I have had several people send me follow-up emails about converting the USGS eTopos (you can download these from store.usgs.gov), so I thought it might make sense to just post this to the list as a HOW-TO. Apologies for cross-post.
The challenge is to take the GeoPDF that you download from USGS and make it
into a series of TIFFs you can mosaic together. This requires at least GDAL
1.8 and for full functionality you want 1.10.
First, the simplest syntax would be
gdal_translate topo.pdf topo.tif
That would give you a GeoTiff with all the layers turned on, rendered at 150
dpi. Easy enough.
However, depending on what you want, you may want to alter that. For example
the GeoPDF renders differently as you zoom in; it has scale-dependent
rendering. So you may want to change the dpi to a higher number. I did all
mine at 300 dpi which seemed to fit a 24k rendering in ArcMap and looks nice on
the screen.
gdal_translate --config GDAL_PDF_DPI 300 topo.pdf topo.tif
That still has all the layers turned on though. You may want some of them off.
For example, you may want to turn off the NAIP data and the UTM grid (like I
did). If so you can specify certain LAYERS to turn off, first you have to
figure out what they are with this (this requires GDAL 1.10):
gdal_info -mdd LAYERS topo.pdf
will return the metadata and a list of layers something like this:
<snip>
Metadata (LAYERS):
LAYER_00_NAME=Map_Collar
LAYER_01_NAME=Map_Collar.Map_Elements
LAYER_02_NAME=Map_Frame
LAYER_03_NAME=Map_Frame.Projection_and_Grids
LAYER_04_NAME=Map_Frame.Projection_and_Grids.Projection_Coordinate_Values
LAYER_05_NAME=Map_Frame.Projection_and_Grids.Geographic_and_Grid_Ticks
LAYER_06_NAME=Map_Frame.Projection_and_Grids.Projection_Line_Mask
LAYER_07_NAME=Map_Frame.Projection_and_Grids.Grid_Lines
<snip>
LAYER_28_NAME=Map_Frame.Land_Cover.Woodland
LAYER_29_NAME=Images
LAYER_30_NAME=Images.Orthoimage
<snip>
So I'm looking to get rid of layer 7 and layer 30. The syntax for that uses
the layer name like this:
gdal_translate --config GDAL_PDF_DPI 300 --config GDAL_PDF_LAYERS_OFF
Map_Frame.Projection_and_Grids.Grid_Lines,Images.Orthoimage topo.pdf topo.tif
This only works for the new 2011/12/13 maps. The historic maps are scanned
images, so they don't have any real layers. They are just one raster image in
a PDF. So you would just do
gdal_translate --config GDAL_PDF_DPI 300 topo.pdf topo.tif.
What you get in both cases is an output GeoTIFF of the topo map. The map will
have all the collar info, so you will then have to crop the images, remove the
collars, and mosaic the slivers to get a seamless mosaic, but that is just done
the same way as any other imagery collection. That process is to simply:
Crop the image to its minimum size with gdalwarp
Burn some null value to the remaining collar slivers with
gdal_rasterize -i -burn <etc.>
Mosaic the neighboring tile data into the sliver with gdalwarp
One other cool thing about the GeoPDF with its scale-dependent rendering is
that you could create topos at different dpis (scales) and thus make your
overviews look like what a 100K or 250K topo would look like (well with the new
ones anyway, not the historic ones).
Don't forget to RTF(riendly!)M http://www.gdal.org/frmt_pdf.html
===============================
Michael Smith MS GISP
State GIS Manager, Maine Office of GIS
State of Maine, Office of Information Technology
michael.smith _at_ maine.gov 207-215-5530
Board Member, Maine GeoLibrary
Education Chair, Maine GIS Users Group
State Rep, National States Geographic Information Council
[cid:image001.jpg@01CF49A3.32BF2BC0]
State House Station 145
51 Commerce Drive
Augusta, ME 04333-0145
69o 47' 58.9"W 44o 21' 54.8"N
<<inline: image001.jpg>>
_______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
