Author Topic: Can LiDAR Help Produce Cave Surveys  (Read 353 times)

Offline Swallowneck

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Can LiDAR Help Produce Cave Surveys
« on: May 20, 2020, 09:42:30 am »
With the recent activity on UK Caving regarding Lidar and cave surveying, let get a new thread going on the this subject and possibly others such as Photogrametry.

Historically Lidar kit has been stupidly expensive and has not really been within the realms of your average cavers budget.
However with the arrival of much cheaper Lidar units such as that designed into the Caveatron device, owning such equipment is now a possibility for most people. (if you can build one that is)

For the last year or so I and several others have been slowly trying to see what we can do with Lidar data top produce what we would call a normal survey i.e a plan and elevation on paper. Some success has been had and have even combined trad & Lidar data.

The Lidar data produces some great 3D cave images with fly troughs etc, think Roo Walters amazing film of Tham Luang cave but can it cut the mustard when it come to producing a traditional survey? I personally think not at the moment but maybe the combined Lidar/Disto Caveatron device is a game changer.

Lets get discussing.


 

Offline Ouan

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Re: Can LiDAR Help Produce Cave Surveys
« Reply #1 on: May 20, 2020, 10:21:44 am »
Roo's Tham Luang LIDAR was used in the drawing of this survey
https://www.thailandcaves.shepton.org.uk/files/cavesurveys/chiangrai/tham-luang-np-complete.png

The LIDAR, viewed from directly above, was overlaid on the survey centre-line to get a detailed passage outline. However, the other details e.g. floor deposits, formations, etc. came from the traditional survey notes. The LIDAR survey was also handy for spotting features in the roof, such as the 40 m high aven that I had missed when surveying the passage.


Offline mrodoc

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Re: Can LiDAR Help Produce Cave Surveys
« Reply #2 on: May 20, 2020, 10:27:55 am »
fly troughs etc,

Drinking troughs (or are they bathing troughs) for flies. Who'da thought it! Sorry, typo sprang out at me to deliver some surreal images.

Offline Bob Mehew

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Re: Can LiDAR Help Produce Cave Surveys
« Reply #3 on: May 20, 2020, 10:55:09 am »
It may be worth reflecting that as I understand it, the Caveatron outputs both compass, clino & distance between marked stations in the survey and separately the LIDAR data which is 'hung onto' that survey data.  You would need to discuss with the likes of Dave254 about the precise nature of the data.

Offline JohnMCooper

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Re: Can LiDAR Help Produce Cave Surveys
« Reply #4 on: May 20, 2020, 11:05:26 am »
Quote
typo sprang out at me
Now that's not something I would have thought coming from you mrodoc :lol:

Offline Swallowneck

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Re: Can LiDAR Help Produce Cave Surveys
« Reply #5 on: May 20, 2020, 12:33:50 pm »
Quote
Roo's Tham Luang LIDAR was used in the drawing of this survey
https://www.thailandcaves.shepton.org.uk/files/cavesurveys/chiangrai/tham-luang-np-complete.png

The LIDAR, viewed from directly above, was overlaid on the survey centre-line to get a detailed passage outline. However, the other details e.g. floor deposits, formations, etc. came from the traditional survey notes. The LIDAR survey was also handy for spotting features in the roof, such as the 40 m high aven that I had missed when surveying the passage.


I've done similar with some of Roo's data but if you have to trad survey to get the floor detail that means you have to go though the cave twice which seems a bit daft or scan and survey at the same time which is where the Caveatron may come in. I have been trying to slice the point clouds at floor level to get the outline of big boulders and then dropping that into Therion or cad as a sort of different layer which is a faff but it's doable but it will not really help with smaller features and water etc.

It will be interesting to see how the Caveatron software deals with scan alignments, I assume it just hangs the scans off the survey stations. I know that using using normal Lidar equipment such as a Riegl device aligning the individual scans can consume quite a bit of time.

One other thing I have a problem with when using a point cloud for a survey is what exactly is the passage outline when viewed from above, as all you can see are the maximum extents at all levels picked out from line of sight by the laser which is not usually helpful. I normally slice the data at a level that gives a good representation of the passage as seen by a caver moving though it. You could argue the same when using a disto but as you are actually there when measuring and sketching I think you tend to make a better job of representing the passage.

You can do an awful lot with the point cloud data and the detail is amazing but to produce a regular survey I think the disto/pda/phone combo is still the quickest and easiest method.



 

Offline Bob Mehew

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Re: Can LiDAR Help Produce Cave Surveys
« Reply #6 on: May 20, 2020, 12:47:39 pm »
It will be interesting to see how the Caveatron software deals with scan alignments, I assume it just hangs the scans off the survey stations.
Have a read of http://www.caveatron.com/documents/Caveatron_Paper_Proceedings_ICS_2017.pdf

Offline maxf

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Re: Can LiDAR Help Produce Cave Surveys
« Reply #7 on: May 20, 2020, 10:51:38 pm »
Lidar/ laser scan data sets can reveal much more detail that a normal survey can, below is an image of Redcliffe caves (actually a mine) in Bristol with the difference between floor and ceiling height indicted by colour (see reference bar on the right). The red circular areas are actual linked to the road above via manhole covers.



Anybody who had been and done crawling bits will be familiar with the changes in passage height clearly displayed by this image.

Perhaps we shouldn't be looking to make laser data conform to traditional survey standards but updating the normal standards to match the every increasing amount of data available allowing the user to better visualise the cave or structure.


Offline PeteHall

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Re: Can LiDAR Help Produce Cave Surveys
« Reply #8 on: May 20, 2020, 11:10:14 pm »
This looks a bit like an orienteering map, where different colours indicate different terrain/ ease of movement. Could also be very useful looking for trends in the cave formation and possible dig sites.

While there are doubtless many benefits to this sort of presentation of data, it does not convey all the same information as a "traditional" survey. It is a good addition, rather than an alternative I think.

If we were dealing with electronic documents, being able to switch between layers that represent different data would be really useful, but this obviously doesn't work with a paper survey, unless you printed it on several layers of tracing paper  :smartass:
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