We got a little note from Vítězslav Moudrý from CULS pointing out that the Geodesy, Cartography and Cadastre Authority of the Slovak Republic has started releasing LiDAR as open data on their interactive Web portal. Congratulations, Slovakia!!! Welcome to the Open Data Party!!! We managed to download some data starting from this Web portal link and describe the process of obtaining LiDAR data from the Low Tatras mountain range in central Slovakia with pictures below.
(1) click the new “data export” link
(2) change the export selection to “Shape”
(3) change the file format to “LAZ”
(4) zoom to a colored area-of-interest
(5) zoom further and draw a nice polygon
(6) edit polygon into nice shape and realize heart is red because area is too big
(7) zoom further and draw polygon smaller than 2 square kilometer
(8) when polygon turns green, accept license, enter email address and export
(9) short wait and you get download link to such an archive
(10) license conditions: PDF auto-translated from Slovak to English
(11) LiDAR are spatially indexed flight lines clipped to area-of-interest
(12) all return density: blue = 20 and red = 50 returns per square meter
lasgrid -i LowTatras\*.laz -merged ^
-step 2 -point_density_16bit ^
-false -set_min_max 20 50 ^
-o LowTatras\density_all_returns_20_50.png
(13) last return density: blue = 4 and red = 40 last returns per square meter
lasgrid -i LowTatras\*.laz -merged ^
-keep_last ^
-step 2 -point_density_16bit ^
-false -set_min_max 4 40 ^
-o LowTatras\density_last_returns_4_40.png
(14) ground return density: blue = 4 and red = 40 ground returns per square meter
lasgrid -i LowTatras\*.laz -merged ^
-keep_classification 2 ^
-step 2 -point_density_16bit ^
-false -set_min_max 4 40 ^
-o LowTatras\density_ground_returns_4_40.png
(15) flight line difference image: white <= +/- 10 cm and red/blue >= +/- 20 cm
lasoverlap -i LowTatras\*.laz -faf ^
-drop_classification 7 18 ^
-min_diff 0.1 -max_diff 0.2 ^
-o LowTatras\overlap_10cm_20cm.png
Finally we compute a DSM and a corresponding DTM using the already existing ground classification with BLAST using the command sequence shown below.
lasthin -i LowTatras\*.laz -merged ^
-drop_classification 7 18 ^
-step 0.5 -highest ^
-o LowTatras\highest_50cm.laz
blast2dem -i LowTatras\highest_50cm.laz ^
-hillshade ^
-o LowTatras -o dsm_1m_hillshaded.png
blast2dem -i LowTatras\*.laz -merged ^
-keep_classification 2 ^
-thin_with_grid 0.5 ^
-hillshade ^
-o LowTatras\dtm_1m_hillshaded.png
We thank the Geodesy, Cartography and Cadastre Authority of the Slovak Republic for providing their LiDAR as open data for both commercial and non-commercial purposes and name the source of the data used above (as the license requires) as the Office of Geodesy, Cartography and Cadastre of the Slovak Republic (GCCA SR) or – in Slovak – the Úrad geodézie, kartografie a katastra Slovenskej republiky (ÚGKK SR).
Which European country goes next? Czech Republic? Poland? Hungary? Switzerland?
Switzerland will not be next as the cantons are in charge of administering their own geo-data. Some cantons share their LiDAR as open data for quite a while (Zurich, Aargau, Basel-Land, Graubünden, Geneva), others don’t.