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USGS GeoPDF
https://forum.transdem.de/viewtopic.php?f=2&t=236
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Author:  geophil [ 04 Jul 2013 09:09 ]
Post subject:  Re: USGS GeoPDF

A few yards have disappeared, of course, but one is still there, according to the aerial image accompanying the topo map, see previes on the USGS historical collection home page. It appears to be Norfolk Southern's DeButts Yard, and certainly bigger than in 1936.

I think the USGS has no longer access to the railroad infrastructure data proper. According to historic sources there was close cooperation between railroads and the USGS in the good old times when the iron horse ruled the country's transportation system. That's apparently over. Even for the road layer, copyright lies with Tom Tom, according to the map legend.

Author:  geophil [ 11 Jul 2013 21:07 ]
Post subject:  Re: USGS GeoPDF

Another example of GeoPDF and DEM, this time for an area, we usually regard as being flat: Chicago. We set our project in the 1940s, in railroad heyday.

One of the misconceptions about DEMs is that they are good for mountainous regions but too much of a hassle for the plains. If we want to see the wider picture, however, we need to understand that DEMs are just one aspect of something we call geospatial data or geo data in short. Geo data is about digital cartography. And taking and processing geo data is a way of transferring the real world to a Trainz route, taking advantage of standardized and automated mapping methods. That's what TransDEM does. This includes DEMs, raster maps and vector maps.

Coming back to Chicago, we should have a look at easily available geo data to assist us. One of the role of the United States Geological Survey is that of a mapping agency, and as such, it has provided excellent topographic maps for more than a century. Recently, many of the historic paper maps have been digitized and are now offered for free download, in a format called GeoPDF.

Brand new TransDEM 2.4 can read these historical maps (with the help of GDAL utilities). GeoPDF files include geo coordinates which make the old paper maps appear as "geo-referenced". This speeds up the process, as each map sheet will be correctly scaled and positioned just by importing it into TransDEM.

I checked the Chicago area for the 1940s and found the 1953 edition which is closest. I downloaded 8 map sheets, each 7.5 min and 1:24,000 scale. One map sheet, Chicago Loop, is a bit wider and extends into Lake Michigan, saving an extra sheet.

Image

The GeoPDF maps come with a so-called neat line which marks the map frame. It is pre-set at 7.5 arc min for this map as well (see semi-transparent pale yellow collar) but can easily be adjusted.

Looking at the legend at the bottom, we find that this is indeed the 1953 edition and that the map projection is polyconic (which is iconic and unique to USGS topo maps). The geodetic datum is North American 1927. TransDEM 2.4 should understand it all.

Image

As each of the 8 map sheets is cut and positioned automatically, they can be combined by simply loading one after the other.

Image

Unfortunately, there is no historical elevation data and we have to get on with present day data. I went for 1/3 arc sec. They say it's flat and you don't need need a DEM. But we'll find it's not completely true. There are hillocks, there are water courses, there's the lake. Why do the terrain shaping ourselves, when the good people at USGS already accomplished this for us?

Image

Now we transfer everything to Trainz and can easily find our way around. The advantage of geo data in Trainz is clearly visible: A mile is a mile. It's all to scale, automatically.

Image

Let's zoom in to the Loop and La Salle St and Dearborn Stations in the early 50s:

Image

Or to the Blue Island area and the Little Calumet River. The DEM has already formed our river bed. One of the many railroad yards seen in the background.

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Need more detail than provided by the topo maps? Add ortho-images. Unfortunately these are present day again. USGS has a historical collection here, too, but very few have been georeferenced so far.

Image

All this was created in less than one hour, and you spend most of the time waiting for the geo data to download or TransDEM to process the data. You can watch and relax and enjoy your coffee or your cold beer.

Author:  WindsorSpring [ 15 Jul 2013 22:02 ]
Post subject:  Re: USGS GeoPDF

Geophil's posting for April 17 shows a box headed "GeoPDF Import..."
Can one access this, and the GDAL functions, within TransDEM?
How? Dropdown menus under "File/DEM" or any of the other tools offer no obvious options.

My version is 2.4.0.0 installed July 7, 2013.
GDAL utilities are installed in my computer in the TransDEM-specified folder.

Thanks,

George

Author:  SharkNose [ 15 Jul 2013 23:22 ]
Post subject:  Re: USGS GeoPDF

George,

Just go to "Raster map", "Open Raster Map...". Or press Shift+O and you should be presented with a similar dialog as this:

Image

It should recognize the .PDF extensions. After you choose your GeoPDF, then you'll see the "GeoPDF Import..." options box.

It sounds like you have the tools installed and ready to go!

Andrew

Author:  WindsorSpring [ 16 Jul 2013 15:57 ]
Post subject:  Re: USGS GeoPDF

Thanks for the help, Sharknose. Unfortunately, when I tried it with one GeoPDF, I got the little rolling, light blue circle telling me the computer was thinking. After about 5 minutes, TransDEM was no longer responding to Windows 7. This was loading a 1964 map for PA_Catasauqua. I did have some success loading PA_Perkiomenville (1953), but none for a 1955 Malvern map. Age clearly is not a factor, though newer ones seem to give more trouble than older ones.

Some of the GeoPDF's might be corrupted or I must be missing something. Zip files still remain in a folder somewhere; I can try this with a freshly-unzipped one. I have used TerraGo on a couple of the files I have tried to open; could this be a factor?


George

Author:  geophil [ 16 Jul 2013 16:13 ]
Post subject:  Re: USGS GeoPDF

Check the TransDEM settings and the path to GDAL. TransDEM tries to find GDAL at the default location but might be mislead. Set it manually. TransDEM will do a cross-check.

The first phase of GeoPDF import, running gdalinfo, should take less than a second and the import dialog should pop up right away.

Author:  WindsorSpring [ 28 Jul 2013 04:14 ]
Post subject:  Re: USGS GeoPDF

Here is a follow-up on my postings on this thread from July 15 and 16.

After a fresh download of the zip file from USGS, I was able to process the same PA_Catasauqua map in TransDEM that had failed earlier.

I suspect my having used TerraGo utilities on the map downloaded earlier may have somehow rendered the GeoPDF unreadable for processing by GDAL utilities and TransDEM. I believe viewing and studying the map in Adobe Reader X causes no later problems for GDAL and TransDEM.

George

Author:  geophil [ 29 Jul 2013 04:57 ]
Post subject:  Re: USGS GeoPDF

Thanks for the update. I am not sure what TransDEM does if gdalinfo hangs or produces unexpected output. Might hang, too.

Author:  ctclark1 [ 03 Jan 2016 00:09 ]
Post subject:  Re: USGS GeoPDF

Super old topic I know, but I thought I'd update that yes, if gdalinfo fails for any reason (in my case it claimed the geopdf's were invalid format) it does not catch in TranzDEM properly. Looks like a catch is needed within the TranzDEM call to gdalinfo to detect exiting without returning the expected data.

Author:  geophil [ 03 Jan 2016 14:38 ]
Post subject:  Re: USGS GeoPDF

There is problem with recent builds on the GDAL Windows site. They do indeed report an error in gdalinfo when opening a geopdf file and TransDEM was not aware of such an outcome. I have done two things. Firstly, the catch you are suggesting has been implemented in TransDEM 2.6. But that wouldn't solve the issue itself. Therefore, secondly, I have uploaded a slightly older GDAL installation package that processes geopdf files without errors. I will send you the address.

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