Block Adjustment

[Kayla]

I am looking at two sets of Lidar that need to be compared to give a the change between years; however the lidar are offset.
I would like to do a block adjustment so the lidar aligns properly, however I am unsure what lastool will allow me to accomplish this.  
I have previously viewed this data in micro bentley station and have attached an image showing the offset of my lidar.

[Jonah Sullivan]

There are two situations I can think of:

1) there is a constant vertical offset between the two point clouds (block shift)

2) there is a variable vertical offset between the two point clouds (fitting clouds together)

For either situation "lasheight.exe" can be used to apply a vertical offset.

For situation 1 a XYZ point file (any resolution) with Z values equal to the vertical offset can be used with the -ground_points and -replace_z keywords to reduce the point cloud to the correct elevation.

For situation 2 a XYZ point file (regular grid with high resolution such as 1 metre or less) can be created by deriving a DEM from each point cloud and then subtracting one from the other. The resulting ESRI ASCII grid (ASC or XYZ or LAS or SHP) can be used with the -ground_points and -replace_z keywords to reduce the point cloud to the correct elevation.

Jonah Sullivan 
Geospatial Analyst

National Topography Services  |  National Location Information Group

Environmental Geoscience Division  |  GEOSCIENCE AUSTRALIA

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GPO Box 378 Canberra ACT 2601 Australia

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[Łukasz Ewertowski]

Hi,

You can try to use CloudCompare http://www.danielgm.net/cc/  to align two point clouds. There is functionality to automatically align point clouds.

If you do not succeed you can contact me, i can help you.

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[DJ Lehto]

Looking at the screengrab.  I see potentially one of two problems.  First it could be a height of instrument error, possible one set was processed where the basestation height was not subtracted or added twice.  Secondly the problem could be related to a geoid issue.  Whereas it wasn’t applied or double applied.  Since you have tscan loaded in your screenshot and if you are confident that the data seems to be a straight vertical shift of “X” units.  There is the tool called transform points under the tools menu on the tscan point window that allows you to modify the elevation (DZ) by subtracting or adding the difference.  When you do that make sure you only load the data you wish to change to the elevation you want (Don’t have both sets loaded).

 

D.J. Lehto | Production Manager

GeoDigital International Inc.

1 Antares Drive, Suite 140 | Ottawa, ON | Canada K2E 8C4

tel: 613-820-4545 x 286 | cell:  613-668-8522

fax: 613-820-9772 | toll free: 1-800-231-4969

website: www.geodigital.com

 

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