[Therion] Turning LIDAR point clouds into cave maps

[Philippe Vernant]

Hi guys,

You can also view a 3D cave from a photogrammetric survey with caveview on Karst3D. Here is the link to the cave:
https://data.oreme.org/karst3d/karst3d_map#selected_layer=karst3d_station&selected_station=61

If you visualize the 3D lox file, this is a therion survey and if you visualize the 3D file (PLY), this is downgraded photogrammetric survey.

You can easily project on a map the 3D point cloud and draw a map on it but in this case you have to work with a GIS software. The best would definitely be to have a code computing virtual survey stations to input it in therion, it could also be based on the trajectory of the camera used for the 3D photogrammetric model   

Cheers,
Phil



> On Nov 29, 2023, at 19:45, Martin Budaj <m.budaj at gmail.com> wrote:
> 
> On Wed, Nov 29, 2023 at 4:47 PM Bill Gee <bgee at campercaver.net> wrote:
> 
>> Looking at the sample files, it looks like he extracts some images from
>> the point cloud.  One of them is an overhead view and others are cross
>> sections and profiles.  He then uses these JPG images as the drawing
>> background to produce a traditional cave map.  The LiDAR scan
>> essentially replaces the in-cave sketching.  I suspect there is some
>> custom software to extract the images from the point cloud.
> 
> Indeed, the scans (combined with videogrammetry as in iPhone or iPad)
> preserve a lot of details and can be used to draw 2D maps. However,
> they can't completely replace the sketches or notes, as there is much
> information that can't be captured in the scans (air droughts, lake
> bottom etc.)
> 
>> I remember some years ago hearing about some mapping projects where the
>> survey stations were marked with small balls in a specific color.  The
>> processing software recognized that color and provided a way to connect
>> those points to known x,y,z locations - a centerline.  It was
>> fantastically expensive in both money and computer resources.
>> 
>> In a way, we do sort of the same thing with Therion.  The centerline
>> data is processed to produce a set of x,y,z coordinates.  The survey
>> stations are flagged in that data set.  Then when the sketch is drawn
>> out, we insert points of type "survey station" which are also flagged.
>> The sketch can be considered as a sort of two dimensional point cloud.
>> Therion knows how to match up the survey station points in the sketch
>> with the survey stations in the x,y,z coordinate set.  From there it can
>> morph everything around.
> 
> This is exactly the plan how to implement it in Therion, when time permits:
> 
> 1) you scan a fragment of a cave (a 3D scrap) with some survey
> stations visually marked
> 2) you assign station names as used in Therion centreline to local 3D
> coordinates in the 3D scrap
> 3) Therion warps the 3D scrap and aligns it with the centreline
> 4) ideally, Therion smoothly joins adjacent 3D scraps
> 
> The result would be a 3D model which could combine the walls captured
> from scans with those generated from the 2D scraps and LRUD data. This
> way you could progressively improve the 3D model as your LiDAR
> scanning progresses.
> 
> There is a preliminary issue for this here:
> https://github.com/therion/therion/issues/475
> 
> Martin
> 
> P.S. Here is a 50-metres dig scanned by an Apple LiDAR in around 30
> minutes: https://photos.app.goo.gl/Cvs8mej2RCqpGoj9A
> _______________________________________________
> Therion mailing list
> Therion at speleo.sk
> https://mailman.speleo.sk/listinfo/therion

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.speleo.sk/pipermail/therion/attachments/20231130/cee91ec4/attachment.htm>