Occassional thoughts about orienteering

Monday, June 18, 2012

Nice terrain in North Dakota


I spent some time exploring the terrain I wrote about last week and I was not disappointed.  The terrain is interesting and runnable (even with summer vegetation).

You can see a GoPro chest-cam video with a GPS track and map to get an idea of the area.

The map I'd created from lidar data and OL Laser turned out to be quite good.  The main changes that it would need to be a really good map would be adding slope tags to help an orienteer distinguish depressions from hills, add the small trails, improve the vegetation detail, and add the occasional fence lines and power lines.

It would be tedious, but not difficult, to add the slope lines based on the lidar data.

The vegetation could be improved by using green circles to indicate the distinct lone tress that show up in the current map and adding some distinct vegetation boundaries for the edges of the larger stands of trees.  I think I could do a pretty good job by comparing the lidar data to Google earth images.

Getting the small trails consistent and accurate would take a mix of studying air photos and spending some time in the terrain.

Getting the fence lines correct would take a visit to the terrain.  You might be able to get some of the fence and power lines sketched in from air photos.  The Bing Maps photo has a lot of detail.

It might be worth adding some marshy ground.  When I ran around the area I didn't get my feet wet, but I saw a couple of areas that looked like they'd be marshy during part of the year.

The biggest problem with the area is where it is - North Dakota.  As best I can tell there aren't any orienteering maps or orienteers in North Dakota.

Back to okansas.blogspot.com.

posted by Michael | 7:51 PM


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


Monday, June 11, 2012

A modest lidar-based orienteering training map


If you're interested in how lidar (aka laser scan) data can be used to generate orienteering maps, you need to be checking out what's going on over at RouteGadget.   

I don't have the computer skills to do as much, but I'm learning.  I spent some time this weekend looking at some very interesting terrain and creating a map with OL Laser.  I thought I'd share what I've been doing.

From the lidar data - which I was able to find and download for free - I generated 2.5 meter contours.  I also generated an "intensity" image based on the ground.  From the intensity image I was able to pick out roads, trails and parking areas.  I could also make out vegetation from the intensity image (which is something like a black and white photo).  But, I decided to use the vegetation data in the lidar to generate vegetation information.

To create a rough vegetation map, I used OL Laser's object height feature.  For anything below 0.8 meters, I created a light yellow shade.  For everything above 0.8 meters, I created white areas (to correspond to forested areas).  

You can see the results below.

I'm guessing the forest might be a little bit thick, so I also created a version where I shaded objects above 0.8 meters with light green.

You can see an air photo of the area below and see how it matches up.  To provide some context, the area shown is about 1.5 km from east to west.

I haven't been to this terrain.  It certainly looks very interesting.  I think it must be some sort of sand terrain.  I expect that I'll know more once I've had a chance to see it in person.

One thing I haven't done (and that's just because I've been lazy), is use the latest version of OL Laser.  I need to get my act together and download the latest version.

Back to okansas.blogspot.com.

posted by Michael | 8:21 PM


Saturday, June 09, 2012

Top 20 finishes at WOC 2011


What are the chances that an orienteer finishes in the top 20 at a World Champs for the first time?  How often do we see people having their first top-20 WOC finish?

I can't say why, but I wondered about that last night.  I took a look at the results of the middle and long distance WOC races from 2011.  For each of the runners in the top 20, I checked their WOC hsitory (via WorldofO) and checked the year that they first finished in the top 20 in an individual WOC race other than a sprint.

For example, Annika Billstam was in the top 20 in both the middle and long in 2011.  She first made a top 20 in 2009.  Lizzie Ingham finished in the top 20 in both the middle and the long in 2011.  Ingham had never run a WOC before.

The graphic below shows the results.  The darkest purple shade is for people who finished in the top 20 in 2011 who had never before finished in the top 20.  The lighter the shade of purple, the longer ago the person first made a top 20.  The blue-ish shades are for people who first made a top 20 a long time ago.  That brightest blue shade at 14th place in the men's long in 2011 is for Velentin Novikov.  Novikov had his first top 20 WOC result in 1997.

The pattern that jumps out is that a lot more women than men finished in the top 20 for their first time in 2011.

Note: I haven't done any "quality control" on either the data from WorldofO or my own data entry.  I've got at least one known typing error in my spreadsheet but it doesn't change the overall picture.

Back to okansas.blogspot.com.

posted by Michael | 9:44 AM


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