Donnerstag, 21. November 2013

Mappers Blog: How to get an object height basemap with Swiss Laser Data


Update: Read Jerker Bomans comment below. Swiss authorities provide two kind of processed terrain laser data. A DTM named DOM (Digitales Oberflächen Modell) and a DEM named SwissAlti3D (Digtales Höhenmodell), so basically two surfaces, one with (DTM) one without vegetation and buildings (DEM).

For mappers the object height is a useful perspective. With OCAD11 this perspective became accessible for mappers working with Swiss Data. For those who did not upgrade I describe a work around. Acutally it is possible to achieve the perspective with the freeware OL-Laser by modifying and fusion the two datasets.


Basically the Swiss Data consists in textfiles, with one points coordinates per line.
601999.58 196042.04 622.55
Now help OL Laser to interpret this coordinate with some additional information.
601999.58 196042.04 622.55 9 2 1 1
This by adding 4 values for intensity, number of returns, return number, classification behind the coordinates. In the example you have the signature for "surface": intensitiy 9, first return of two, unclassified. This signature you can add to the coordinates of the DOM.

For the DEM the signature looks like this
600005.00 196001.00 762.11 31 2 2 2
Here I choose an intensity  of 31 (just an arbitrary value). It is the second return of two (last return) and the point is classified as ground.

That was it: Modify the lines, fusion the two files and then proceed to OL-Laser.

 fig.1. Object height perspective of "Gurten Nordhang" produced with OL Laser.

By the way. The similar trick also makes the Swiss Data useable to the automatic map generator karttapullautin, only that the order in the signature to add is different. Here it is x,y,z,classification,returns,return nro, intensity. You therefore got to switch the places of classification and intensity.
600005.00 196001.00 762.112 2 2 31 (ground)
601999.58 196042.04 622.551 2 1 9 (surface)

fig.2. Not optimized karttapullautin map combined with vector data of openstreetmap of the same area.

1 Kommentar:

Anonym hat gesagt…

Hi Martin
If you send me one couple of your (Swiss) files, one DEM and one DTM that fits together, i will try to support them without needing any modification.

/jerker
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