Sub 0.33 cm GSD Mapping

[Adam_16180]

Hello, I am attempting to do some very high resolution mapping that's needed for a weed mapping project in a very flat field. I have the Mavic 3E however when attempting to set the GSD to lower than 0.33cm it wont let me as the min altitude is39ft for mapping projects for some reason? Is there a way to change this so that I can map from a lower altitude?

 

[Yogi053]

033cm? Is that correct? (1/8 inch)?

 

[FletcherAero]

did you try slowing the speed down?

 

[Adam_16180]

@Yogi053 thats correct 1/8" the weeds are very small 1/16th would be perfect so I can differentiate the species of weed, any idea if I can lower the mapping altitude to lower than 39'? Im not sure why thats the minumum. I think @FletcherAero you're suggestion is also good I should try slowing it down as its a rolling shutter so it should help. Plus I had the camera on Auto setting and its winter in Canada so not alot of sunlight. Any reccomnedations on the speed/ camera settings would be really helpful! Thanks for the inputs guys.

 

[jaja6009]

With such a low GSD and associated images, mapping something that is possibly too homogeneous, you may run into problems getting the images to align. If the software does align them, you may run into the issue of bad/false alignment and depending on the software have issues. Pix4D may form multiple blocks and something like agisoft will have multiple planes showing the ground.

The software is attempting to save you from having images that will have trouble aligning by limiting you altitude.

If you are using the Mavic 3 Enterprise, it has a mechanical shutter and can map at much higher speeds than other cameras without it.

Flying so low with the required frontal overlap will have the drone snapping images at an extremely fast rate, possibly going past the ability to take the image, and save it before the next image needs to be taken.

Is this project for a large area? If so that will be your next problem since you will have to fly slower.

As far as camera settings:
Shutter Priority
ISO 100 to 200
Shutter Speed set according to the lighting. Faster if sunny, slower if cloudy.
Selct Sunny or Cloudy according to conditions.
Monitor your aperture. You want 4000 to 5000. to get there you may have to adjust EV in small increments and make sure when you adjust the EV you are seeing this setting on the grass/field when you adjust.
Set Focus to infinity after you get to your operating altitude and autofocus.


You truly may want to use a better system for this. A better camera would allow for lower GSD at a higher altitude, but at the end of the day, your required GSD may prove to be a problem.

Also RTK module receiving corrections should help with your alignment.

 

[AMann]

That’s really high resolution. Pole photography using a good camera and fixed lens (like a DSLR) would be good also, especially in low light if the field isn’t too big. Use little markers as GCP’s and a good amount of overlap on each photo.

 

[Meta4]

thats correct 1/8" the weeds are very small 1/16th would be perfect so I can differentiate the species of weed,

needle <==> haystack
It sounds like you might be hoping for more than what's possible.
Find some larger weeds to work with.

 

[jaja6009]

Try fooling it by changing your takeoff altitude in the one setting, Target Surface to Takeoff Point.

This will totally screw up the GSD calculation though.

This does sound like a cool project, maybe someone else will chime in with a solution.

Maybe try this by shooting 4K video. Pix4D and Agisoft have workflows for using video in photogrammetry. Just keep in mind that 4K video frames work out around 8MP images but being low will help. But there will probably still be alginment issues.

In the end, run some tests and let us know the results, you definitely have my interest!