Occassional thoughts about orienteering

Wednesday, June 13, 2012

More fun with lidar and vegetation


Lidar data includes information on "density" of objects.  While I'm not exactly sure what that means, I think it gives information that can help understand how thick a forested area might be.  The map below shows an image where I've used different shades of green to identify regions of different object density.  The darkest green areas are areas of higher object density.  The white areas are areas of the lowest density.

To get this image, I used OL Laser to assign the shades to different object densities and I excluded any points that were within one meter of the ground.

My previous experiments with trying to map runnability were based on object heights.  Those experiments were moderately successful.  I was able to use the information to help understand runnability.  But I still had to do a lot of interpretation in the field and make a lot of changes.  I'm hoping that the density information will be more precise, requiring fewer changes.

I'm looking forward to comparing the map above with the actual terrain and see how well the density data maps vegetation.

Back to okansas.blogspot.com.

posted by Michael | 8:53 PM


I want to check out if the vertical vegetation density profile will correlate better with actual runability.

I.e. not just the maximum canopy height but the profile/distribution of intermediate returns.

I have a large test area that's intended for the 2015 JWOC that we hope to host in Telemark, Norway.

Parts of the area have recently updated current maps, so I do have something to calibrate against before going out in the forest to field-check.

The maps I posted on June 11 are based on canopy height and they do a good job of showing the mix of open and wooded areas. You can see how well they match the photo. I think the object density information looks like it has the possibility of providing a good look at the runnability of the forested areas. I'm looking forward to checking out the terrain and seeing how well the data showed changes within the forest.

Just like you I have used canopy height up to now, the problem is the huge difference between high canopy forest which suffocates anything below it, leaving a very runnable area, vs another patch with the same top heights, but which also has significant intermediate returns in the most interesting 1-3 meter range.

Due to the top cover, the density of the low/brush returns will be much lower than in an area of pure brush, but the runnability might be very similar or even worse.
I spent a little bit of time in the terrain yesterday. I looked at some of the vegetation differences that show up in the image in the map in the blog post. I spotted some of the differences, but they didn't really reflect differences in runnability so much as differences in how the trees looked. Part of the issue is that the forested terrain in this area is almost all very nice and open. Part of the issue is that I haven't figured out the ideal way of pulling the useful information from the lidar.

I plan to keep experimenting with the data and see if I can find something a little more useful.

I think getting useful runnability information from the data is going to be tricky.

I think that the density information will prove more useful than the height information. But it is going to take some more practice to figure out the best solution.

I will keep trying!

Shorter is usually much better. It is much simpler to grow to be entangled in grammatical nuances the lengthier the sentence grows. Keep sentences quick, descriptive and logically flowing from 1 to the next. If you like to create extended sentences, go by means of http://www.procustomwriting.com and break them up- typically at the factors exactly where clauses begin and stop (locations in which you would place a comma or a semicolon, you can rather put a time period and make a new sentence!).
Post a Comment
March 2002April 2002May 2002June 2002July 2002August 2002September 2002October 2002November 2002December 2002January 2003February 2003March 2003April 2003May 2003June 2003July 2003August 2003September 2003October 2003November 2003December 2003January 2004February 2004March 2004April 2004May 2004June 2004July 2004August 2004September 2004October 2004November 2004December 2004January 2005February 2005March 2005April 2005May 2005June 2005July 2005August 2005September 2005October 2005November 2005December 2005January 2006February 2006March 2006April 2006May 2006June 2006July 2006August 2006September 2006October 2006November 2006December 2006January 2007February 2007March 2007April 2007May 2007June 2007July 2007August 2007September 2007October 2007November 2007December 2007January 2008February 2008March 2008April 2008May 2008June 2008July 2008August 2008September 2008October 2008November 2008December 2008January 2009February 2009March 2009April 2009May 2009June 2009July 2009August 2009September 2009October 2009November 2009December 2009January 2010February 2010March 2010April 2010May 2010June 2010July 2010August 2010September 2010October 2010November 2010December 2010January 2011February 2011March 2011April 2011May 2011June 2011July 2011August 2011September 2011October 2011November 2011December 2011January 2012February 2012March 2012April 2012May 2012June 2012July 2012August 2012September 2012October 2012November 2012December 2012January 2013March 2013April 2013May 2013July 2013September 2013