I have a client who intends on doing a watershed analysis of app. 800 ha. Usually clients say they want the surface as accurate as possible but don’t really understand how GSD and it’s associated relative accuracy translates to the general accuracy of a site and how quickly the amount of data increases. i.e. if I say we fly at an elevation giving a GSD of 2 cm giving an relative /.absolute accuracy of 2-6cm in Z at each pixel they say its not accurate enough because they think the entire survey is off with that amount (It could be, if I don’t understand correctly either). Which when you compare to a GNSS survey where say every 20-30 metres a spot shot is taken with a precision of 2cm at best the interpolation across the surface is surely more prone too inaccuracies across the site when averaged. We will be using a fair amount of GCPs for the transformation to our local projection and checking as well as PPK and RTK to have redundant control.
So I’m not sure the accuracy actually required for a watershed analysis ( First time for this specific request, and the area only has a gentle slope to one side) where they require 25cm interval contours for planning a solar farm. I usually try to get my GSD between 1-1.2cm for any reasonable size site but in this case it amounts to crazy amounts of images. We use a M300 RTK and the P1 so the gigapixels for this project will be absurd. Also, regarding the overlap is it safe to assume we can use 80 even 75 or 70 front and 60 side lap due to the quality of the camera sensor being full frame and size of the image footprint because we can fly higher as opposed to a phantom 4 we have used in the past where you usually require 80 and at least 65-70 to get good matches when trying to get a GSD close to 1cm flying extremely low. I’m trying to find a balance between GSD and overlap, preferably reducing overlap as much as possible and pushing the GSD as high as possible without risk of creating a model which cannot even be best fit to the local control after processing.
Any advice will be appreciated as I can try process 15k + images ( we have a decent workstation) and survey the site in 2-3 days (We have a lot of batteries) but is it necessary as the data handling and presentation to the client will be so much more challenging especially on their side.
A suitable setup for parameters I think should be sufficient is a GSD of 1.5cm and Front lap of 75, side lap of 60. This equates to app. 9000 images.
Thanks in advance.