OCAD and Lidar

What you can do with LIDAR data in OCAD and how to get it.

This presentation will show, step by step, how to take Lidar data and put it into OCAD 12 to produce a basemap for field work. It also shows what Lidar can give you to work with. This is specific to OCAD 12 although it may work with OCAD 11 that allows import of .las files. If you don’t have these programs, you can still see what you get with the LIDAR which may make you take the plunge to get it.

It is assumed that the .las files have been obtained prior to starting this process. Other files can be imported, too; see list in top right. If you have Lidar processed by a program like Karttapulluatin, then you can skip past the download part to see what the Lidar can do for you. Page 3--get Lidar files; Page 4--start using them in OCAD.

Starting the Process

Getting Lidar Files

Getting Lidar files may be very easy or it may seem convoluted. The Lidar .las files that can be processed by OCAD may be stored differently by the various states.

For example, the process to obtain files from New Hampshire is different from the way you get files from New York. I have gotten files from both New York and New Hampshire. They both have their quirks but it is possible to do.

Perhaps the easiest way to get the files the first time is to ask someone who has obtained them. In New Hampshire, where I live, some things don’t make much sense in that the files seem to be organized according to the watersheds of the state but my town, Wolfeboro, is cataloged in the Connecticut River watershed -- odd, because there are a few river systems between here and there. As I said, ask someone who has done it unless you can figure it out yourself.

The best way to locate the files is by searching for “lidar files (your state)”.

Most files will come as a ZIP file. Most likely, your computer can unzip them. One issue is that it might come as a ZIP64 file. It may be that you can just change the file to a ZIP file by renaming it after you erase the “64”. Ask for help if you need it.

It is probably a good idea to now save your file with a name of the map that you are creating. File > Save as...

Then click on the DEM menu at the top of the page.

Next, click on the DEM Import Wizard and you will get the following screen.

Here, you will click “add” and then browse to and select the .las files that you want to process. It is possible to process more than one .las file at a time but it will take longer and requires more memory. OCAD may also get cranky if you open or close or do much of anything with your computer while it is processing the data and it may become unresponsive. If this happens, you may have to shut down OCAD with ctrl/alt/del and then restart the process.

On this screen you may also need to do a few more things…

Some .las files seem to be in meters while others seem to be in feet. Data from a given State resource are probably all in the same units. In New Hampshire, the data are in feet. For that reason, the box “Convert height values from feet to meters” should be checked. If you are only interested in a portion of the area in the .las file you may want to deal with the “extent” but it probably isn’t worth worrying about. When ready, click “Next”. Now, you need to figure if you need to change the data to meters from feet. You can do this by trial and error (analyze the data and then check with a USGA map) or follow the directions in the next slide.

The next screen gives information about the .las file or “tile” that you are working with and indicates what you are going to create. All of these files that are checked are useful for some purposes so just click “Next”.

Again, the next screen indicates what you are going to get as an output. All of this output is useful so you should click “Next”.

On this next screen, you specify what contour lines you want to have on your map. It is also used to set the OCAD symbol for each line level. On the example screen below, the 1 meter interval line will be represented as form lines, 5 meter contours are contour lines, and 25 meter lines are index contours.

You can change these values to your liking. On some maps, .5 meter lines may be helpful but on other maps, there may be way too much “noise” to make it useful. The contour interval can be .1, .25, .5, 1, 2, 2.5, 3 and 4 meters. You have lots of choices… You can try processing it with

different intervals but start with the ones shown.

The next screen just deals with the colors that you will see in the product. Most likely, the one that is the default will be the best for you but you can experiment if you wish. You do want to “Load exported map as a background map" and this is the default.

The defaults seem to work relatively well. Adding the “oblique light shading" may help a bit in some circumstances. The important thing here to make note of is the “exaggeration” that by default is “4”. This is fine to start with and you can later increase this value, when you are working with your map after the data has been processed, to “10” which may help you see things better on the map.The azimuth and declination can be left at the default. Once the data are processed, you can rotate the map so that magnetic north is at the top of the map. This is done by going to the Map Menu, then Transform, then Rotate. Put in the appropriate value to get to magnetic north in your area.

The next two screens deal with slope gradient and vegetation height. Leaving these at the defaults is probably best.

At the same time, it may be that for the particular area that you are mapping, adjusting the “Classes” of vegetative coloring is helpful.

Lidar looks at first reflection (vegetation tops) and last reflection (ground) and then colors these according to the color you choose. If you click on the “2.00 - 12.00 m” youwill see that this is “green” instead of with “no color”. The different colors allow you to see what kind of vegetation you have in the forest. Normal forest has tall trees and “no color,” while shrubs or grasslandshave other colors on the resulting screens that will be developed.

After clicking “Next,” a data analysis process starts. After a short time another little screen shows up. It is generally best to accept the default. Some people may want to adjust the map to magnetic north here but it is probably better to do this at a later date because most other file imports (such as aerial photos, etc.) to be processed will be to true north. Clicking OK initiates the process of producing contours and the background views.