[HN Gopher] Show HN: High-resolution surface analysis with Lidar...
       ___________________________________________________________________
        
       Show HN: High-resolution surface analysis with Lidar data
        
       Author : folli
       Score  : 61 points
       Date   : 2025-05-21 20:40 UTC (3 days ago)
        
 (HTM) web link (github.com)
 (TXT) w3m dump (github.com)
        
       | schobi wrote:
       | Thanks for sharing!
       | 
       | The description confused me, as it describes the use of a real
       | Lidar measurements to detect "change" in the terrain. But
       | certainly, it can't be a temporal change before and after... to
       | detect medieval settings in the data. Is the area still changing
       | differentlybetween scans over multi year's? I don't think so.
       | 
       | I think this is visualization code highlighting natural VS. human
       | train structures, at known locations of old settlements? Showing
       | different approaches on how to visualize the man-made heights in
       | the terrain.
       | 
       | But still, I'm lost how this could help finding new ones..
        
         | folli wrote:
         | I think the examples should make it more clear. Thanks to the
         | high resolution of the data, you can see subtle changes in the
         | slope (aka relief aka microtopography) that could hint to
         | underlying remains of human settlements (usually some
         | suspicious geometric patterns that you would not expect in a
         | natural terrain).
         | 
         | See also here for an in-depth discussion on the potential use
         | of such data: https://www.mdpi.com/2072-4292/15/6/1569
         | 
         | How do you suggest to change the description to make it less
         | confusing?
        
           | folli wrote:
           | Here's another article about the use of such data in South
           | America:
           | https://www.nationalgeographic.com/history/article/maya-
           | lase...
           | 
           | Of course, nothing so exciting to be discovered in
           | Switzerland anymore ;)
        
       | weinzierl wrote:
       | _" Buildings and vegetation are removed, revealing the underlying
       | topography."_
       | 
       | I understand how vegetation could be removed, but buildings? How
       | is that accomplished?
        
         | folli wrote:
         | SwissTopo has a separate dataset of buildings and structures in
         | Switzerland, so they basically just subtract it from the LiDAR
         | data.
        
         | Geo_ge wrote:
         | A raw point cloud is run through a series of processing steps
         | to label each point with a class, e.g. "Ground",
         | "Low/Medium/High Vegetation", "Building", "Transmission Tower",
         | etc.
         | 
         | https://desktop.arcgis.com/en/arcmap/latest/manage-data/las-...
         | 
         | There will be a different algorithm for each feature class. For
         | example, points that are part of a building might be identified
         | by finding groups of points that form a very flat surface. ML
         | models can also do this based on training data.
         | 
         | https://pro.arcgis.com/en/pro-app/latest/tool-reference/3d-a...
         | 
         | The final digital elevation model (DEM) is then just taking the
         | "Ground" class from the classified point cloud and using them
         | to triangulate a surface. This differs from a digital surface
         | model (DSM), which will triangulate a surface based on
         | ground+building+vegetation points.
        
         | thebruce87m wrote:
         | Removing vegetation seems like a harder problem than buildings.
         | Buildings generally have cuboids and other standard shapes, but
         | how do you determine the difference between small trees, big
         | trees, bracken etc?
         | 
         | It the Scotland we have heather that can coat hills but I'm not
         | sure that you'd be able to tell the difference between that and
         | a forest canopy to assume a height and then subtract. Maybe
         | there's more than the point cloud to work with.
        
           | Geo_ge wrote:
           | Aerial survey LiDAR can process multiple returns from a
           | single laser pulse. So, some energy might be reflected back
           | from a leaf, but some energy will pass through (or around)
           | the leaf, hit the ground, then reflect back to the sensor.
           | Some systems can record 5+ points from a single laser pulse.
           | 
           | With this information, you can filter the point cloud to only
           | include points from the final return, which is likely to be
           | the ground/a solid surface unless the vegetation is very
           | dense.
        
             | 0_____0 wrote:
             | You don't even need multireturn, typically your point cloud
             | will have points from the tree or whatever plus some that
             | returned from the structure behind it.
        
       | lyu07282 wrote:
       | > LiDAR has some interesting use cases in archaeology (Caspari,
       | 2023), particularly for uncovering man-made structures that are
       | hidden beneath vegetation or subtle terrain changes. It allows
       | archaeologists to identify features such as ancient roads, walls,
       | building foundations, and agricultural terraces that may be
       | invisible to the naked eye or conventional aerial photography.
       | 
       | Wasn't this also how the cities in the Amazon were discovered as
       | well? These maps are fascinating. I can see ancient structures
       | everywhere! Then again I'm not a trained archeologist.
        
       ___________________________________________________________________
       (page generated 2025-05-24 23:02 UTC)