I put 85% of overlap, in the app it appears : " 85% ( 77%) " . Is this the sidelap?

  3. Why is there a difference between the overlap we input to the app, and the effective overlap obtained in the photos?

  4. Pix4D Mapper user manual says that for agriculture surveys we should use images with 85% of overlap. Is this value the one we should obtain effectively in missions, or is this value the one we should put in the Pix4D Capture app ?? (since both values are quite different this is a very important issue that concerns us)

Our missions parameters where:
Vehicle: Phantom 4 Pro
Relative Altitude: 20 mts
Overlap desired (input of the app): 85%

Seeing the EXIF data of the photos, we obtained the position and orientations of the photos ( Lat, Lon, Alt, Roll, Pitch, Yaw). With them, we computed a mean distance between photos of 6~7 mts. With 20 mts of altitude, the footprint is of 20 x 30 mts (foward, sidewards respectively). With a distance between the position of the UAV of 6 or 7, we obtain an aproximated overlap of (20 - distance) / 20 = 65% for distance of 7 mts and 70% fot distance of 6 mts. This is quite far away from our desired value of 85%.

Also, we created some tools that projected each footprint on the ground, and computed the overlap for every pair of photos using this projected footprints, and we obtained in one mission an effective overlap of 69% and in another an effective overlap of 68%. These results are coherent with the results obtained with the technique I discussed in the previous paragraph.

I look forward to your reply, thank you!

Yours sincerely,

Sebastián

1 Like
2

Hi Eiwa,

Have you confirmed you are using the best resolution aspect ratio of 3x2?  16:9 and 4:3 are essentially cropping your sensor size.

Best wishes,

Aaron

3

Yes, of course!

We are using Android, with 3x2 ratio, and flying at 20 mts high.

4

Hi, 

we would like to inform you that the issue is fixed in the Pix4Dcapture version 4.2.1. 

More information in the technical release notes.

Best,

5

Hi Sebastian,

Did you get an answer to your question above? I mean, what is the value in the parentheses?
Thanks in anticipation.

Israel

6

Hi @israeltaiwo,

The value in parentheses next to the overlap percentage in PIX4Dcapture represents the actual overlap that is achieved based on the number of lines and the defined overlap value. This is an adjustment to ensure that the side distance between two images is close to the defined overlap value. So, if you set an overlap of 85%, the number in parentheses for example, 77% indicates the actual side overlap that will be achieved with the current mission planning parameters.

Cheers,
Daniele