OpenTopography Blog

Information and discussion related to high-resolution LiDAR topography for the Earth sciences

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Category: TLS

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Filtering vegetation from Terrestrial Laser Scanning data using the Point2Grid tool

Posted on Fri, February 26, 2010 by ccrosby in Software • TLS

Max Wilkinson, a PhD student in the Dept. of Earth Sciences at Durham University in the UK, recently sent us a link to a video of a seminar he gave on methods of vegetation filtration from Terrestiral Laser Scanning (TLS) data using the Points2Grid tool developed by the OpenTopography team (originally developed with GEON funding).  Points2Grid is a Windows application that implements the exact same DEM generation algorithm that is used in the OpenTopography point cloud processing system.  It was developed to allow users to get the same DEM generation capabilities as are available in OpenTopography for non-hosted data. 

Dealing with vegetation in TLS scanner data can be a significant problem, and Max shows in the video how he is able to use the MIN surface feature in P2G to remove much of the vegetation from the scan.  Points2Grid is not technically designed to filter vegetation, but the minimum surface function can act as a low budget filter.  P2G is also handy for reducing the complexity of the point cloud data down to something more manageable for analysis.  In this case, Max has much higher shot densities than he needs to construct a surface from the data, and P2G helps to reduce the amount of data he is working with:

From the TLS perspective, I’m finding P2G is tremendously useful for distilling large pointsets down to a size whereby the computing time required to test various interpolation methods becomes bearable! I had previously spent many hours waiting to see the output of an interpolation based on millions of points, only to find the parameters I used were not quite right. With the reduced computing time I’m now able to run more interpolations in various programs with a range of different parameters to see the results. I’m now using arcGIS for interpolations of TLS data, rather than just goCAD. For example, I’ve just finished a flow routing analysis of footwall drainage in arcGIS. A big thank you to the team for making P2G available!

Screen capture of the video:

You can download the video from Max’s page here: Vegetation Removal.avi (124 MB download). 

I had difficulties getting the file to play in Quicktime on a Mac, but the video played perfectly in open source (free) VLC player.  You may also need this ffdshow codec provided by Max.

The GEON Points2Grid tool can be downloaded via the lidar.asu.edu site.  I recommend reading the P2G Instructions / Help doc and also looking at the this page on how the search radius parameter in P2G works.

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Close range morphological measurement for the earth sciences

Posted on Mon, December 08, 2008 by ccrosby in TLS

Here is an announcement related to terrestrial laser scanning that should be of interest to the OpenTopography community. The announcement came through on the GEOMOD-LIDAR-L listserv this morning:

Dear Colleagues,

ISPRS V/6: Close range morphological measurement for the earth sciences.

I’m pleased to announce the formation of an International Society for Photogrammetry and Remote Sensing (ISPRS) working group (V6) to promote and coordinate the use of modern geomatic techniques (terrestrial laser scanning and close range digital photogrammetry) for the measurement of natural objects. This should be of interest to a wide spectrum of researchers involved in 3D reconstruction, modelling and quantitative earth science research. The following fields are just an example of those within the broader earth science discipline: geomorphology, geology, glaciology, hydrology, agriculture, forestry, surface roughness and climate change studies.

For further details see: http://civil-unrest.lboro.ac.uk/isprsV6/index.html

or contact either myself, Jim Chandler j.h.chandler@lboro.ac.uk (Chair), or Rene Wackrow r.wackrow@lboro.ac.uk (secretary). Please note that involvement/membership is free and open to all: http://civil-unrest.lboro.ac.uk/isprsV6/becomeamember.html

Please circulate this announcement to colleagues who may be interested, and apologies for any cross-posting.

Best regards,

Simon Buckley
Co-chair, ISPRS Working Group V/6

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Airborne and terrestrial LiDAR coordination for The Great Southern California ShakeOut

Posted on Thu, November 13, 2008 by ccrosby in News • TLS

Today at 10 am The Great Southern California ShakeOut staged an Mw=7.8 earthquake on the southern San Andreas Fault to raise public awareness of earthquake hazards and to allow public responders and the scientific community to practice their response to such an event.  As part of the scientific response, UNAVCO is coordinating community equipment deployment and data acquisition activities via their Great Southern California ShakeOut Response discussion forum.  A sub-forum, coordinated by David Phillips, is tracking the airborne and terrestrial LiDAR response to the earthquake.  As of 12:23 pm (CA time), TLS resources from University of New Mexico LiDAR Lab and NCALM are availble to respond to the event.  NCALM and UT Austin Center for Space Research have also confirmed that they could respond with airborne scanners and aircraft.

LiDAR acquisition immediately following a large, ground-rupturing earthquake on the San Andreas system, will be of great importance to preserve slip distribution, offset features and to provide a post-earthquake snap-shot of the landscape that could then be differenced with the recently acquired B4 or GeoEarthScope LiDAR topography datasets to provide information about near-field deformation along the fault rupture.

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