Transform Point Cloud elevations
AndrewW
Global Mapper UserTrusted User
Hi,
Is there any way of transforming elevations of point clouds eg las or xyz file by:
Andrew
Is there any way of transforming elevations of point clouds eg las or xyz file by:
- A fixed amount ie a z offset.
- Via a z transformation grid like a conversion from Ellipsoid to an Orthometric heights.
Andrew
Comments
-
Andrew,
You could export the point cloud to a Simple ASCII Text File and use the Point Offset/Scale tab of the export dialog to scale/offset the values, then load that back in and export to a new LAS vector point cloud file.
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
Hi Mike,
Ok that solves issue 1. Thanks.
Issue 2 is more of a problem. I can get a result on a surface by converting the z transformation grid to a surface and can then add it to another surface but it doesn't work on point clouds because I loose all the las point attributes. My Z tranformation grid is a grid of coordinates with each point being the z offset. -
Hi Mike,
I have another problem with process.
My input data looks like this:
1448177.830 5128077.260 460.240 10
1448177.950 5128077.280 460.220 12
1448178.060 5128077.310 460.240 11
1448178.180 5128077.330 460.130 12
I wrote a script to export as simple ascii which includes:
EXPORT_VECTOR FILENAME="%DIR%%FNAME_WO_EXT%NZGD09.asc" TYPE=SIMPLE_ASCII FEATURE_SEP=NONE EXPORT_ATTRS=NO_STYLE COORD_OFFSET=0,0,0.47 EXPORT_ELEV=No
and the result is:
NONEDESCRIPTION=Unknown Point Feature
NAME=10
INTENSITY=10
ELEVATION=460.24
1448177.830,5128077.260,459.77
NONEDESCRIPTION=Unknown Point Feature
NAME=12
INTENSITY=12
ELEVATION=460.22
1448177.950,5128077.280,459.75
How do I get the data back to a single line of text for each record ie xyzi -
I have a solution if you have the grid of values to add to the elevation of each point. After you load the initial point cloud, select all of the points and edit them and rename the ELEVATION attribute to something else, like Z_ORIG. Then right-click with the Digitizer Tool and select to get elevations from the grid data for the selected features. This should add a new ELEVATION attribute to the points from the grid. Then, right-click on the point cloud layer in the Control Center and select to CALC ATTR and update the existing ELEVATION attribute by adding the Z_ORIG attribute to it. This should make your ELEVATION attribute now adjusted from the grid and you can then export to a new LAS vector file and keep all other original attributes.
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
Works a treat.
Thanks Mike -
It appears this is almost exactly what we've been trying to accomplish, but it doesn't seem to be working quite right. I notice in the data presented above the ELEVATION attribute and the z-value don't match. This is the problem we've been encountering.
I can get the z-value to "adjust" when exporting to a text file but can't get the ELEVATION attribute to change.
How can we keep the attribute and the z-value in sync? Or, alternatively, get the attribute to change since I can get the z-value to not export with the EXPORT_ELEV=NO option.
Thanks
Jay -
Jay,
What attribute do you have set as the 'elevation' attribute for the layer on the Control Center options dialog for the layer? This is where the Z value in a 3D text export would come from. Once you assign the elevation to come from a particular attribute then an attribute named 'ELEVATION' is not special anymore, it's just another attribute. The elevation will just come from there by default (as well as a bunch of other supported names) if you don't explicitly set an elevation attribute to use.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
Mike,
It's set to default. And it's the mis-match between the elevation and the z that's giving us the problem.
Jay -
Jay,
Which one is the actual elevation? I would just delete the other attribute. If you have multiple attribute names that are default elevation attributes, you simply get the first one that is in the list of built-in elevations treated as the elevation value. ELEVATION is before Z in the list so ELEVATION would be used as the elevation unless you explicitly set it to come from Z.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
Mike,
We're starting with the lidar las file, exporting to the ascii xyz with vertical adjustment and getting the following in the text output:
DESCRIPTION=LIDAR, Ground Shot
ELEVATION=135.69
CLASS=2 (Ground)
INTENSITY=72
SCAN_ANGLE=-5.0
RETURN_CNT=1
GPS_TIME=496496.1
POINT_SYMBOL=Elevation Shaded
4144009.02,13547616.81,83.19
DESCRIPTION=LIDAR, Ground Shot
ELEVATION=135.63
CLASS=2 (Ground)
INTENSITY=50
SCAN_ANGLE=-5.0
RETURN_CNT=1
GPS_TIME=496496.2
POINT_SYMBOL=Elevation Shaded
4144005.56,13547621.14,83.13
I can't figure out how to either get elevation not to export or to "recompute" to match the z value.
Can I just set elev_field=z on txt file reimport?
Jay -
Mike,
Actually I'm probably chasing the wrong issue(s).
Can we just get a Z adjustment (to elevation attributes and z values) when exporting to lidar las?
Jay -
Jay,
Ah I see what is going on. Rather than doing the Z adjustment on export and creating a 3D file, instead right-click on the layer in the Control Center and select the CALC ATTR option and adjust the ELEVATION attribute directly. That way you don't have a special adjusted Z value in the file and the original unmodified text attribute ELEVATION. The values would match.
I also updated the generic ASCII text file importer to override the ELEVATION attribute on import with the Z value specified so they will be consistent on import. I have placed a new build at http://www.globalmapper.com/global_mapper13.zip with the latest changes for you to try. Simply download that file and extract the contents into your existing v13.xx installation folder to give it a try. If you are using the 64-bit v13 version there is a new build at http://www.globalmapper.com/global_mapper13_64bit.zip .
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
Tom points out that calc-attr would be perfect if available in scripting.
Thanks
Jay -
Mike,
That should solve the issue. Unfortunately our attempts so far have indicated that using this method in a script is wayyyyyy tooooo slow. The ascii export and import takes an inordinate amount of time. We can manually use the calc-attr function and do several by hand in the time the script takes.
It will be great when you get calc attrribute into the scripting.
Thanks
Jay -
Jay,
I have also added support for the COORD_OFFSET and COORD_SCALE parameters for the EXPORT_VECTOR script command when exporting Lidar LAS files so you can do the offset and scale directly there too if you want.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
Forgot the link... I have placed a new build at http://www.globalmapper.com/global_mapper13.zip with the latest changes for you to try. Simply download that file and extract the contents into your existing v13.xx installation folder to give it a try. If you are using the 64-bit v13 version there is a new build at http://www.globalmapper.com/global_mapper13_64bit.zip .
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
Mike,
Assuming that will work as usual for your fixes......fantastic.
We were looking at days to run the original script.
Should be a few hours now.
Jay
Categories
- 12.7K All Categories
- 5.6K Features Discussion
- 342 Downloading Imagery
- 1.3K Elevation Data
- 380 Georeferencing Imagery Discussion
- 628 GM Script Language
- 53 User Scripts
- 113 GPS Features
- 414 Projection Questions
- 819 Raster Data
- 1.3K Vector Data
- 6.6K Support
- 177 Announcement and News
- 908 Bug Report
- 558 SDK
- 1.2K Suggestion Box
- 3.7K Technical Support
- 562 Other Discussion
- 129 GIS Data Sources
- 27 Global Mapper Showcase
- 233 How I use Global Mapper
- 107 Global Mapper Forum Website