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Author Topic: problems at step #2 of Dan's instructions  (Read 5862 times)

dcana

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problems at step #2 of Dan's instructions
« on: July 11, 2013, 04:04:55 PM »
Hello.  Noob here with some stupid questions.  I'm trying to create my first map using Dan's instructions.  First off, what's the advantage of doing this very time-consuming process with all its steps versus just going to various websites and downloading a topo of the area you need?  Is the resultant map somehow better?  Why not just download USGS quads, for example?

I am going to be using the free DEM2TOPO versus the $399 Global Mapper.  The first thing I did wrong is going to the National Map Viewer to download the elevation data.  I downloaded one 24k quad and, 365MB's later discovered that there is no tiff file to use with DEM2TOPO.  BTW, this download, which consisted of elevation data only, actually was more than 700MB of info unzipped.  Why so huge?  So if my state had 100 quads in it, that would take 70GB of information?  Wow.  I've downloaded 24k quads in pdf format and they were only about 30MB in size.  Anyway, if you are using DEM2TOPO how to you obtain the required file in tiff format?  As far as I can tell, you can't get it from TNMV and although the instructions under "Dem2Topo" say, "Make sure you used the USGS DEM LINK (GeoTiff) for Dem2Topo," above it says that "the seamless server is no longer operational."  Wha?

Any help, please?

Boyd

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Re: problems at step #2 of Dan's instructions
« Reply #1 on: July 11, 2013, 04:57:03 PM »
What's the advantage of doing an oil painting when you can just download a copy of a Rembrandt masterpiece? What's the advantage of learning how to play the guitar when you can just download a copy of a Jerry Garcia performance?  ;)

Seriously, you get the idea. The advantage is that you increase your knowledge by learning a new skill, you can express your own creative ideas and you can share them with others.

Are you you asking which is simpler? Download the Rembrandt. Probably, you will never be able to do any better yourself.

To get a little more technical, USGS quads are raster imagery (scans of paper maps). The map in the tutorial is a vector based map. Both formats have advantages and disadvantages. Raster imagery is only viewable within a very limited range of zoom settings - gets all blocky if you zoom in too far, becomes a black blob if you zoom out too far. Vector imagery offers control over what features show at different zoom levels and lineweights remain constant.

But scans of USGS quads have a very different quality since they were hand-drawn. And the often have many little details not found on vector based maps. Each type of map has its uses.

BTW, if you want USGS quads, I think Garmin Birdseye Topo is a no-brainer. Unlimited downloads of USGS quads (plus Canada) for $30. Lots easier than downloading and processing the USGS stuff yourself.

hwstock

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Re: problems at step #2 of Dan's instructions
« Reply #2 on: July 11, 2013, 05:31:15 PM »
Even with the new USGS NED server, you may still have to turn the DEM files from a supplied format (like flt) to tif for DEM2TOPO. I used a batch file I got at the USGS, which in turn requires and installation of the gdal utilities.  Much of the instructions were written when the USGS seamless server supplied tif (Geotiff)-- that server is mainly gone.

I'm using this process for areas outside the USA, where the are no good topo maps, or the available maps are off.  I've even found places in Nevada where the available garmin-compatible maps are off. I'm also interested in some of the newer data, which may resolve some massive errors in the USGS database (e.g.: http://www.summitpost.org/picacho-usgs-map-errors/845687/c-837597).

maps4gps

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Re: problems at step #2 of Dan's instructions
« Reply #3 on: July 11, 2013, 06:34:20 PM »
The 365MB file size is typical of an entire 1x1 degree quad (64 7-1/2 min quads) of 1/3 arc second (10m spacing) NED data.

dcana

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Re: problems at step #2 of Dan's instructions
« Reply #4 on: July 11, 2013, 07:12:51 PM »
What's the advantage of doing an oil painting when you can just download a copy of a Rembrandt masterpiece? What's the advantage of learning how to play the guitar when you can just download a copy of a Jerry Garcia performance?  ;)

Seriously, you get the idea. The advantage is that you increase your knowledge by learning a new skill, you can express your own creative ideas and you can share them with others.

Are you you asking which is simpler? Download the Rembrandt. Probably, you will never be able to do any better yourself.

To get a little more technical, USGS quads are raster imagery (scans of paper maps). The map in the tutorial is a vector based map. Both formats have advantages and disadvantages. Raster imagery is only viewable within a very limited range of zoom settings - gets all blocky if you zoom in too far, becomes a black blob if you zoom out too far. Vector imagery offers control over what features show at different zoom levels and lineweights remain constant.

But scans of USGS quads have a very different quality since they were hand-drawn. And the often have many little details not found on vector based maps. Each type of map has its uses.

BTW, if you want USGS quads, I think Garmin Birdseye Topo is a no-brainer. Unlimited downloads of USGS quads (plus Canada) for $30. Lots easier than downloading and processing the USGS stuff yourself.

I agree.  It's great to be able to create maps to your own specifications and to increase your knowledge, etc., plus it's just very satisfying to do so, but I was just wondering if maps created this way have any real advantage - for example, being routable.  I assume they're not routable as so very few of the maps that people have uploaded are.  Can you see an elevation profile of a proposed route?  I have read some about the advantages/disadvantages of vector maps versus raster maps.  One of the advantages of vector maps is that they take up less space.  This general rule doesn't seem to hold in this case.

Thank you for the help

Seldom

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Re: problems at step #2 of Dan's instructions
« Reply #5 on: July 11, 2013, 07:21:05 PM »
Routable maps are less fault tolerant than non-routable ones, but if you can get Dem2Topo to work out (I use Global Mapper), you can download a copy of GPSmapedit from Geopainting.com and a copy of cgpsmapper personal from cgpsmapper.com.  Those two should cost you a little under $100, and between them you can make routable maps.

You can also get mkgmap for free from the folks at OpenStreetMap.  It will also compile routable maps.

Re. map quality.  I prefer routable maps I've made to those made by others for hiking.  I'd never think of using a routable map I've made to get me out of a bad neighborhood.  But City Navigator has done that for me several times.

dcana

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Re: problems at step #2 of Dan's instructions
« Reply #6 on: July 11, 2013, 07:21:46 PM »
Even with the new USGS NED server, you may still have to turn the DEM files from a supplied format (like flt) to tif for DEM2TOPO. I used a batch file I got at the USGS, which in turn requires and installation of the gdal utilities.  Much of the instructions were written when the USGS seamless server supplied tif (Geotiff)-- that server is mainly gone.

I'm using this process for areas outside the USA, where the are no good topo maps, or the available maps are off.  I've even found places in Nevada where the available garmin-compatible maps are off. I'm also interested in some of the newer data, which may resolve some massive errors in the USGS database.

Where are the flt files?  In the group of files that I downloaded, the one large file (465MB) has an adf extension.

Thanks

hwstock

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Re: problems at step #2 of Dan's instructions
« Reply #7 on: July 12, 2013, 10:07:37 AM »
THIS PROCEDURE might be written up (in a more coherent fashion!) to replace the "cheap" (DEM2TOPO) part of step #2

http://viewer.nationalmap.gov/viewer/

Then at the top of the map on the icon bar, pick the rightmost icon for "eneter coordinates by bounding box" (or whatever it's called) if you want to enter in bounding coordinates by hand, or next to rightmost if you want to use cursor to select on map

Dialog comes up with available data

Check elevation (often near bottom), next

Another box comes up with available data -- arcgrid, grdfloat (flt) or img formats (if available).

So far I've found that (as others suggested) NED actually downloads data in 1 degree by 1 degree chunks.  In US, you can get 1/3 arcsecond in many places; in Mexico, you may be limited to 1 arcsecond. For 1 degree by 1 degree, 1/3 arcsecond data typically downloads as an ~10812x10812 element matrix; with single p floating points, that 4 bytes per element.  That's how you get ~450 MB.

Scripts for converting among file types are at:
http://gisdata.usgs.gov/website/USGS_Raster_Conversion_Scripts.zip

If you look at the scripts, you'll see they just use GDAL_translate.  You can get the GDAL distribution compiled for windows, mac, linux, etc. at various places.  I just use gdal_translate (copying the command line in the script, making obvious substitutions) with
flt (GridFloat) format files.

Typically, DEM2TOPO is limited to rather small files.  I either use a batch file to run gdal_translate to split the flt or tif file into smaller tiles (which are reassembled in GPSMapEdit) or I use gdal_contour to make shp files which I can import into GPSMapEdit.  You'll use either the srcwin or projwin switches with GDAL_translate to extract a portion of the original big tif for processing by DEM2TOPO.  For example, I typically break a 10812x10812 file  into 16 2703x2703 chunks, e.g. with:

(these are the lines in an command-line bat file)
C:\"Program Files"\GDAL\gdal_translate -srcwin    0    0   2703 2703 n33w116.tif n33w116_00.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 2703    0   2703 2703 n33w116.tif n33w116_0a.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 5406    0   2703 2703 n33w116.tif n33w116_0b.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 8109    0   2703 2703 n33w116.tif n33w116_0c.tif

C:\"Program Files"\GDAL\gdal_translate -srcwin    0  2703  2703 2703 n33w116.tif n33w116_a0.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 2703  2703  2703 2703 n33w116.tif n33w116_aa.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 5406  2703  2703 2703 n33w116.tif n33w116_ab.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 8109  2703  2703 2703 n33w116.tif n33w116_ac.tif

C:\"Program Files"\GDAL\gdal_translate -srcwin    0  5406  2703 2703 n33w116.tif n33w116_b0.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 2703  5406  2703 2703 n33w116.tif n33w116_ba.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 5406  5406  2703 2703 n33w116.tif n33w116_bb.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 8109  5406  2703 2703 n33w116.tif n33w116_bc.tif

C:\"Program Files"\GDAL\gdal_translate -srcwin    0  8109  2703 2703 n33w116.tif n33w116_c0.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 2703  8109  2703 2703 n33w116.tif n33w116_ca.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 5406  8109  2703 2703 n33w116.tif n33w116_cb.tif
C:\"Program Files"\GDAL\gdal_translate -srcwin 8109  8109  2703 2703 n33w116.tif n33w116_cc.tif
« Last Edit: July 30, 2013, 03:57:41 PM by hwstock »

 

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