[OpenStreetMap talk-lu] Announcing new 10cm imagery and our own hillshade layer in Luxembourg

Guillaume Rischard openstreetmap at stereo.lu
Tue May 12 19:34:23 UTC 2020


Hi everyone

Maybe you’ve read about the Cadastre’s February 2019 Lidar campaign? https://act.public.lu/fr/cartographie/lidar.html. This isn’t the first lidar survey in Luxembourg. If you map in the Nordstad, you might have seen the high-definition images from the 2017 prototype there.

Usually, pictures are taken around the summer solstice, to reduce the length of shadows and have better chances of good weather. This was flown in February to get better penetration through trees; and since the plane is shooting a laser, shadows aren’t a problem for lidar.

The plane flew over the whole country and shot it with a laser about 80 billion times, creating roughly 500 GB of compressed data with the details of all the measured points.

At the same time, it made photographs at about 10 cm/pixel. Here’s summer 2019 on the right at 20 cm/pixel, February 2019 on the left at 10 cm/pixel. The 10 cm imagery is of ‘technical’ quality, not corrected for distortions, like rooflines that might not look straight on the pictures.



David Morais Fereira and I then downloaded the whole thing and generated a hillshade of it. There was a lot of banging on the data with a keyboard until everything worked and rendered properly, lots of failed experiments and crashes and bugs and tons of fun.

This isn’t a traditional elevation view: we strip away the trees, but keep the buildings. We’re calling it Mapper’s Delight <https://www.youtube.com/watch?v=rKTUAESacQM>.

This is cool for forest paths, buildings under trees, cliffs, power lines, and mapping the precise position of things without distortions or the parallax effects of photo imagery. Buildings are a bit fuzzy on the edges of the roofs, but maybe we can fix this in a second version. You see the fortress well in the city park, which I think is awesome.



We’ve also generated a dtm-style hillshade of the 2017 data from the Administration de la navigation aérienne. The quality isn’t as high as the 2019 scan, but it covers bits of the neighbouring countries which we thought could be useful for mappers there.



These three layers are available for mapping by everyone today.

In JOSM, the 10 cm imagery is ‘geoportail.lu ortho technique 2019 (10cm)’ in the Imagery menu and the two hillshades are at the bottom of that menu, in the ‘elevation’ submenu.

In iD, for now, you have to add these as custom layers like this:



10 cm photos: https://wmts1.geoportail.lu/opendata/wmts/ortho_2019_winter/GLOBAL_WEBMERCATOR_4_V3/{z}/{x}/{y}.jpeg
lidar hillshade: https://lidar-hillshade-2019.openstreetmap.lu/layer/mappers_delight_lidar_hillshade_2019_reprojected/{z}/{x}/{y}.png
ana dtm : https://ana-dtm-2017.openstreetmap.lu/layer/ana_dtm_2017_hillshading/{z}/{x}/{y}.png

Finally, the hillshade makes a nice ‘pop’ effect when combined with a bit of transparency!




If you just want to explore the hillshade for hours (I do), it’s at https://lidar-hillshade-2019.openstreetmap.lu/ <https://lidar-hillshade-2019.openstreetmap.lu/>

Happy mapping, and let me know if you like it and find it useful,

Guillaume
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