Criss Cross Obliques With Less Overlap Versus One Direction?


#1

I’m doing a topographic survey of a rural area with about 500ft of elevation change (I’m breaking it up into sections where each section has only 250ft of elevation change). Will output a DXF with contour lines and possibly a DEM or DTM. I only need accuracy within 12 inches. Will have ground control points.

Obviously when you are generating output for 3D features, it’s more accurate to also have obliques. One can see the crispness of the structures and lack of blobbing/noise that the use of obliques contributes.

Given the accuracy requirements and that this is mainly for land features, not structures, I am wondering the following:

(a) In general you want 1/3 GSD so 4in/pixel for 12-inch accuracy, that’s low, I will be twice better GSD. And I’ll have 80/70 overlap which is also pretty decent. In that case, are obliques in reality a waste of time?

(b) If I did do obliques, what would produce better results, run a mission in one direction with 80/70 frontlap/sidelap, or run two missions in two different directions (criss cross) but with 50/40 overlap/sidelap. In other words is having more overlap in one perspective more valuable than having two different perspective obliques with less overlap? Again this is for land topography measurement, not 3D modeling of structures.


#2

Hello Jeff,

Thanks for reaching out. Running one mission with an overlap of 80/70 should suffice vs running two missions. I would even push your overlap to 80/80 for more accurate results. With oblique imagery, this will help define your 3D model and produce a cleaner model. It all depends if you want this extra data. You will not need to provide a different perspective as our algorithm does well with a single perspective + high overlap. @consultant

Thanks!
Yusuf


#3

You might use the POI feature in the DJI GO app to get your obliques. Sequentially overlapped side facing or circular obliques give the best results compared to forward facing obliques.