I agree with @Saijin_Naib - altitude isn’t really a factor for ODM, but good coverage of your subject surface is. I fly a lot of vertical faces (manually), and the altitude on those is all over the place.
Within certain tolerances, varying flight height can actually be helpful, especially for 3D and elevation modeling. You can think of it as a sampling problem: by sampling different heights, you get better sampling information about height, and improve your model.
Typically, we fly at a single height either a single height above ground surface or the flight origin for a couple of reasons. For the rest of the paragraph, I will be guessing at what DroneDeploy and MapsMadeEasy or trying to accomplish with their recommendations. Flying a single height above the origin, if we have some variation in terrain heights and trees and buildings etc, gives us some of that variation in effective height that helps us get better 3D and elevation data. It doesn’t work well in very flat areas to do this, but is good in many circumstances, and is simple to flight plan. Flying at a single height above ground gives us even sampling across our study area, and ensures that, for ground pixels anyway, we have a know sampling resolution and optimizes for better XY sampling.
DroneDeploy and MapsMadeEasy are platforms that are trying to optimize the quality of the outputs of the datasets processed through their platforms in different ways, but the reality is, you can decide your own requirements, and fly accordingly. That said, I almost always vary height or height and camera angle, because correcting for distortion in Z aids a lot the overall quality of any imagery collected.
I came up with this idea, If i were to map let’s say 10 acres, i would first fly at drone deploys standardized 200 feet and then do an additional run at a lower or higher altitude depending on the complexity and the topology of the area so i get more samples of angles and heights which would ultimately lead to a better model.
I feel like having a two layer model for medium to small mapping plots can help create a better model than having one at a standard height.
i also want to add that while mapping around objects like sheds, ditches, singular houses, irrigation ponds, canals etc which has a sharp rise/fall in height, the more samples we have the better.
Ive often seen this issue while bench marking where structures such as houses etc kinda don’t have the shape they are supposed to have, when i press the show camera button to analyze where the images were taken i see that the number of images captured thought the land was oblivious to the details. a place with lots of details got the same number of images clicked just like a place with little to no detail to capture.
I feel like it beats the point of aerial mapping if we don’t pay attention to details.
I have a drone, spent a few years doing agricultural field survey and am a GIS professional, and I learned a TON from Steven’s writings. I only wish I had found them back when I was still doing field survey.
I need to write new posts: I have new recommendations. These recommendations aren’t bad, but they are expensive from a flying time perspective. I’ve got some slightly modified ones that will still give good results, but reduce that field time when needed.