Sign in to follow this  
Guest sgtschmitz

How to determine LOD and CDED

Recommended Posts

After about 2 months of trying to figure out how to create mesh from the CDED1(1:50,000)files, I finally got it, and the results are outstanding. Before I post them to the file library, I would like to be able to determine the LOD of the files. In my .inf file I am using LOD = Auto, so I can't or don't know how determine it. The CDED1 files are anywhere from .75 arcseconds to 3 arcseconds. I am using Erdas Imagine 8.6 to import and merge them into a geotiff, Microdem 7. something to convert them into a .bsq file and then "resample.exe" to convert to a .bgl file. I am subsetting and naming the files based on the NTS (National Topographic System)1:250,000 scheme, so for the most part this involves 32 CDED1 files that have to be processed. (ie, 92h, 92g, etc) These are 2 deg by 1 deg cells. The file sizes are quite large, anywhere between 20 to 27 megs so far. Today I did 5 of the cells and it takes me about 45 mins to perfrom the required operations to get it to the .bgl stage not including the download time for the files. Even though not all of the CDED1 data is available, the merge function in Erdas Imagine allows for the overlaying of the more accurate data on top of the 1:250,000 data which is really handy. Now that I know the process, I can make just about any mesh as long as I can get the data. So, as I said earlier in this post, if anyone knows how to determine the LOD of a .bgl file, it would be most appreciated.P.S. I have already done 92g, 92h, 82e, 92k, 92i and a couple smaller areas in the BC area.

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Hi there:well, that does sound like you've got quite the operation going there - good stuff!I'd recommend setting the LOD yourself. If you look at 1:50,000 CDED1 Table in GeoBase_product_specs_CDED1.pdf (page 2) you'll notice that all areas south of N68 are compiled in 0.75 arcsec, i.e., all of B.C. has the same resolution. I'm not sure which LOD the AUTO setting would pick (you can "measure" this in TMFViewer by zooming all the way in and checking the distance between two adjacent cells) but your file sizes suggest LOD11.I recommend setting LOD to 10 or even 9. Compiling at LOD11 will make visible some of the errors and artifacts, results in huge files, and has a smaller visibility radius, relative to LOD10 or LOD9. For my CDED1 meshes I have used LOD10 in the southern parts of B.C. and LOD9 in the areas with more gentle topography. I've posted a few comparison screenshots at the end of the "mesh settings" gallery: http://portal.fsgenesis.net/modules.php?se...=view_album.phpOne thing to look out for, and you probably know this, is that the files need to be compiled to fit the LOD grid. If you compile the 32 files of each 250k map sheet area without adding "buffer" zones along the edges, you'll end up with gaps between the compiled sheets. Again, TMFViewer is the tool to check for problems in this regard.Hope this helps. Good luck. Cheers,Holger

Share this post


Link to post
Share on other sites

Excellent advice. I am now creating the mesh tiles at LOD = 10. When I looked at the files in TMFViewer, I did have gaps between the tiles. So ,in Erdas Imagine I added the surrounding CDED1 and clipped each edge to +.075 of a degree from the normal 1:250,000 size and this seems to have solved the problem. I am getting a bit of an overlap north to south, but I don't think that effects anything. And the file sizes are not around 7 megs. It now takes me about about 1 1/2 hours to do a 1:250,000 sheet. I've looked at your comparison shots in the link that you sent and I really like the LANDSAT imagery over the default imagery. So that's my next project. Eventually, I would like to get into the Landclass stuff and see if I can use ESRI shapefiles to improve on the default landclass.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this