Aesthetic LiDAR Art in “REBIRTH”

Director Patryk Kizny shows us – once more – aesthetically pleasing visuals in his latest short “REBIRTH“. Already known for turning high-dynamic range (HDR) imagery captured in historic buildings into a stunning piece of art with his earlier short film “The Chapel“, Patryk returns to the screens with a larger project that integrates both LiDAR and HDR images. His new 14 minute short film can be watched online via this link. Below a few still images from the beautiful movie to make sure you really watch it … (-: … turn on the audio for narration and soundtrack. There used to also be a neat timelapse video about the “scanning of the temple” by EKG Baukultur with a Faro scanner.

rebirth_poster

LiDAR heights of burial mounds and cairns

[contributed by guest blogger Lars Forseth]

Archaeologists are increasingly finding ALS/LiDAR useful for making better surveys of archaeological sites and monuments. This is also done where these sites are in danger of being developed, and thus destroyed, see i.e (Risbøl 2011; Gustavsen et al. 2013). Norwegian archaeologists at several county councils and museums have detected unknown sites in woodland or areas previously not surveyed. LiDAR is now available for large areas, as the national mapping authority of Norway, Statens Kartverk, is using this data as a source for generating elevation and contour maps.

aerial view of a mound in North-Trøndelag

aerial view of a mound in North-Trøndelag

Working in North-Trøndelag county, my colleague Kristin Foosnæs at NTNU and I have embarked on a project to create a survey of the larger burial mounds and burial cairns of the county. North-Trøndelag seems to have an unusual large amount of such mounds larger than 20 meters (462 such are so far identified, far more than in any other county). We have gathered exact survey data for a sample of 2900 mounds/cairns. For these we have the exact polygon describing the area of the mounds. LiDAR and LAStools have been extensively used in the creation of this database.

the same  mound seen from the ground

the same mound seen from the ground

The height of the monuments however could only be gathered from the national monuments and sites database where the heights are stored as text. These were gathered by field surveys in the 1970s to 1990s. Then the only tools available to archaeologists for estimating the height were yardsticks or soil probes. Mapping the sites was done on aerial photos at a scale of 1:16.000. The height data gathered from the database is very variable in quality, which has to do with how they were generated. Mostly those that did the original surveys had to estimate the height of the monuments.

a first-return DSM and a ground-return DTM of the same mound

a first-return DSM and a ground-return DTM of the same mound

This summer I discovered that the lascanopy tool of LAStools could measure the min/max elevation for an area-of-interest. Using lascanopy I generated a csv report of elevations (min/max) within a polygon in a shapefile:

lascanopy -lof steinkjer.txt ^
          -keep_class 2 ^
          -lop tessem.shp ^
          -height_offset -1000 ^
          -centroids -min -max ^
          -o tessem.csv

Here I’m inputting a text file ‘steinkjer.txt’ with the list of LAS files to be queried and a shapefile ‘tessem.shp’ with the polygons of the mounds I want to know the height above the ground for. The output ‘tessem.csv’ looks like this:

index,min_x,min_y,max_x,max_y,centroid_x,centroid_y,min,max
0,616277.76,7108569.01,616290.33,7108581.37,616284.04,7108575.19,76.72,77.98
1,616292.40,7108572.37,616299.98,7108580.46,616296.19,7108576.41,77.83,78.96
2,616310.04,7108585.13,616320.96,7108596.96,616315.50,7108591.05,79.93,81.15
3,616714.65,7108371.35,616734.75,7108392.03,616724.70,7108381.69,83.47,86.73
4,616681.74,7108412.71,616699.80,7108429.61,616690.77,7108421.16,86.13,87.97
5,616672.13,7108436.30,616694.56,7108453.78,616683.34,7108445.04,86.55,89.19
6,616666.01,7108449.99,616696.89,7108475.04,616681.45,7108462.52,85.74,90.79
7,616665.14,7108471.25,616687.86,7108494.26,616676.50,7108482.76,86.81,90.35
8,616673.88,7108488.44,616691.35,7108505.91,616682.61,7108497.18,86.72,89.35
9,616695.43,7108602.90,616724.26,7108632.90,616709.85,7108617.90,81.18,85.27
10,617066.09,7108807.01,617080.97,7108819.01,617073.53,7108813.01,87.44,89.59
11,616010.62,7108764.98,616025.46,7108780.39,616018.04,7108772.68,88.3,90.78
12,621229.46,7111180.27,621246.66,7111197.69,621238.06,7111188.98,111.3,112.86
13,621196.44,7111192.72,621216.57,7111208.55,621206.50,7111200.63,110.18,112.08
14,621183.77,7111206.97,621206.39,7111226.65,621195.08,7111216.81,109.69,111.89

The resulting CSV file can be imported to QGIS with the centroid x/y as point location. In QGIS I can then generate a spatial join between the CSV file and the shapefile containing the surveyed mounds/cairns. Then using the field calculator on the table, I can compute the height as a difference of max and min elevation for the each mound/cairn. About 2600 of the 2900 monuments could get their height measured using lascanopy.

The results are shown in the three plots. These have been generated in R and ggplot2. The figure below shows the diameter plotted against the height gathered by lascanopy.

Diameter plotted against height

Diameter plotted against height

Height and diameter correspond to a large degree. One marked difference between mounds and cairns is that some of the larger mounds are lower than their expected height. This can have two explanations; one is that mounds are more likely to be affected by cultivation activities (i.e. they were plowed over by farmers) that have reduced their height. Mounds are more likely to be situated close to farms, while cairns are more likely to be sited along the coast or on hills.

histogram of diameter of monuments

histogram of diameter of monuments

The above histogram of the diameters of the monuments shows a skewing of the data towards the left. Mounds above 20 m of diameter are considered to be large, while those above 40 m are called “kongshauger” or “Kings mounds”. There are 19 such in North-Trøndelag. A normal – Gaussian – curve is fitted over the histogram.

histogram of heights of monuments

histogram of heights of monuments

Finally, the above histogram of the heights – as measured by lascanopy – for aproximately 2600 monuments. This shows that the maximum height lies at about 12.5 meters. The histogram of heights is again skewed to the left. The large mounds mostly seems to be above 20 m of diameter and above 4 m of height.

References:
Gustavsen, L., Paasche, K. 1964-, & Risbøl, O. 1963. 2013. Arkeologiske undersøkelser: vurdering av nyere avanserte arkeologiske registreringsmetoder. Oslo: Statens vegvesen.
Risbøl, O. 1963-. 2011. Flybåren laserskanning til bruk i forskning og til forvaltning av kulturminner og kulturmiljøer: dokumentasjon og overvåking av kulturminner. Oslo: NIKU.

locating German bunkers concealed by canopy

After accidentally finding Russian tanks in Polish forests I was curious to see if there was something else hiding under the forest canopy. Remember, I randomly picked a 500 by 500 meter LiDAR tile as example data to introduce a group of forestry students to LiDAR processing with LAStools during the ForseenPOMERANIA camp. After extracting ground points with “lasground.exe“, strange bumps appeared in the bare-earth hillshades generated with “las2dem.exe” for terrain that was supposed to be completely flat … they turned out to be Russian WW-II positions.

I met Achim when returning to teach the next two groups of students. His hobby is a mix between geo-caching and conflict-archaeology: locating old German bunkers based on approximate coordinates available in historic records and tourist maps and then mapping them precisely with GPS. Achim had a list of longitude/latitude positions as KML files where he was planning to search for known bunkers. I used “lasboundary.exe” to create polygonal outlines in KML format for all areas where we had LiDAR from the forestry project. With Google Earth it was easy to find overlaps between his target areas and our LiDAR coverage.

I extracted the ground points and created bare-earth DTMs of the relevant area with a LAStools batch processing pipeline of “lastile.exe“, “lasground.exe” and “las2dem.exe” and used “blast2dem.exe” to create a seamless hillshading with proper KML referencing (here is a tutorial for such a pipeline). What I found was pretty amazing.

At first glance it looks like a maze of little creeks that are running alongside the ridges of the hillsides but we know that water flows downhill and not “along-hill”. What we see is a network of WW-II trenches that are connecting the bunkers Achim is looking for. A closer look also reveals the likely location of those bunkers.

I placed a pin on each of them and exported their longitude and latitude coordinates for upload into Achim’s GPS device. The next day we set out to verify our LiDAR findings on the ground.

It was a rainy day. Walking through this maze of green and overgrown trenches from one moss-covered bunker ruin to the next felt oddly quiet and peaceful. Achim explained that these bunkers were originally built to defend the border with Poland – long before the Second World War broke out. Only when Russian soldiers were advancing on Germany after the collapse of the Eastern front, the young boys of the Hitler Youth were commanded to dig this network of trenches in order to fortify the bunker and stop enemy lines from gaining ground. After the war the Russians blew up all bunkers that were facing East so that their troops would not ever have to face them again.

finding Russian tanks in Polish forests

In August and September of 2013, I spent several weeks in the woods of Poland teaching LiDAR processing with LAStools to four groups of forestry students as part of the ForseenPOMERANIA camp. Wanting to be locally relevant, I switched my usual training data for a 500 by 500 meter tile of LiDAR from nearby forest that I randomly clipped from the massive amount of data that was handed to me. I did not do a test run before the workshop because I trust my algorithms. Imagine the shock when – during my live demo on the first day of teaching – the bare-earth points extracted with “lasground.exe” showed unexpected distortions: large, weird-looking bumps appeared when generating a hillshade with “las2dem.exe” for terrain that was completely flat.

Turns out we found remains of  WW II tank positions. We later drove to the site and verified our findings on the ground.

At that time I had generated a larger 6km by 6km bare-earth hillshade of the area which I showed to a local ranger who pointed out the defensive moat that was dug to stop tanks from advancing. It also became clear that the tanks were aiming towards the north-west, hence at Germany, suggesting they were Russian positions. When you follow the direction the line of tanks are pointing at you can find craters and evidence of the German trenches in the hills.

This was in August. On my return in September, I would meet a retired gentleman whose hobby was a variation of geo-caching: finding old German bunkers and pin-pointing their exact GPS coordinates starting from rough locations on old maps available in souvenir shops and historic records. He confirmed that the positions we found were from late WW-II when Russian forces were advancing fast towards the Eastern seaboard of Germany but were digging in whenever encountering pockets of strong resistance. The saga continues here

Can you copyright LiDAR?

UPDATE: The situation has changed. Make sure you also read this.

A few weeks ago, I wanted to demonstrate how geometric compression can shorten download times for online dissemination of 3D archeological artifacts. The demo failed. My web page was gone. The web admin told me later that he had to delete it after receiving an email from a director at CyArk stating that I was “[…] hosting unauthorized content from CyArk […] ” and that “[…] Dr. Isenburg gained unauthorized access to our information and the re-posted it to his webpage […]”. Bummer. Unintentionally, I had become “the raider of the CyArk”. A point plunderer. A LiDAR looter. A scan scrounger. A laser pirate … arrr … (-;

How did I fall so low? After reading this LiDAR news article about CyArk’s new online 3D viewer I invested serious time into understanding their content delivery system and suggested how to shorten download times as I had done a lot of prior research on this particular topic (see this, this, this or this page). So, I created several interactive java-based web pages for them to demonstrate how – with some quantization, simple prediction, and clever scripting – more web-efficient 3D content might be possible. I did these experiments with their data sets to allow an apples-to-apples comparison: a point model (Ti’kal) and a mesh model (Mount Rushmore).

cyark_mount_rushmore_small

After a long technical exchange the person at CyArk suddenly demanded that I take down the compressed content. I was surprised and asked why I should have to delete these illustrative examples on 3D compression that represented a significant investment in volunteered time and energy.

Me: “What you mean with take down? Delete it from my webpages? But I am using it as a purely educational example for scanner precision and coordinate resolution. I am not promoting it in any context that would interfere with the mission of CyArk. I do not quite follow the imperative here. Aren’t you a non-profit site dedicated to science and education? And anyone could download those points clouds from your site just the way I did it. It’s not rocket science … (-:”

Person at CyArk: “And, yes, to clarify my request, I would like you to delete any content from your server or webpages. Sorry if I was vague. Thanks!”

Me: “I believe I am in accordance with both Ben (Kacyra)’s vision and the creative commons license with my educational use of the 3D content (see http://archive.cyark.org/copyright). Is there something I am missing?”

I considered myself well informed about CyArk’s mission on providing open access to 3D data for research, education, and virtual tourism through various media such as Wikipedia and Ben Kacyra’s visionary TED talk. I assumed that my creative commons argument had resonated because I did not hear back from them. I only realized that CyArk was not interested in explaining their licensing but simply had my pages removed when I tried to access this demo.

A few days ago I saw Tom Greaves, executive director at CyArk, commenting “Sweeeet use of CyArk data.” on their blog entry which describes the creation of a sugary fudge replica of Ti’kal – the very same data set that I had been using – for the launch event of a new sugar series by British-based multinational agribusiness Tate & Lyle.

Tik’al Fudge Cake made with golden caster sugar, over 80 cm tall

I like to have fun with LiDAR and appreciate the educational factor of such events. Yet I wonder whether the Guatemalan people would be that much happier to see their ancient cultural heritage presented as a piece of cake to promote a new line of sugars than to see it used as a demo on how to Web-optimize 3D content … (-;

I took this as an opportunity to – once more – inquire about the creative commons license of CyArk and I finally received an answer from Tom.

Dear Dr. Isenburg,

Please understand that only some of […]     […] have any questions.

Sincerely,
Tom Greaves

Executive Director
CyArk

Unfortunately Tom did “not recall giving” me his “permission to publish” his “private correspondence” as he pointed out shortly after this blog article went live, so I had to remove the reprint of his email. It essentially said that much of the data collected by CyArk remains property of the site owners and that Cake for Breakfast obtained permission to use the 3D scan as the secret ingredient for their Mayan bake job.

copyright cartoon

After inquiring with Tom “So which models are creative commons and which not?” I quickly got the surprising response from Tom that: “None of our 3D point cloud is available under Creative Commons. Only some of the 2D image data is covered by this.

Now this is certainly not what I had been reading into their press releases and news articles. The data-generous openness in access to 3D data that is advertised for example on their mission statement: “Digital Preservation is ‘Preserving cultural heritage sites through collecting, archiving and providing open access to data created by 3D laser scanning, digital modeling, and other state-of-the-art technologies,’ the CyArk Mission.” is apparently not the practiced reality.

So I asked in my LAStools user forum about the experiences of others: What are the most and least permitting licenses for such data and what do they mean in practice? How do I know what is open and what not? Can you help clarifying what “creative commons” licensing means and what it allows and forbids so I don’t violate anyone’s license in the future. This sparked discussions with interesting outcomes:

  1. the creative commons (non-commercial) license is useless
    The folks behind @OpenAccessArch picked up the story to provide their view of the particularities of the creative commons (non-commercial) license used by CyArk in a long blog post titled “Creative Commons Non-commercial A Cruel Joke.
  2. it is in general not possible to copyright a LiDAR scan
    Doug Rocks-Macqueen from @OpenAccessArch also started the fundamental discussion whether it is even possible to copyright a LiDAR scan in the first place. Apparently not – at least not for an object whose copyright has already expired and for details read this message thread. His closing argument was that in this legal battle between Meshwerks, Inc. and Toyota Motor Sales U.S.A., Inc. the Court of Appeals affirmed the district court’s opinion that “3D models of physical objects, if faithfully and accurately representing the original, are not original enough to warrant copyright protection.”
  3. do not engage in open-washing … (-:
    In CyArk’s defense it needs to be said that there is probably a collision between their vision and the contract terms specified by the different site owners that they have to respect in order to get the permission to scan a site. What is lacking are clear terms of use in their communications and proper protection mechanisms. The academic pioneers of 3D scanning at Stanford university had to deal with similar issues during their Digital Michelangelo Project and created ScanView: a secure client / server rendering system that permits users to examine 3D models, but not extract the underlying data. In summary: do not claim your data is open and allow access to it when it is not.

With all the publicity I was worried that my little rabble rousing might be perceived as disruptive instead of constructive by the community until someone reassured me that: “I think we’re all quite happy that the discussion is happening. Between you and me, CyArk have a reputation as being rather less open with their data than their publicity would suggest.” … (-;

Martin @rapidlasso

PS: Be aware that all comments to this article will be considered “creative commons”. Or maybe not … (-;

cyark_tikal_sugarcubes_400The (loosely related) image shown above was obtained here and is courtesy of CyArk. I assume this use is allowed under their copyright and does not violate the creative commons (non-commercial) license … (-;

Addendum (May 1st, 2013): As a result of this article CyArk not only updated their copyright notice to exclude point clouds from the Creative Commons license but also added a very clear data use policy statement.