Bled, Slovenia--Crossing off Place on Bucket List

 One of my goals over the past decade has been to see the castle in Bled, Slovenia.  It started when I wrote a paper for a conference on castles in the clouds, with views of castles from lidar point clouds.  Besides a bit of fun, castles show the challenges in removing buildings to create digital terrain models, since "big" buildings present many challenges.  This year we got to Bled.  We hiked entirely around the lake, with ever changing views of the castle, mountains, and clouds.

The first paper to use the Bled data showed three different visualizations of the castle, all using the point cloud.  Slovenia has one of the best classifications for their free lidar; many countries only break out ground and other.

Two later papers used slightly different versions of the same cross section comparing the lidar (~1 m spacing) with the global DEMs with about 30 m spacing.  These view the castle from the lake side to the south; the views above are from the north.

For no very good reasons, one of the global DEMs records points that are about 15 m displaced from those in the others.  The elevations thus do not match up very well.  While I understood from maps and digital data that the castle was perched on a very steep hill, my understanding increased dramatically when we saw the castle and hiked up to it (on the back side, where there is a road).

References

Guth, P.L.; Van Niekerk, A.; Grohmann, C.H.; Muller, J.-P.; Hawker, L.; Florinsky, I.V.; Gesch, D.; Reuter, H.I.; Herrera-Cruz, V.; Riazanoff, S.; López-Vázquez, C.; Carabajal, C.C.; Albinet, C.; Strobl, P. Digital Elevation Models: Terminology and Definitions. Remote Sens. 2021, 13, 3581. https://doi.org/10.3390/rs13183581

Guth, P. L., & Geoffroy, T. M. (2021). LiDAR point cloud and ICESat-2 evaluation of 1 second global digital elevation models: Copernicus wins. Transactions in GIS, 25, 2245– 2261. https://doi.org/10.1111/tgis.12825

Guth, P.L., 2018, Castles in the Clouds: LiDAR for Historical Study and Terrain Analysis: Scientia Militaria - South African Journal of Military Studies, Vol 46, No 1, p.79-95, DOI: https://doi.org/10.5787/46-1-1226