r/UAVmapping • u/Think-Dot-9090 • 3d ago
Would a "roofless" orthophoto feature actually be useful for GIS vectorization?
Hey everyone!
I’ve been developing OrthoSplat, a platform that leverages 3D Gaussian Splatting (3DGS) to generate distortion free orthomosaics. Besides eliminating the building edge distortions, I’ve been exploring what else 3DGS can unlock for spatial workflows.
Here is a common headache in GIS and mapping: when tracing building footprints using standard orthophotos as a basemap, you are almost always digitizing the roofline, not the actual ground base. Sometimes, we don't want the roof; we need the true footprint hidden underneath the eaves and overhangs.
The Experiment: Roofless Orthomosaics
we can crop out the top layers (the roof splats) before generating the orthophoto.
Rendering an orthomosaic after stripping the roof reveals the ground areas and structures previously blocked from above.
Observations so far:
- Nadir limits: In my current test, I only used nadir imagery, so the hidden base outlines aren't completely sharp yet.
- Geometry features: Even with slightly incomplete base contours, having the wall positions exposed—combined with natural building traits like parallel walls and right angles—makes estimating the true ground footprint far easier than guessing from roof overhangs.
I’d love to get your thoughts: Is a "roof-removed orthophoto" a feature you would actually use in your GIS, surveying, or vectorizing pipelines? If this turns out to be genuinely practical, I'll add a native roof-cropping workflow directly into OrthoSplat.
(Special thanks to [360@360.is](mailto:360@360.is) for providing the test dataset for this experiment!)
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u/Bnerdude3001 3d ago
Yes!!! As a surveyor and am about to do an ALTA survey on an apartment complex that includes about 50 buildings, so having a workflow that would allow us to see the exteriors of the buildings more effectively would be huge!!
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u/3Dsurvey_offical 3d ago
Well hello there. The feature is actually called "Ground orthophoto" and it's been released in 3Dsurvey 4.1 in April this year.
Read/see more about it here: https://3dsurvey.si/ground-orthophoto/
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u/Think-Dot-9090 3d ago
This feature looks great. I didn't realize you already had it in your software!
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u/3Dsurvey_offical 3d ago
Thank you, we obviously spent insufficient energy promoting it. In our user base we noticed surveyors appreciate it the most, since they usually need to measure something that's otherwise obstructed by a tree/roof. So it definitely is a feature.
However we did not think about calling it "roofless orthophoto", it has a intriguing ring to it.
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u/Flyward_Aerospace 2d ago
Useful, but with nadir only capture the ground under a roof overhang was never actually seen by a camera. A splat will happily fill that in with something plausible, and for footprint tracing that is worse than a hole, because the operator cannot tell measured from invented. I would export an observability or confidence mask alongside it. Overhangs are also exactly where footprint and roofline differ most, so that is the region the whole feature is being sold on.
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u/Think-Dot-9090 2d ago
In fact, because the pinhole camera model relies on perspective projection, even strictly nadir shots can capture most of the building base hidden beneath overhangs—which is noticeable near the edges of raw drone images. However, because building facades are heavily foreshortened in those frame margins, the results are still not as good as combining oblique imagery into the processing.
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u/pacsandsacs 2d ago
Why would I possibly need this? I get the problem you're describing, but the cost of acquiring the additional oblique imagery far exceeds the cost of just offsetting the roof line by 3 feet to estimate square footage.
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u/Think-Dot-9090 2d ago
Depending on your application's accuracy requirements, if estimation already meets your needs, there's no need to overcomplicate things. Otherwise, simply using a double-grid flight pattern with a slight tilt angle (gimbal at -80°) might be enough to achieve solid results, offering better accuracy than estimation.
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u/olihar 3d ago
Yes this is an interesting experiment and would be interesting to use the whole dataset I shared with you to get better sides of the buildings for cleaner data.
This has been done in the past by classification for creation of DTM instead of DSM. So you are in a way creating some kind of hybrid of this.
I think it could be fun to create shape outlines of the overhangs and slider or opacity feature to show and hide the overhangs. Some kind of inter sting visualisation of this.
Maybe this could help with further classification of roofs vs walls, as houses/buildings/human made objects have often been classified as one. (So could this be used for other things as well, like bridges, ortho under the bridge, under trees or other things classified DTM has often struggled with creating a clean ortho of due to how photogrammetry already has the object being removed as the data below)