[Xastir] help with topo lines overlayed

[Tom Russo]

On Tue, Dec 14, 2004 at 10:58:14PM -0700, we recorded a bogon-computron collision of the <jradio at hitesman.com> flavor, containing:
>  Ok, I've seen the sample shots of topo lines overlaied on Terraserver 
> imagry and other maps.  And I've read in the README.MAPS that this is 
> done with SDTS data.  There's also a link that suggests getting the 
> "hypsography" but I can't find any such beast at the link provided.  I 
> do find the National "Hydrography" Dataset.
> 
> I have support for everything compiled into Xastir including GDAL/OGR 
> but even after reading all the docs and some pages google found I can't 
> figure out where to get the data files to do topo lines for my area.

README.MAPS points to
http://edc.usgs.gov/geodata/
and that is indeed where you'd find them, though it takes a little digging.  
Click on the tab that says "1:24k DLG" then use "FTP by State", and dig down 
to find the data you want.  The 1:24k data is organized under the states by 
the USGS 7.5 minute quadrangle names, and under each quad's directory are 
subdirectories with the different layers that were used to create the 7.5 
minute topo maps.

[having the "24kgrid.shp" file and the dbfawk I made for it on 
http://www.swcp.com/~russo/shape_web/ helps here, as you can use it to see 
what quad names are in the area of interest to you if you aren't already
sure which ones you need]

In those subdirectories are usually the most recent tarball of that type
of data.  Sometimes there are further subdirectories with older data.  
Sometimes it's hard to tell which is more recent than which without digging 
into the files themselves.

Each tarball contains a whole slew of data files, which together make up
the SDTS transfer for that data layer --- you need to untar each tarball into
a separate subdirectory, because each tarballs will have files with the
same names as other tarballs even though they're of different areas, and 
everything gets ugly if you try to dump them into one directory.  For example, 
each hypsography tarball will have files like HP01IDEN.DDF, HP01IREF.DDF, 
HP01CATD.DDF, etc., 

A word of caution:
Some of this data is very, very old --- you might find that the layers
are from a 1960 version of the topo map --- but hypsography probably didn't
change so much as to make it useless.  Not so of roads.  The freely 
downloadable road layer for one of the quads I drive through every day still 
shows US Route 66, and has no sign of Interstate 40.

There are some tools you can use to explore the SDTS data, but they're hard
to find source code for.  Last time I looked it took a lot of googling
and I only found one place:
ftp://ftp.blm.gov/pub/gis/sdts/dlg/c_code.zip
I highly recommend having these tools if you're gonna monkey with SDTS files
in any depth other than displaying them in xastir.  

HTH,
T.

-- 
Tom Russo    KM5VY     SAR502  DM64ux         http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 http://www.qsl.net/~km5vy/
 "That which does not kill me is better than that which does."
    --Irving Nietzche, lesser known of the famous Nietzche twins