Monday, May 10, 2021

3D Model of the Torhola Cave


Digitalisation of caves is proceeding! :-) I now have the first model from a bit larger cave, the Torhola cave in Lohja, southern Finland. This cave is Finland's largest karst cave, with around 100 meters of complex tunnels on 3-4 levels.

I’ve been using the new iPhone LiDAR sensors to build detailed 3D models of caves. This is the first bigger project in this series. I have hit the practical limits of the iPhone software for modelling complex structures, so the model has been recorded in four parts, which were then joined together in post-processing in a computer. On the iPhone I used the native sensors and cameras, and the Polycam software. On the computer I used Blender.

The picture above is a static side view of the model as if you were able to observe the cave from outside, but there’s an actual full 3D model behind, including textures so one can also peek inside and see what the tunnels look like etc. 

This model is a composite of four parts, turned out to be difficult to scan all in one go. This should be useful for understanding the cave, drawing cross cuts and maps, or peeking inside. But this is still very experimental, none of the softwares were really meant for this, it is difficult to get good texture video in very tight passages, there’s overlap from the different parts, and the model is also too large (600k pieces, lots of detail, but chokes my browser if I try to rotate it).

The overall process for creating a 3D model of a cave is as follows:

  1. Use the iPhone's capabilities and the Polycam applications to record a 3D model of the cave you are in. Start by creating a new model, then "record" the scene, and when finished, perform the Polycam processing as a "space".
  2. If necessary, continue the model collection by using either the "extend" capability in Polycam or create additional models.
  3. Export the resulting model(s) by using Polycam's export capability, e.g., to GLB format. Note that you will need use the non-free version of Polycam to do this. Take care of export the kind of data you need in post processing and the final model; GLB for instance includes both the model and the texture data recorded from the videos.
  4. Import the model into suitable post-processing software. Perform any corrections, merge different parts together, etc. that are needed.
  5. Use the model and the post-processing software to build any final results that you may wish generate, e.g., cross-cuts, maps, measurements, simplifications (decimation), and so on.
  6. Publish your results.
But this is still difficult. Some of the problems that I encountered:
  • Collecting high-quality video and LiDAR data is difficult in cramped cave tunnels. The sensors work best when there's a reasonable and consistent distance to the photograped walls, but I found out that I'm often too close, just centimetres from the surface.
  • Due to the nature of the complex cave, there will be a lot of situations where a "hole" is left in the model, e.g., because a cavity extends further out than the sensor can reach, and it will not be possible to crawl into the cavity. These holes cannot be distinguished algorithmically from cave entrances, and they make the processing difficult. In particular because the holes appear like fractals in small and large scale.
  • In the course of recording the Torhola cave, I experienced one failure to use Polycam's capability to extend a model; possibly due to leaving the continuation point to a tight spot where it was difficult for the software to recognise an earlier recorded part. But I've also seen this issue in some other situations, and I sometimes had to return to the starting spot of a recording. This is of course impractical in caves.
  • I also experienced one case of a firmware or sensor problem, where the iPhone indicated that I do not have rights to read the sensors. This happened in the middle of recording a part of the cave.
  • It is incredibly difficult to align manually different recordings together. I left on purpose some forms in overlapping parts that would ease alignment, but it is often difficult get the alignment done well along all axis.
  • The overlap itself is difficult to remove; my current models contain overlapping segments because of this.
  • The models are big, on the iPhone the raw data for Torhola was 4GB and over a million faces. Post-processed with Polycam, it was only 65 MB but that's still large (600k faces).
  • The large models can't easily viewed on the web interfaces using software such as model-viewer, even if they can be rotated and modified on dedicated software such as Blender.
  • Operations needed for cross sections and other useful things in Blender are designed primarily for objects. They seem to operate rather poorly for the spaces that caves represent (more than objects). I have not determined the exact causes for this, but I suspect it is due to the algorithms in Blender's Bool tool that determine what's "inside" and "outside" of an object. 
But, the results are still tremendously interesting and illuminating. And this is a fun thing to experiment with. I’ll keep exploring if this can be made to work more fully.

The raw model for Torhola is available also, both in GLB and Blender formats. Do note that these models are being processed and fine-tuned; as noted they also have several issues. On my list of things to do next is various cross-sections (see here for an example from another cave).

I have also started to maintain a directory of all 3D models I have from Finnish caves. The directory can be found here. There's also a similar directory of all cave maps, here. Both models, maps, and all other information from Finnish caves is also directly integrated to the Psgeo mapping service that the Finnish Caving Association uses. The most recent version of the software (with support for 3D models) can be accessed here. For an example of how the models are maps are visible in the map, click on this.

Read more urban exploration stories from theurbanexplorer.net, and other underground stories from planetcaver.net. Read the full Planetskier series at planetskier.net, or all blog articles from Blogspot or TGR. Photos and text (c) 2021 by Jari Arkko. All rights reserved. Thanks for Helene and Touko for accompanying me to the cave!

Monday, April 19, 2021

First cross section from a 3D model

I've been trying constructing 3D models from few caves with the LiDAR sensors in iPhone. While I've been able to rotate these models on screen easily, I also wanted to see whether I could construct more traditional maps from these models. But it has been a big learning curve to use the 3D modelling software. Today, with the help of Olli, I finally managed to make my first cross section of a cave model in Blender

I used the model from the main cave in Vihti's Rokokallio as the starting point. This is a vertical cross section of the main crack in this cave, the darker areas are the cave holes and the lighter areas are rock. With a complete model, I can make these cross sections along any axis or from any part of the cave.

A lot of work remains... but this is a nice start.

Read more urban exploration stories from theurbanexplorer.net, and other underground stories from planetcaver.net. Read the full Planetskier series at planetskier.net, or all blog articles from Blogspot or TGR. Photos and text (c) 2021 by Jari Arkko. All rights reserved.

Wednesday, March 31, 2021

More Kauniainen cave maps and 3D models

 

I spent Sunday biking and walking in Kauniainen's forests, mainly in the Kasavuori ("pile mountain") area. I wanted to visit a couple of small holes there are in the cracks and boulders of the rocky landscape on this "mountain". And draw a couple of simple maps about them, and use my new iPhone 12 Pro to record 3D models. 

This isn't to say that these are really caves. They are just small holes, enough to have one person hide from rain perhaps, not really caves in the traditional sense. But, it is all we have in Kauniainen, so in the name of documenting EVERYTHING...

Below there are some new pictures from the cave of the sunset, one of the two actually cave-like places in Kauniainen (even if these too are small). And there's a map. But most interestingly, there's a 3D model that you can rotate on your screen, here. You can also download the model if you want, in many formats. For instance, GLB format is here.





Stockmann cave #1 pictures below. And there's a map. The 3D model that you can rotate on your screen is here. The downloadable model in GLB format is here.


Stockmann cave #6 pictures are below. And there's a map. The 3D model that you can rotate on your screen is here. The downloadable model in GLB format is here.

Read more urban exploration stories from theurbanexplorer.net, and other underground stories from planetcaver.net. Read the full Planetskier series at planetskier.net, or all blog articles from Blogspot or TGR. Photos and text (c) 2021 by Jari Arkko. All rights reserved.


New cave (sort of) in Kauniainen

While cataloguing Kauniainen's tiny caves (if one can call them that), I came across another one. A small tunnel between two boulders. The tunnel part is maybe 3 meters (though with a small crack at the top for some part of that).

I call this cavelet "Kahden kiven luola" or the cave of the two rocks. The coordinates are N 60.217182 E 24.691909, and there's a map here.

Also, new since February, I try to make a 3D model of every cave I visit, using my new iPhone 12 Pro and the Polycam application. The 3D model from this cave can be viewed here. If you want to download the 3D model, it is available in GLB, OBJ, STL, and DXF formats.

Overhang part to the side of the tunnel:


3D model:

Read more urban exploration stories from theurbanexplorer.net, and other underground stories from planetcaver.net. Read the full Planetskier series at planetskier.net, or all blog articles from Blogspot or TGR. Photos and text (c) 2021 by Jari Arkko. All rights reserved.

First biking of the season!

 

Well, I had no other wheels since the car broke down...

Had a nice outing though, around Lippajärvi and Pitkäjärvi in Espoo. Good, sunny weather, even if still cold.

Read more biking stories from planetbiker.net. Read the full Planetskier series at planetskier.net, or all blog articles from Blogspot or TGR. Photos and text (c) 2021 by Jari Arkko. All rights reserved.

Friday, March 26, 2021

Looking for caves in Lohja's Linnanmäki in Karstu

The evening's excursion was to Lohja's Karstu area, in search of caves. The Linnanmäki is a high hill and cliff in Karstu, and the book Suomen Luolat notes that there are two caves on the hill. One was supposed to be inaccessible without climbing equipment. But as usual, the coordinates were inaccurate, so I ended up going around the entire hill, and I think found the other cave plus four other small roof/shelter caves.

Here are the caves and other interesting things:

  • Cave 1, high up on the cliff. I did not find this, but it has been reported in the book Suomen Luolat. Perhaps it was too dark already.
  • Cave 2, a broken devil's churn that forms a roof or shelter cave. Very nice place to camp out or sit by the fire. Nice forms. Coordinates: 60.296735, 23.930707. There's also a map and a 3D model (download GLB).







  • Cave 6, a small roof/shelter cave. Coordinates: . There's also a map.

Read more urban exploration stories from theurbanexplorer.net, and other underground stories from planetcaver.net. Read the full Planetskier series at planetskier.net, or all blog articles from Blogspot or TGR. Photos and text (c) 2021 by Jari Arkko. All rights reserved.




Thursday, March 25, 2021

Serena at the quiet hour

 

Today's outing was in Serena, a small commercial ski hill in northern Espoo. Serena combines skiing with summer activities from downhill cars to tree climbing routes, and one of the largest spas in Finland. It has been very popular... the Corona times have hit it as well, however. Nevertheless, skiing was great.

I went at the last hour, for the last 45 minutes or so. That's a bit expensive from the point of view of getting the ticket, but most people had left by then, so I was able to ski alone and not risk infections in busy lift lines. And enjoy the magnificent sunset!!!

I also liked Serena's variation, with streets, and the rolling hills run. It is a nice place to ski at!



This article has also been published at TGR. Read the full Planetskier series at planetskier.net, or all blog articles from Blogspot or TGR. Photos, videos, and text (c) 2021 by Jari Arkko.