FYI ReDEM users

[bnsfsubdivision]

tried several times but with no luck, can one of you try and get the section i want for me so i can get started? ive decided since i cant get any canadian dem im going to just make a freelanced route using dem along with making my large switching route.

Sure just sent me the coordinates

[PapaXpress]

OK, using the 24K tile system I am finding that some areas offer 1/9 while others do not. My past experience is that mixing 1/3 with 1/9 doesn't work. Is this true?

[bnsfsubdivision]

ReDEM can merge your tiles that means you can cover areas with 1/9 arc (if available) and the rest with standard 1/3 arc

[PapaXpress]

I thought that is what I did (though its been over a year now so who knows).

Here is the other other problem I am seeing. The area I selected has 1/9 in the list, but I get this error.

USGSError.jpg

[bnsfsubdivision]

That looks interesting. Try to draw a rectangle from the annotation bar. Then click on the download data button and double click on your poly to download the area. Then you should see a option for the 1/3 arc and 1/9 arc

[Bananarama]

Anyone notice that the new distribution is no longer seamless? I've DEM'd several routes to see if it was something I did, and noted tiles along the borders of the downloaded DEM are missing. Each route had one issue or another. Basically, it looks like an entire tiles row/column is missing (0 elevation). I've been able to repair the missing 1/9 DEM with 1/3 DEM, missing 1/3 DEM with Seamless backups, and SRTM data as a last resort. FWIW, each route area was between 125 and 250 miles in length, and the DEM had been delivered broken into smaller download rectangles (denoted by the red dashed lines displayed from the server and where I believe the problems are found - I haven't confirmed yet, however).

Areas I found issue (so far):

• California (1/9 and 1/3)
• Kentucky (1/3)
• Maryland (1/9 and 1/3)
• Nebraska (1/3)
• Oregon (1/3)
• South Dakota (1/3)
• Virginia (1/3)
• West Virginia (1/9 and 1/3)
• Wyoming (1/3)

I've also noticed that some of the DEM downloaded has a pronounced "step" in places or a raised grid pattern. Easy enough to fix using the smooth tool, but I've never had to do this with the older server. Overall the DEM is OK, and one or two bad sections wouldn't be so bad, but to me the quality of the files has been reduced significantly. I could download smaller areas and allow ReDem to stitch things together, but I'll probably still need to smooth the raised patterns if found.

[hminky]

When I did a preliminary terrain M&Pa route in ReDem I had the border problem with a "canyon" at the border of the DEMs.

I combined the DEM's with MicroDem and it eliminated the "canyon".

Harold

[PapaXpress]

I've had a very similar problem in the past:
http://thegradecrossing.blogspot.com/20 ... r-fix.html

[Bananarama]

Yep - same thing, and a new smaller set solved the missing tile issue (still need to check the raised steps and grid though).

[Bananarama]

A small update.

As mentioned above, I've managed to completely fix my CA test route using smaller DEM areas. Just for laughs, I tried using DEM from my backup, which was several years older than the date of the latest available from USGS. Although both the older and newer DEM are 1/3 arc sec, the older files in comparison to the new look like SRTM 30m crud, and the new has a crispness not found in the older files. If I didn't know better, I would almost believe it was 1/9 data as opposed to 1/3. Right of way and bridge locations are easily discernible, with only a few problematic "step" areas to adjust. Very strange.

[PapaXpress]

You realize by saying that the 1/3 is better than the old 1/3 you just committed me to re-downloading my whole route...

[Bananarama]

You realize by saying that the 1/3 is better than the old 1/3 you just committed me to re-downloading my whole route...

Not necessarily. The backup I had is 5 or 6 years old and released around 2003. The "new" data is 2007 (or there abouts) which may not have been available when I downloaded the first batch. Try a small section and see.

[TDHenderson]

I found you can still do the download by coordinates method, but only for 1 and 1/3rd arc second DEMs. Not available for areas with 1/9th arc second terrain.

http://cumulus.cr.usgs.gov/webappconten ... dTool.html

Trevor

[Bananarama]

Very cool. Thanks for the info, Trevor.

[TDHenderson]

Very cool. Thanks for the info, Trevor.

You are most certainly welcome sir.

Trevor