We've been doing some route surveys in forested areas and are having a lot of problems with the photos registering. Any tips and tricks for improving these results? More overlap? Fly higher? Fly lower? Any suggestions are appreciated.
I should add that we do the majority of the processing in Pix4D.
I'd suggest you supplement with higher flights near your ceiling.?ÿ The greater distance between you and the tree tops, the easier time it's going to have matching the photos.
Lee D,
You left out a lot of variables.
A few questions:What are your side and front overlap?
- What is your AGL?
- How many flight lines are on your route?
- Are you using Terrain awareness?
- Are these trees conifers?
- Are the trees deciduous, what season? Are the leaves on?ÿor?ÿoff?
- Is your camera NADIR or oblique?
- Are you using mapping grade GPS w/ GCP's, how many?
- Are you using RTK or PPK?
- What drone, sensor, and camera?
- Are looking for just an ortho-mosaic, or trying to calc 3d and elevations?
Mapping a route with a drone, I find you need at least?ÿ4 flight lines. Mapping deciduous?ÿtreed areas are best down in the winter with only a few inches of snow cover. Pix4d will map through?ÿthe trees down the ground survey. Mapping through conifers is almost impossible. Creating just the ortho-mosaic at too low AGL, may create camera mis-matching, if you don't have PPK or RTK and a good sensor.
Oh...I would like to see how this pans out...I've had the same issues.?ÿ
Summer aerial from Google
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Winter aerial from Pix4d
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Proper?ÿaerial mapping requires paying close attention to lighting, shadows, environmental, and local features. Time of year, and time of day are important. In winter?ÿconditions with snow, you do NOT want to fly on bright sunny days, overcast is best. Unfortunately for me, around here, it is very cloudy all winter. In summer conditions you do NOT want to fly on cloudy overcast?ÿdays, sunny days near noon is best to reduce long shadows.
Can you fly on a day with zero wind?
I like the little point cloud that Pix4d produced as you can see the common points it uses to stitch the images together.?ÿ You can start to get an idea of what to look for.?ÿ We map (attempt to map) water all too often and it has very similar issues as the heavily vegetated areas.
Do you have the time to apply for a waiver to exceed the 400'??ÿ Are you near anything that matters with the altitude?
?ÿ We map (attempt to map) water all too often and it has very similar issues as the heavily vegetated areas.
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Mapping water is the easy bit - it tends to be level! Getting an ortho image of large expanses is the problem - lots of photoshopping.
Lee Green outlines all the salient points, although we would use 5 as a minimum number of lines along the route, or you might be zig-zagging cross route all the way. With a fixed wing you always fly cross wind so if we are crossing the route then we tend to get at least 7 images on each cross section. Drop off tends to occur only along the outer edges.
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The drone is a Microdrone MD4-1000 with a Sony ILCE-7R 32MP camera. The pilot is doing something else today and doesn't have the controller handy but he believes the parameters were 75% side and 80% forward overlap flown at 60m AGL. No RTK, PPK, or IMU, just trying to register using the EXIF data and then add in GCP. All of the flights have more than four lines, 4 of the six were flown perpendicular to the route and the other two covered larger areas than just the route itself. The trees (on this project area) appear to be mainly conifer and are foliated. No snow in South Louisiana lol.
This time of year you're always fighting weather conditions... lighting, wind, etc. I just want to ensure that we're collecting our data with parameters that give us the best chance for success. We had six flights totaling 1887 images and Pix4D threw out 281 of them, all in areas of heavy canopy.
With windy conditions, low AGL and long flight lines, the shadows may change enough that the overlapping images don't match anymore.
Fly higher, with low winds and use PPK. I'm sure that $64,000 drone is capable.
In Pix4D - Step 2, set the minimum number of matches to 6, the default is 3.
I have LiDAR. The client wants photogrammetry.
No, not capable of RTK/PPK with the photo package. Not $64K with the photo package either.
What is the issue, other than photos being rejected? Are you seeing flipped images or gaps in the ortho-mosaic??ÿ With that?ÿ 32MP camera you should good results at 220' or 240'.
There are some gaps and some distortions. I'll post a couple of screen snips tomorrow.
