Occassional thoughts about orienteering

Sunday, October 10, 2010

Enough to get started with Lidar?


OL Laser is a program for creating orienteering basemaps from lidar (aka laser scan) data. I'm far from an expert on either lidar or OL Laser, but I've been playing around with the program and thought I'd write up some notes.

I'm impressed with OL Laser and have found it easy to use. I'm sure I've just scratched the surface of what it can be used for. I'm far from being an experienced user.

OL laser is useful...but it is written in Swedish. I thought I'd translate bits of the main screen. With the translation and a willingness to experiment (and a bit of lidar data), I think you'll be able to get started even if you don't understand Swedish.

You can download OL Laser (click on the "ladda ner" link)

Below is the main screen and translations of some of the items on that screen.

The first three buttons are for opening the data:

Oppna laserdatafil = open the laser data file
Spara laserdatafil = save the laser data file
Filinfo = file information

The next two buttons are for creating the "GRID or TIN" (a Google search for "lidar and GRID" and "lidar and TIN" should explain the terms):

Skapa GRID/TIN = create the GRID/TIN
Installningar = settings

Next are two blocks of buttons. One is for contours (hojdkurvor) and the other is for images (bilder). I'm going to focus on the image items first:

The drop down menu labelled "valj typ av bild" means "select the type of image." There are four options:

Laserpunkklass = laser point category
Intensitet = intensity
Lutning = slope
Terrangskuggning = terrain shading

You'll see three buttons below the drop down menu:

Installningar = settings
Skapa bild = create image
Spara bild = save image

I'm just going to skip over the "hojdkurvor" (i.e. contours) menu and go to the final set of buttons labeled "rita" (i.e. draw). You'll see two boxes you can check:

Rita ut kurvor = draw contours
Rita ut bild = draw image
Installningar = settings

That's just barely enough translation that you ought to be able to begin to play around with the program.

I'll walk through an example:

The first thing you need is some data. If you've got some data, great. If not, you can find some online. One source is the Kansas Data Access and Support Center's collection of lidar. The data are free to download, though you have to register. The most interesting data are the "all returns" files.

Once you've got some data, you can open it in OL Laser (use the button at the top of the program screen labeled "oppna laserdatafil"

Next, you'll move to the GRID/TIN section of the menu. First, click on the "installningar" (i.e. settings). A new menu opens. Now you've got lots of options and lots of info. It is useful to understand Swedish at this point. I'm not going to translate all the terms. Instead, I'll describe the easiest thing to do to start playing with the data.

Look for the checkboxes under "klassificering" (i.e. classification). Make sure the box labeled "mark" (i.e. ground) is checked.

Look for the button/boxes just below under "returnummer" (i.e. return number). Make sure "sistareturnen (mark)" is checked.

At this point, you've opened the data file and told the program that you're going to create a GRID of the ground.

Go back to the main menu and click on "skapa GRID/TIN." It should take a few seconds to create the GRID.

At this point, you don't have anything to look at.

Go to the "bild" (i.e. image) set of items and select the type of image from the drop down menu. "Terrangskuggning" is a good first choice. Don't worry about the "installningar" just click on "skapa bild." It takes a few seconds to create the image.

At this point, you still don't have anything to look at.

Go to the "Rita" section of the main menu and click in the box labeled "rita ut bild" (i.e. draw the image) and you should get an image.

That's a quick - and rough - intro to OL Laser. You can start to play round with different images and different settings.

I've written about my various experiments with lidar. I'm very much self-taught. I'm far from being an expert. I don't really understand all of the technical details of how lidar works or of how best to use the data. But, I've learned enough that I can use the data to generate a useful basemap.

Back to okansas.blogspot.com.

posted by Michael | 4:18 PM


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