Getting started with the Fusion program and LiDAR data

[Steve Galehouse]

ENTS-

At Ed's suggestion I'm posting this simplified tutorial for using the Fusion program and LiDAR data. The tutorial provided Fusion is quite complex and perhaps more in depth than the way most ENTS would utilize the program, so this sort of a "quick and dirty" way to become familiar with Fusion. The data source I've used is from Ohio, but the information should be adequate to get one familiar with the program and what it can do, and then you can search for data in your home state:

1). Download and install Fusion from: http://www.fs.fed.us/eng/rsac/fusion/

2). Go to this site to download Ohio data:http://gis4.oit.ohio.gov/osiptiledownloads/default.aspx . Zoom in on an area until tile numbers and boundaries are visible---a tile will have a number like N2215545(tiles in the southern half of the state begin with S. Use the "select" option, icon at the upper right of the map, to grab the number. When you select a tile, five file options will show in the box to the right of the map. Download the TIFF file, the LiDAR file, and the ASCII file. Disregard the other two. Once downloaded, extract/open each file and move contents to a folder of your choice(I create a folder with the site name and leave on the desktop for convenience).

3). Open Fusion, then:
    A). On the options bar to the left of the Fusion screen, click on "Image"; a box prompting you to open a file will appear, select the folder you've put the extracted file in, and an image(.tiff) file will be there--open that file to load into Fusion. An aerial photo should then appear in the Fusion screen.
    B). Next, on the  options bar to the left, click on "Raw data".An "open" prompting box will appear again, with LiDAR, .lda or .lds as the file type. Click on the file in the box, then "Open". Another box will pop up; just click "OK"(not "add file").
    C). This is the only tricky part. At the top of the Fusion screen, in the toolbar, select "Tools", then "Terrain model", then, "Import ERSI ASCII raster files". An "Open" prompting box will appear again, but with no files visible. Change the "File types" from "ERSI ASCII raster files(*.asc) to "All files"(just click the down arrow to the right of the file type pane). Now all the files loaded into the folder will appear. You are looking for a text file about 30.5 megabites in size, usually in the second position down from the .tiff file. Click on this file to open; another box will appear: "Import ASCII raster terrain model"---Click "Import" at the bottom left of this box, wait a bit, and when a file directory appears in the pane above the import button, just close the box.
    D). Click on the "Bare earth" button on the left bar of the Fusion screen---an "Open" box with a .dtm file will appear(this is what was just created by the process in "C". Click on this file, a box titled "Surface model" will appear, click "OK", then elevation lines will appear on the aerial image. You are now ready to view the data.

4). Highlight an area with the cursor, wait a bit, and the "LDV" window will appear with tree heights color coded as per the height scale to the left of the viewer screen. Left click and hold to rotate the view, use the wheel to zoom in/out, right click for many other options(the "surface" option is very useful, as in the "marker" option to adjust point size. Once you get to this point, it's just a matter of playing around and getting familiar with the graphics functions of the program. Before you close the program, click the "save as" to store the data to a name.

The process sounds complex, but once you've done it a few times, it's a snap.

[AndrewJoslin]

Thanks for posting that Steve, I've been wanting to explore LiDAR but got bogged down trying to figure it all out.So far I haven't been able to find much data for Massachusetts but I may be looking in the wrong places.
-AJ

[edfrank]

ENTS,

Following my own advice, this is a letter sent to me by Paul Jost concerning LIDAR data for Pa.  I am posting it so that it can[googlevideo][/googlevideo] be of service to others also,  As a additional note the example files in the LIDAR tutorial consite of two files each just ove 100 MB in size, so downloads on dial-up for the tutorial will be extremely long.

Ed

Ed,

Just in case you don't have the links required to work with Pennsylvania LIDAR:

The best place to get LIDAR data for Pennsylvania and most states that have it available is:
http://lidar.cr.usgs.gov/LIDAR_Viewer/

The imagery to go with it is located at:
http://www.pamap.info
http://www.pasda.psu.edu/uci/SearchPage.aspx
http://maps.pasda.psu.edu/website/Image ... ools=PAMAP

The software to view LIDAR is at:
http://forsys.cfr.washington.edu/fusion ... atest.html
and the tutorial is located at:
http://www.fs.fed.us/eng/rsac/fusion/

Obviously, it's accuracy is best on flatter land and on trees not directly over water.  Accuracy over slopes is minimized along the flight lines and becomes worse as the scan angle gets away from true vertical where the laser is scanning off to the side of the plane.  Where the two errors combine, hillsides can be seen with unusually large numbers of trees that may appear excessively tall while similar sloped nearby hillsides of similar forests will show few if any tall trees.  Knowing it's limitations can help one to interpret the data and make judgments to prioritize ground truthing hikes.  

Paul

.

[Joe]

For those of us totally unfamiliar with LiDAR, how about a 1 paragraph explanation of what it is and what Fusion is?

And, how does it compare with stereo photography?
Joe

[edfrank]

Joe,

Fusion is simply a viewer for LIDAR data.  It is a 3-d representation of a topographic surface that can be rotated and viewed from different angles.  It consists of a ground layer and a layer representing the tops of trees.  The height between the two surface is color coded.  Steve Hallow used two different representations of the data from Ryerson SP in a post yesterday - one from overhead and one from the side:  viewtopic.php?f=154&t=2256  




The orangish color represents the tallest trees - sycamores found in the valley bottom.

Ed

[Steve Galehouse]

Joe-

As Ed said, Fusion is a program that uses LiDAR(Light Detection And Ranging) data to measure and visually represent canopy height compared with ground elevation. The canopy height range of a sample is color coded, with the actual height measurements given on the left side of the LiDAR Viewer screen. Samples can be manipulated by rotation and color settings, as well as other ways. I've never used stereo photography, but I don't think stereo photography can give actual height values, although one could probably get some idea of species composition, which Fusion and LiDAR cannot provide. The utility of Fusion for me is locating trees and then examining the terrain( minus the canopy data) where the trees are found---this makes the trees very easy to find on foot. I've attached three pics---the first a LiDAR tile in the Fusion program, with the sample area highlighted lower left, the second an image of the sample area in the LiDAR Viewer showing color coded tree heights, with the tallest at 166.57', and the third showing the sample area terrain view.

               

                       

                                       

               

               

                       

                                       

               

               

                       

                                       

               

Steve

[Joe]

so, how accurate is it?
Joe

[Steve Galehouse]

so, how accurate is it?
Joe

I've found it to be extremely accurate, with the tallest trees always found where the LiDAR data indicates. In the example I gave above, the tallest tree in the sample was 166.57', which Rand Brown and I measured with laser rangefinder and clinometer to 163.72'. In another sample a 161.37' LiDAR hit measured to 160.8' with laser/clinometer. I could give many other examples, but I don't think the accuracy of LiDAR data is suspect.

Steve

[dbhguru]

Steve,

   Thanks very much for doing this. I look forward to going through the process. I see it as growing importance to our shared measurement mission. As of this moment, I'm neck deep in formulas and processes from Michael Taylor on this Triangle Method and its adaptation to the equipment configuration that I have, which is not small order. When I'm able to come up for air, I'll dive into LIDAR and also produce the tuliptree map I promised. There is a lot that is exciting going on. Ed's reorganization of the BBS interface has come at a good time.

Bob

[Joe]

Steve,

   Thanks very much for doing this. I look forward to going through the process. I see it as growing importance to our shared measurement mission. As of this moment, I'm neck deep in formulas and processes from Michael Taylor on this Triangle Method and its adaptation to the equipment configuration that I have, which is not small order. When I'm able to come up for air, I'll dive into LIDAR and also produce the tuliptree map I promised. There is a lot that is exciting going on. Ed's reorganization of the BBS interface has come at a good time.

Bob

Wow, since LiDAR is that accurate- I should think it would be worth the trouble to systematically review ALL the LiDAR stuff available- both for public and private lands. If on private land, the owner could be contacted with a note like, "Respecting your private property rights, I have examined this publicly available information and I have reason to believe your property may contain some exceptionally large trees that may be of scientific interest". Such a note might prove fruitful. Otherwise, most owners really don't like tresspassers. Think of all the tens of millions of acres of private land out there.

When I stop being so lazy, I'll have to look at LiDAR. It may be perfect for big tree work, but I think old fashioned stereo photos may be better for routine forestry work- in so far as getting a good sense of the overall lay of the land and relative heights of trees, for stand analysis.
Joe