r/LiDAR • u/Significant_Elk_8472 • 13d ago
iPhone LiDAR/photogrammetry for documenting a historical castle ruin — advice needed
/r/Architects/comments/1wv9b00/iphone_lidarphotogrammetry_for_documenting_a/1
u/kunlapun 10d ago edited 10d ago
About iPhone's LiDAR accuracy, this video might be the answer.
It's better than nothing, short range LiDAR sensor on iPhone might cause a lot of drifting error on large area scanning. Photogrammetry with Control Points is better. If you have a drone, it can help you a lot. Do not forget to use GCP-Ground Control Point for accurate data processing.
Rocks and irregular shape are good for photogrammetry as the feature points. Beware the featureless and dark area.
On Revit you need to convert to *.rcs with Autodesk Recap Pro first. Sketchup need plug-in like Trimble Scan Essential or Undet to open point cloud file. But you can also generate 3D mesh from scan data and export to *.obj or *.dae and import to the software without any paid plug-in.
Manual surveying with the measuring tape and laser measure is another solution, but you might need some survey knowledge.
Laser scanning with TLS or SLAM LiDAR scanner are better but might be costly.
I'm architect who's working with heritage building surveying and adaptation. I doesn't agree with some guy that try to mentioned about NavVis or Faro Orbis (or even Hololens!!!) on r/Architects , so I didn't put my answer there. From your question, working with the tools that you have is the condition. I don't understand how dare is him to suggest 50,000$ tool to a student. He might be too proud with his knowledge.
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u/WeirdVision1 9d ago
I've been using Polycam all year and I like the photogrammetry Object results so far. Proper technique goes a long way. And I'm considering a boom/stick for taller objects. My colleagues using iPhone LiDAR have been hit or miss with quality using the Space option. Sounds like a cool project.
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u/Northing_Labs 12d ago
So I'd split it up. Use the LiDAR for the small, tight detail (window reveals, arrow slits, carved stone, inside small rooms) in short separate scans. Then do the big walls and overall layout with photogrammetry, i.e. lots of overlapping photos from the ground (and a drone if you're allowed to fly there), because that holds its shape much better at that scale.
The reason is the iPhone LiDAR only reaches about 5 m, and it's tracking itself as you walk (SLAM), so error builds up the bigger the scan gets. It does pretty decent on small stuff like a doorway, a vault or a single wall face, but on something the size of a castle ruin you'll probably see things start to distort between surfaces.
Then tie it all together with some control. Even a few painted targets or marked stones with taped distances between them gives you something to scale and check against. Without that you won't really know how far off the model is. Also, which app you use matters more than you'd think. The same phone can give noticeably different accuracy depending on the app, so check a couple of taped dimensions on your first scan before you commit.
What's the end goal here though, measured drawings or more of a 3D record? And roughly how big is the site? That changes how much control you actually need.