lasvdatum

[Möst, Karin (LDBV)]

Hello Jochen,

I want to change our production from some inhouse java programs to another workflow. In this context I tried to use lasvdatum.
My pointcloud is UTM32 (epsg 25832), ellipsoidal height. The grid for vertical differences is in .gcb format.

Is there a way to run this in lasvdatum?

My Code is:

lasvdatum ^
-i *.la* ^
-epsg 25832 ^
-vgrid HOEHE_ELL_NHN-GCG2011b-10.gcb ^
-cpu64 ^
-odir NN

I get an error message:

ERROR: reading ncol 0 of row 249858
ERROR: failed to load vgrid difference value file 'HOEHE_ELL_NHN-GCG2011b-10.gcb'

Maybe I have to convert the .gcb format to some other format?


Kind regards
Karin

[Jochen Rapidlasso]

Hi Karin,

lasvdatum does not use the Geocon Combined Binary (*.gcb) format right now.
You have to use the *.gtx format. 

We may can add a support for gca/gcb, but before we need to
check this:

• is it semantic possible and useful?
• is there a demand to do this by >1 users?
• is there shure no other tool who can do this easy (we do not want to program something which is there already)

So also other lastools/lasvdatum users: Please give your comment to this.

Thanks and best regards,

Jochen @rapidlasso

[Michael Perdue]

Hi Karin,

lasvdatum requires geoids to be in gtx format. GDAL is capable of creating gtx format geoids, but I'm unfamiliar with the gcb format and cant say whether GDAL can read it or not.

If you find that gdal_translate is not able to ingest your source geoid, you can try perusing through the projlib add on resource files. Most of them are distributed in gtx format.

Cheers,

Mike

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[Möst, Karin (LDBV)]

Hi Mike, hi Jochen,

 

thank you, I will give GDAL a try.

The gcb format is provided by the BKG (this is the German Federal Agency for Cartography and Geodesy)

I heard from a colleague they provide Geotiff as a new format. Maybe this could be a format to implement in lasvdatum, since it might be more common?

 

Regards

Karin

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[Jochen Rapidlasso]

Hi Karin,

yes, I would prefer GeoTIFF. 

Could you send me a sample [file / file link] by mail?

Thanks,

Jochen @rapidlasso

[Jorge Delgado García]

If you obtain a GeoTIFF file you can try to use this tool

GTX to TIFF Converter Online - MyGeodata Cloud

In order to convert into a GXT file and use in lasvdatum.

Jorge

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[Möst, Karin (LDBV)]

Hi Jochen,

 

you can download sample data from https://gdz.bkg.bund.de/index.php/default/quasigeoid-der-bundesrepublik-deutschland-quasigeoid.html

There are different formats in the zip-file.

 

Regards

Karin

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[Michael Perdue]

Hi Karin,

If you can get the geoids in geotiff format, then it is trivial to convert them to gtx format. Simply run:

gdal_translate -of 'GTX' MyGeoid.tif MyGeoid.gtx

...and you're done.

Note that some countries do unusual things with the geoids they release. For example, Canada likes to release their geoids with undulation values in mm instead of m, and the USGS likes to release theirs with longitude values ranging from 0/360 rather than -180/+180. Lastools seems to be fine with 0/360 but other software packages have issues. Canadian geoids do need to be rescaled to m before conversion to GTX format or they will not work properly with lastool.

So be prepared to message the data to get it formatted the way you need. GDAL is your friend in this case.

Cheers,

Mike

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[Möst, Karin (LDBV)]

Hi Mike,

 

thank  you, I did not have that information.

 

I finally managed to convert the  .gsb-file to gtx (using several software packages, so maybe the Geotiff format wouldn’t be a bad idea for a geoid)

Then I used lasvdatum and compared the results with the results of our software.

Except for +/-1 mm in East, North an Height they were identical (our software used so far changed  xy, too)

 

From now on we will use lasvdatum since it reduces processing time dramatically.

 

Thanks to all of you

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