Phantom 4 camera + dronedeploy + metashape : tie point holes

[Dukytony]

Hello Everyone,

Currently working on a big mapping project.

tiles are 500x500 m of sand and rocky deserts.

Gear :

Phantom 4 camera
Dronedeploy
Metashape

Dronedeploy was set in automatic settings :

75% front overlap
65% side overlap
pictures are taken with F/2.8, ISO 100 and 1/4000 shutter
fly altitude : 45 m
flight speed : 5m/S

I have pretty big holes in my tie points resulting in some errors in the orthomosaic. I think is probably linked to the sandy nature of the ground. There is not a lot of colour variations so after pictures alignement i often have bunches of pictures that metashape was'nt able to align.


So according to you guys, what parameter should I modify to get a better tie point?
increasing the overlap?
lower flight altitude?
slower flight speed?
changing camera settings?

I want to be able to do one tile using 3 to 4 batteries so i won't be able to modify all parameters. So wich one would be more effective on the results?

Thanks a lot!

[seitse]

Hello

I have the same setup.

The altitude i use is around 60 to 70m and the side overlap 70%

Other than that i use the auto settings from dronedeploy.

[GGR]

Hey Dukytony,

In my opinion, gaps in your attachment points are not a real problem. If all of your cameras are aligned and the overall accuracy meets your needs, the next steps will "close" those gaps. As for your flight parameters, a few meters higher could help increase your forward and sideways overlap from 75/65 to 80/70 without using more battery. This should help you avoid alignment issues while maintaining high resolution.

Cheers

[Dukytony]

The problem is I can't really fly higher because I need a 2cm/pix minimum resolution.

Here are the kind of orthomosaic errors i have. I assume this is due to these holes in tie points?

So wich flight parameter should I change?

Thanks a lot!

[dpitman]

For any homogeneous surface topography, you probably want to use 80/80 overlaps at a minimum.

[GGR]

Assuming you are planning a single ortho fly (pitch and roll to 0°), in my opinion the two options you have would be to plan an oblique survey in addition to the ortho or increase the overlap setting. Both of these options will make you use more battery anyway.
Could you also share your workflow's settings?

[Dukytony]

Workflow settings :

alignment parameters
accuracy high
generic preselection yes
reference preslection source
key point limit 40000
tie point limit 4000
exclusde stationnary tie points yes
guided image matching no
adapative camera model fitting yes

depth maps generation parameters
quality medium
filtering mild

mesh
reconstruction parameters
surface type arbitrary
source data depth maps
interpolation enabled
strict volumetric masks no

orthomosaic

reconstruction parameters
blending mode mosaic
surface mesh
enable hole filling yes
enable ghosting filter no


I have to add that no all of the tiles have errors like this. it's mostly the tiles where there is not a lot of colour variations (only sandy ground with fewers rocks)

Thanks a lot for your help!