lasclip license necessary?

[Hugo Ledoux]

Greetings,

I would like to know if I need a license to use lasclip for a download website for the AHN2 datasets in the Netherlands. I’ve seen that you posted on a forum the difficulties you had in 1) finding the datasets and 2) downloading it. I had to fiddle a lot to access the data, so I can’t imagine how the average user would manage. 

A few years ago 3 students of mine built a system for a course similar to that of opentopography.org where the user can choose the area and the format (http://3dve.tudelft.nl/velas3d.html). I’d like to setup that system again with lastools (and lasclip) in the background. I’d use lasclip because I'd store the LAZ files on the server (each file is a tile of ~25km^2) and I'd let users draw their download area (which would be smaller than one tile, or spanning several), lasclip would permit me to have non axis-aligned rectangles and also non-convex polygons.

Would I need a license for such a case?

Cheers,
Hugo

—————————————————

Hugo Ledoux

assistant-prof GIS | delft university of technology | the netherlands

www.tudelft.nl/hledoux | h.le...@tudelft.nl

[Martin Isenburg]

Hello Hugo,

great question. The type of system you want to build can be fully implemented with batch scripted open source LAStools (e.g. laszip, lasindex, las2las, or lasmerge) without requiring any license. This assumes your system has a front end that is something like open layers or some other WMS/WMC interface where a target area can be selected and a mapping from coverage polygons to folders full of lazzed and laxxed LiDAR files. Then the backend can be implemented with a simple call to las2las or lasmerge to produce the requested area-of-interest as one compressed file for download. In fact this is what OpenTopography and a few other LiDAR servers are doing (*).

In terms of performance your best choice is las2las or lasmerge with the '-inside' command and LAZ files that have corresponding LAX files. Once LASeasy is released (you can get a rudimentary beta now) you can also apply a space-filling curve reordering to your data before indexing it spatially for lower I/O overheads for small area-of-interest queries. Each LAStools will use LAX accelerated spatial queries when the '-inside' command is used and when LAX files are present in the same folder or - as of the latest release available in beta - embedded via '-append' into the LAZ file.

The only disadvantage is that you cannot do arbitrary shapes. Only rectangles or circles. But as the functionality in OT, NOAA, USGS, and other services seem to suggest - this appears to be sufficient in practice.

Regards,

Martin @rapidlasso

(*) Hello OT staff, how much more often do I have to nudge you about describing your LAStools based back end and detail its performance as a blog post

[Hugo Ledoux]

Hello Martin,

Just a short email to say thanks. Based on your recommendations (and
your free tools) we have built an AHN2 download service (AHN2 is the
LiDAR datasets of the Netherlands, it’s now open-data: www.ahn.nl).

It’s available there:
http://3dsm.bk.tudelft.nl/matahn

We don’t offer at this point the whole of the country---because of
disk space---but we hope the government will pick up the project and
implement it (or fund us!).

Tool-wise, we use lasmerge on the server, and the performances are
reasonable. We use open-layer, a Python-based server (Flask) and
PostGIS to store the tiles’ boundaries and all the metadata. We’ll
open-source the code soon, once we’ve cleaned it.

We think it’s robust, but we invite everyone to test it and report any bugs.

Cheers,
Hugo

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