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Messages - mark03

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16
Hi everyone,

New user here.  Very impressed with Locus!  I hope to use it for hiking in the mountains  near Seattle.  To that end, I've started to research the best way to get US Geological Survey topo maps into Locus (offline).

USGS is transitioning from GeoTIFF to GeoPDF.  A new database of the latest-revised topo maps is now online for free at nationalmap.gov in their "historical topos" collection.  The quality is much better than the "DRG" GeoTIFFs that we have been using for years.  Fortunately, although they are in GeoPDF, the GDAL library (gdal.org) can extract the raster contents and save in a variety of formats.  So GeoPDF is not a problem.

That brings us to the mess that is the mobile map-format space...  Appropriate formats already existed (e.g. tiled geotiff, and a free/open sqlite format---Spatialite and Rasterlite, http://www.gaia-gis.it/gaia-sins/ ---complete with an actual SPECIFICATION  :o).  But, the original players in this space chose poorly (IMO) and so Locus was stuck with a choice:  use a "good" format, that no one else is using, or use formats that actually work with existing software.

Anyway, my goal is to write something in Python to take the GeoPDF rasters and put them in a Locus-compatible format.  I don't want to depend on proprietary solutions like MAPC2MAPC, TTQV4, etc., partly because I am on Linux, and partly because I think it just encourages the proliferation of more useless formats.  GDAL can do most of the hard work here, including the import from GeoPDF, tiling/pyramid creation, and any needed warping / re-projection.  I just need to settle on a target output format, and then I need a spec for that.

Locus sqlite is simple enough, but from what I've been able to understand of some older discussions here, not the fastest?  Then there is RMAP format, and GEMF format, but I can't find documentation or code for either of them.  I guess it is also possible, that by the time I finish a tool, there will be another new format supported!  So I am looking for advice.  What should I target if I want to get this working by summertime?

I was also wondering...
1) Does Locus support multiple image types in its tiled formats?  I exported a simple sqlite and saw that the blobs are PNG.  Can the blobs also be JPEG?  This could save a lot of space, without too much quality loss.
2) USGS topos are [almost] all in NAD27 datum.  Is NAD27 (EPSG:4267) supported in Locus?  Or should I plan on re-projecting into something like WGS84?  I get the idea WGS84 is just "assumed" in some of the simple tile formats... is that right?

Thanks,

Mark

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