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?
Sub 0.33 cm GSD Mapping
- Thread starter Adam_16180
- Start date
FletcherAero
Well-Known Member
@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.
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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.
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
Well-Known Member
needle <==> haystack
It sounds like you might be hoping for more than what's possible.
Find some larger weeds to work with.
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!
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!
AMann
Well-Known Member
By pole photography I’m talking about an A-frame setup. We used something like that to map out kangaroo rat burrows over a 3-year period in a study area before good GPS was available to the general public back in the ‘80’s by using a Nikon F (film camera!), a fiberglass measuring tape and two retractable painter’s poles.
The mount consisted of a board with two oval shaped holes in it that we stuck each of the two pole tops through. The poles were connected together at the top. The board holes were at a distance that made it possible to stretch the bottoms of the polls out and keep it steady at the top, and the camera was mounted on the bottom of the board with a L-bracket that was attached to the bottom of the board. The board was also tethered to the top of the poles to keep it from sliding down the poles when we closed up the A-frame. We had a long electronic release cable for the shutter, but with today’s digital technology, you can do it with the IR remote controller on a DSLR.
It takes two people to do this- one at each leg of the A frame with the camera mounted downwards at the top. We used a measuring tape tied between the bottoms of each leg to provide an image scale but also to allow us to keep the leg bottoms stretched out the same distance so the camera height was always the same as well. The imagery was superb and you could easily resolve small forbs with it.
If you use a small digital camera with good resolution, you could also do this with a single long pole held out an an angle over the ground as well. Use a string and plumb bob attached near the camera and long enough that it touches the ground at your desired height so you can center it and keep it at a standard ground distance for each shot. My wife’s archaeology company uses one like that to get 3D images of boulders and rock outcrops with milling slicks and bedrock mortars on them. I use my drone every once in a while for them when the rock outcrop is too big to do it just with the handheld pole. But even with the drone flying as low as I can get it manually, I don’t think it’s getting the type of ground sampling distance resolution you were thinking of.
The mount consisted of a board with two oval shaped holes in it that we stuck each of the two pole tops through. The poles were connected together at the top. The board holes were at a distance that made it possible to stretch the bottoms of the polls out and keep it steady at the top, and the camera was mounted on the bottom of the board with a L-bracket that was attached to the bottom of the board. The board was also tethered to the top of the poles to keep it from sliding down the poles when we closed up the A-frame. We had a long electronic release cable for the shutter, but with today’s digital technology, you can do it with the IR remote controller on a DSLR.
It takes two people to do this- one at each leg of the A frame with the camera mounted downwards at the top. We used a measuring tape tied between the bottoms of each leg to provide an image scale but also to allow us to keep the leg bottoms stretched out the same distance so the camera height was always the same as well. The imagery was superb and you could easily resolve small forbs with it.
If you use a small digital camera with good resolution, you could also do this with a single long pole held out an an angle over the ground as well. Use a string and plumb bob attached near the camera and long enough that it touches the ground at your desired height so you can center it and keep it at a standard ground distance for each shot. My wife’s archaeology company uses one like that to get 3D images of boulders and rock outcrops with milling slicks and bedrock mortars on them. I use my drone every once in a while for them when the rock outcrop is too big to do it just with the handheld pole. But even with the drone flying as low as I can get it manually, I don’t think it’s getting the type of ground sampling distance resolution you were thinking of.
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