Thursday, September 13, 2012

Mobile LiDAR Point Density - Part 2

I've had a brief hiatus from the blogosphere while working on a project that kept me out of town for a few weeks.  I usually do not travel with the system since our collection team is quite capable of anything I throw at them quite honestly.  However, the most recent mobilization was truly unique as you'll come to find out in future posts - can't share too much, yet.

Gene Roe, Managing Editor of LiDAR News, was successful in getting another article from me for the regular newsletter.  My latest contribution is a continuation of a previous topic and is titled:  Mobile LiDAR Point Density - Part 2.  I discuss how the following variables influence density:
  • Vehicle speed, measurement frequency, and scanner rates;
  • Angle of incidence and the impact of flat surfaces;
  • Distance to target and effect of rotated sensors; and
  • Collection paths and moving obstructions.
The images from the article are provided for a little more clarity. 

The image represents 3 passes along the same stretch of a 2 lane residential road. The data was collected at 25 mph with a scanner rate of 120 Hz. The three images show results of collecting at laser frequencies of 75 kHz, 100 kHz and 200 kHz – from left to right.
Using the vehicle speed and scanner rate, we can calculate the line spacing - the distance between lines of LiDAR points laid down on the surface.

The image above shows the data captured from one sensor along the centerline of a runway.  The data tapers off rapidly due to the limited backscatter caused by the flat surface. The point density on the pavement stripes at the extents is increased to to the material.

I will have one last article in the series next month.  It will focus on the resolution required to identify objects and tools that are available for feature extraction which utilize photography.

Feel free to leave a comment if there's a topic you would like to read about.


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