Using DEM data

[StorkNest]

Thanks that worked perfectly.

Now I'm looking for the following information, been searching through other topics but some information appears sketchy.
1 - How to merge the USGS quads available from either http://data.geocomm.com/ or http://www.mapmart.com/ together. I have a few I believe 30M quads from the first and 10M from the second. Tried looking through the MicroDEM help file but the methods listed show using features either grayed out or not available, one method went from step 5 straight to step 8! Areas I'm looking to merge are not huge.
Areas A and B contains 3 quads each.
Area C has 4.
Area D has 6, maybe 7.
2 - What format to download seamless data in from http://seamless.usgs.gov/ and what folder to put it in. Latest MicroDEM has in the \mapdata folder a \DEMs folder (seperate from \usgsdata) and under \mapdata\usgsdata there are folders for \DEM-NED, \NED-NINTH, \NED-THIRD, \SRTM-1 and \SRTM-3. I want to try this mthod to see any differences in results.

 

[StorkNest]

After more fiddling, it appears I have to do any merges when I first open MicroDEM before opening anything in it. The IN <-> OUT button only works then, once I open something, it grays out and is unusable until next time I start the program.
Managed to merge Areas A and B fine. Area C merged but it looks like there are rectangular gaps between two of the quads I'll have to figure how to fill that.
Area D with 6 quads isn't merging well, 2 quads are giving trouble and will not add on to the merge. I tried redownloading them from MapMart instead of Geocomm, same thing. The finished merge with quads lettered is supposed to be a sideways P like this:
ABCD
__EF
B and C are the problems, when I run the merge either selecting multiple DEMs at once or singly, I get this message.

1660289.DEM.SDTS.TAR.gz   meters z range: -1.1 to 97.8 m UTM zone=18  NAS-C  Level 2  Horizontal spacing: 10
[COLOR=red]1705847.DEM.SDTS.TAR.gz   meters z range: 0 to 80.1 m UTM zone=18  NAR-C  Level 2  Horizontal spacing: 10[/COLOR]
[COLOR=red] Incorrect datum; not included in merge[/COLOR]
1705869.DEM.SDTS.TAR.gz   meters z range: 0 to 106.4 m UTM zone=18  NAS-C  Level 2  Horizontal spacing: 10
1706056.DEM.SDTS.TAR.gz   meters z range: 23.6 to 174.8 m UTM zone=18  NAS-C  Level 2  Horizontal spacing: 10
[COLOR=red]1706105.DEM.SDTS.TAR.gz   meters z range: 5.8 to 169.6 m UTM zone=18  NAR-C  Level 2  Horizontal spacing: 10[/COLOR]
[COLOR=red] Incorrect datum; not included in merge[/COLOR]
3683230.DEM.SDTS.TAR.gz   meters z range: 0 to 384 m UTM zone=18  NAS-C  Level 2  Horizontal spacing: 10
Merge: 4  with: 4252 cols, 2796 rows

Ones in red are the problems. How do I fix Incorrect Datum?
Thanks in advance.

 

[geophil]

You will probably have to convert those DEM files with the wrong datum first. NAD27 instead of NAD83 I would suspect. MicroDEM should have a function to accomplish this.

But - why don't you simply define your individual DEM in Seamless Server and download it in one rush?

 

[StorkNest]

Seamless I'm still trying to understand:
1 - Whether I should get SRTM or NED or something else.
2 - What folder it goes into.
See my item 2 three posts above this one.
Thanks for the info, those two are NAD83 while the others are NAD27.

ADDITION: Seems I figured out the seamless data, got downloads to work (I think).
Now I cannot get the TIGER lines to show in MicroDEM. I am having the same problem as the poster of this topic:
http://forums.auran.com/trainz/showthread.php?t=24142&highlight=TIGER
I did the correct method that Balkoth listed in the fourth post but after it looks like it processed the TIGER data, nothing shows on the image. I have the correct county data from Geocomm, I downloaded the zip file and saved it to C:\mapdata\tiger without changing the name. Did I miss some step such as renaming the folder or placing it in the C:\mapdata\tiger a certain way?

FURTHER ADDITION: Nevermind, I didn't have the right sub-folder setup in C:\mapdata\tiger, I just used the main TIGER folder. Fixed.

 

[StorkNest]

I think I have this figured out. Got the 4 DEMs done and they show in TRS2004.

My only issue is 2 have more boards than I want due to how they were made (no way around having those extra boards). Is it normal to find yourself deleting baseboards from finished DEMs before releasing them? The GND files are pretty big as is.

 

[JCitron]

Dermmy--

Thanks for the guidance. Seems to be working although in some maps the textures don't show up in the minimap. Also, is there a color convention for the features? It seems the shorelines are blue, surface streets are red, highways are orange, tracks are blue-gray (I'm a little colorblind). Is that about right?

Thanks again. -Walt

That's about right. Power lines are really dark red just to let you know. One of the things that I find helpful is to view the area if you can, from an aerial photo to get an idea what else goes in the area besides the tracks, roads, and water.

John

 

[StorkNest]

I have successfully made some DEMs, still have a couple of questions.

1 - Has anyone ever modified the Tiger file data image when changing it from BMP to TGA? Sometimes I get things like rail lines showing as black, red or a darker shade of teal. So I was wondering if it is fine for HOG if you modify the Tiger image.

2 - Have you ever cut an image into seperate parts? Say you have a large area and you want to split it into 2 or more so HOG will make more than one GND file, then you save them as seperate DEMs to be merged. Or you get a section of seamless data with rail lines you don't want so you modify the image by cutting them out. Is that fine?

Thanks.

 

[geophil]

1 - Has anyone ever modified the Tiger file data image when changing it from BMP to TGA? Sometimes I get things like rail lines showing as black, red or a darker shade of teal. So I was wondering if it is fine for HOG if you modify the Tiger image.

The way HOG works, it maps an input colour value to a ground texture. One of the files delivered in the HOG package defines the colour-to-texture mapping. This mapping will only succeed if your TGA image contains the colour values HOG expects - to the very last bit.

2 - Have you ever cut an image into seperate parts? Say you have a large area and you want to split it into 2 or more so HOG will make more than one GND file, then you save them as seperate DEMs to be merged. Or you get a section of seamless data with rail lines you don't want so you modify the image by cutting them out. Is that fine?

HOG does not know anything about geographic coordinates, it simply relies on images, one for the DEM, one for the map. These two images must exactly match each other for each module to be built.

You can create multiple modules but you are completely in charge of providing the proper grid. You have to cut your DEM and your map image files at the correct positions, multiples of 72 pixels (one baseboard), plus margin overlap.

I have never tried this myself, preferring the automatic way, but I can't see any reason why you should not be able to create modules for seamless merge by hand.

 

[Vern]

I did try in the early days using HOG to create a succession of sub-sections which were joined into the whole. However despite careful contour tracing and shading, they never did quite match at the join, requiring considerable work on the edges to match up the heights.

Transdem on the other hand (shameless plug for you, Roland) avoids that and does so much more into the bargain. I can thoroughly recommend the slight financial outlay as a very sound investment if you are interested in geographically accurate routes.

 

[Tokkyu40]

If you follow the color code exactly you can add or remove rail lines on the Tiger image. I use 2 pixel lines to match the original and draw the new track wherever I need it.
I've used that to recreate tracks that have been gone long before the USGS started collecting Tiger data.

Claude

 

[cgwright]

Might I join Probe and Vern in recommending TransDEM? It will do everything you want, at a very reasonable price.

I followed the tutorial blindly, with no previous knowledge, and had everything done in half an hour.

Regards
Chris