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PostPosted: 13 Nov 2018 19:19 
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Joined: 19 Feb 2011 00:32
Posts: 35
Normally, the process I follow to utilize a topo map in Trainz starts out like this:

1. Download a GEOPDF from the USGS National Map Download page
2. Open it in Transdem (Open Raster Map)
3. Mask the margins (click "Define Transparent Margins with Polygon Mask" twice)
4. Convert to UTM
5. Save the Georeferenced Raster Map

Works great with topo maps published before 2018. However, when I attempt to open new USGS topo maps (published in 2018), I get unexpected results. In Step 2, Transdem takes a very long time, then asks for information (coordinate system, zone, hemisphere), and in Step 3 it doesn't properly find the margins. Apparently the format of the latest USGS GEOPDFs has changed (they refer to them as GEOSPATIAL PDFs instead of GEOPDFs). Would a newer GDAL package help? I'm still using the GISInternals package I downloaded from the Transdem site.


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PostPosted: 14 Nov 2018 19:02 
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Joined: 05 Jan 2011 16:45
Posts: 1463
Kookaburra wrote:
Apparently the format of the latest USGS GEOPDFs has changed (they refer to them as GEOSPATIAL PDFs instead of GEOPDFs). Would a newer GDAL package help? I'm still using the GISInternals package I downloaded from the Transdem site.
Can you point me to a map sheet that has these issues? I will probably have to analyse this in debug mode. It's possible that they switched to a different coordinate system, one that TransDEM does not recognize. For the margins, or neat-line as they call it, that took me completely by surprise when I discovered this feature in USGS maps. I didn't even know it existed. But it's optional. And I haven't seen it in any GeoPDF map published by other agencies.

In the meantime you can try a newer GDAL build, but I have my doubts. Anyway, that build must include the GeoPDF library.


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PostPosted: 14 Nov 2018 19:41 
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Joined: 19 Feb 2011 00:32
Posts: 35
Thanks. Here's an example, a USGS 7.5 minute map for Felton, CA published in 2018...

https://prd-tnm.s3.amazonaws.com/Staged ... TM_geo.pdf


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PostPosted: 15 Nov 2018 18:55 
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Joined: 19 Feb 2011 00:32
Posts: 35
Just a small update. I've noticed that USGS 2018 "Geospatial PDFs" are perfectly usable in Transdem (and, ultimately, in Trainz) provided that I manually enter the correct coordinate system, zone, and hemisphere, and manually crop the margins. In other words, I can use the new maps. The process just isn't as automated as with older USGS Topo maps.


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PostPosted: 17 Nov 2018 18:23 
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Joined: 05 Jan 2011 16:45
Posts: 1463
After the analysis of two of the 2018 edition topo maps I think we are facing three issues with these latest USGS GeoPDFs. Unfortunately, from the TransDEM side we can only handle one.

  1. Long processing time: This may have to do with the larger file size but I don't know where that is coming from. Lower compression for the embedded ortho-image? It appears to have the same resolution as older editions (it's still a 1:24k map). The waiting time is caused by gdal_translate. When monitoring its output, we see a lot of error messages
    Code:
    ERROR 1: Pos = 54602588, insufficient arguments for Marked Content
    ERROR 1: Pos = 54602596, insufficient arguments for Marked Content
    ERROR 1: Pos = 54602599, insufficient arguments for Marked Content
    ...
    before it is actually starting the output conversion which then takes as long as it did before. I couldn't find any meaningful explanation for this error messages and I don't know whether those errors are relevant in any sense. I have also run the latest GDAL build from the GISInternals site but get the very same results.
  2. Geo coordinate system: Here I found a few subtle changes in the meta data description. It's all text and that makes it always difficult to parse. NAD83 has become GCS_North_American_1983, and parameter names which used to be all lower case are now starting with uppercase letters.
  3. The neatline (margins):This doesn't make any sense at all now. Some corner points even exceed the overall image dimensions. I cannot imagine that this is by intention. Perhaps we should send a bug report.

One gets the impression that a new software has been employed to produce the 2018 GeoPDFs.

I will prepare a TransDEM update that takes care of the new keywords and spelling in the geo coordinate system encoding. I will also add constraints to the neatline processing so that all given points will lie within the limits of the image. At least you will then be able to manually drag the corner points to the right position.


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