Bendy Data! Help!

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

Hi everyone, looking for some help with a point cloud I’m processing. I have a wall I’m looking at, 175m long approximately, which I have photographed sequentially moving left to right, manually. The overlap is around 40% or 60%, and the images are 20MP and very nicely focused. I also have a video of the wall, which is filmed in 4K at 48fps, and therefore I can lift frames.

No matter what I try, combinations video, stills, lots or not many images, I end up with a bend in the wall (Which ought to be flat & straight - ie horizontal)

I’m wanting to put these XYZ’s into cloud compare to merge them with other data, however this bend is making it impossible. There is no need to create DSMs or Orthos from this.

I would prefer not to have to create MTPs, as I feel this ought to be doable without that effort (which might or might not yield good results). There were GCPs in the survey but they are not visible in this section.

Would appreciate any pointers you can give to assist. Time is of the essence… and this is the last part of the project!

NB: three other walls worked nicely, albeit they had some more depth and 3D structure to work with.

Using the Alternative method in the initial processing straightens out the wall in the vertical plane, it still droops at one end.

Furthermore, I can’t seem to meld the two image sets together, ie video frames and geolocated stills when using the alternative tie point method. What is the ratio? I can then be selective and remove video frames that duplicate what the geo stills see…

2

60% overlap would be the bare minimum to get a project to process with photogrammetry. I have found that I need 85-90% overlap for handheld pictures, especially if you are only taking one row of pictures. I try to have one pixel visible in 8-12 pictures. Easier done when you are taking many rows of pictures. 

If I was capturing a wall, I would have a minimum of 3 rows captured. One as high as I can get the camera, One in the middle and one as low as I can. All pictures would shot with a very wide lens, making sure to capture the entire height of wall in every picture taken. Remember, we are trying to see the same object in every photo from  many angles. I you cannot see the entire height of wall in every picture, turn your camera sideways, but this will require even smaller left/right movements to get the 85-90% overlap.

3

Hi Amy,

as Tommy correctly pointed out, you might not be able to well reconstruct your model because of insufficient overlap. We recommend having at least 85% overlap for features such as single track corridors or walls. 

Which type of camera are you using? Does it have a rolling shutter? The speed and the distance to the object might also be the cause of your troubles. 

If you can’t obtain better results increasing the overlap, please send us the quality report of your project so that we can better help you.

Cheers,

Alice