[Xastir] Weather map question

[Tom Russo]

On Mon, Jun 18, 2007 at 02:07:07PM -0500, we recorded a bogon-computron collision of the <lee.bengston at gmail.com> flavor, containing:
>  I got the WMSradar to overlay the Tigermaps by setting the radar map to a
>  higher layer - worked great.  Besides the layer settings, what do the other
>  settings in the map chooser properties mean?  

> [Filled (yes/no/auto),

This is for vector layers, especially shapefiles.  Yes means that polygons
present in the vector layer are always filled, no means they're never filled,
and auto means that some method of choosing automatically is used.  For 
shapefiles that method is either the hard-coded method if you don't have
PCRE installed or compiled with "--without-dbfawk" and dbfawk otherwise.

Leaving this at "auto" is reasonable unless you find you have a filled-polygon
layer that you would rather have unfilled, or a polygon layer that's not
being filled when you want it to be.

>  automaps (yes/no)

Automaps is an old way of choosing which maps to display.  It's somewhat
unnecessary now (although many people continue to find it useful) since
we have much finer-grained control by using the min/max zoom level settings.

If you turn on automaps in the Map menu, the automap algorithm is used.  
The automap yes/no setting lets you exclude some maps from that algorithm.

Unless you use Automaps, just ignore that setting.  And I recommend that you
not use automaps unless you have a very specific use for it.  I advocate
removing automaps from the code, but there are still enough people who find
it useful that we won't be doing that anytime soon.

>  and USGS DRG (yes/no/auto)]

USGS DRG maps are digitized topo quadrangless from the United States Geological 
Survey (DRG stands for "Digital Raster Graphics").  The USGS uses a standard
color palette of only 12 unique colors for all of their topographic maps, 
which makes it pretty easy to do a cool thing:

There is a setting in the Map->Configure menu that allows you to pick a subset
of the twelve colors to display --- any pixel in a USGS DRG map of one of the 
deselected colors is simply not drawn.  The cool thing is that if you
select, say, only the color brown, then only the pixels that contain contour
lines will be drawn, and anything you have in a lower map level will show
through.  This allows you to overlay the USGS's contour lines on top of any
other map data (such as aerial photos).

This was originally implemented in such a way that the color selections
were applied to all GeoTIFF files, which was a problem if you had a mixture
of USGS topo maps and other types.   The setting in the map choose was
added to fix that implementation problem.

USGS DRG files obtained directly from the USGS contain a nifty piece of 
metadata that allows you to recognize them.  However some GIS departments
tweak USGS topos (either to strip out the map color, or to compress them,
or to otherwise monkey with them) and sometimes this process removes
that bit of metadata.  So "Auto" means 'look in the file for that bit of 
metadata, and if you find it, apply the settings in the 
"Map->Configure->Configure USGS DRG" dialog, otherwise do not use
those settings'.  "No" means "This file is not a USGS DRG topo so do NOT 
apply those settings" and "Yes" means "This really is a USGS topo, even if it 
lacks the metadata that would normally identify it as such"

You can pretty much always have this at "Auto" unless you've got a bunch of
USGS-derived, but defective, topo maps in GeoTIFF format.
-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 http://kevan.org/brain.cgi?DDTNM
"And, isn't sanity really just a one-trick pony anyway? I mean all you get is
 one trick, rational thinking, but when you're good and crazy, oooh, oooh,
 oooh, the sky is the limit!"  --- The Tick