[Xastir] County borders

[Curt, WE7U]

On Mon, 15 Feb 2010, Craig Anderson wrote:

> When Xastir starts up it will "index" the maps it has.  This is a
> process where Xastir looks at all the map data files it has (the
> "edges folder" you have) and matches the data format of each map
> file with a dbfawk file (usually in /usr/share/xastir/config).

Close.  Indexing involves figuring out the extents of each map and
writing them to an index file.  Xastir then uses that index file to
decide which maps may have some ingress into your current display,
and which ones are totally outside the display.  It's a faster way
of choosing maps when you have a lot of maps selected or Auto Maps
turned on.

Matching up to the dbfawk file occurs at the point of map
loading/display as I recall.

Indexing on startup only occurs if you have that option turned on.
I turned mine off because I don't change maps often anymore.  I
manually force a reindex when I do add/change maps.  Faster startup.


> The
> dbfawk file will determine how that map data is displayed; i.e.
> the process of changing colors, sizes, zoom levels, or other
> display attributes is controlled by the control statements listed
> in the dbfawk files.
>
> Xastir also determines the coverage area of every map file to
> determine when it needs to dig through that file based on the area
> it is trying to display on screen.  Every time Xastir displays a
> screen it determines all the map files that are touched by that
> view and uses the matching dbfawk file to search through that map
> file and pull out only the objects that fit in that screen view.

Yes, except it only looks through the map choices you have selected,
unless you use Auto Maps.  Most people don't use Auto Maps anymore.


> Unfortunately, changing how an object is displayed is not a very
> easy process.  And it is not very fine-grained.  if you change a
> dbfawk file you will change the display attribute of that style of
> object in *every* map Xastir displays, not just the 3 or 4
> counties you want.

There is a way, but it involves dropping a dbfawk file (with
matching name to the map file of interest) right into the directory
with the map file.  I _think_ that overrides the global dbfawk
files, but Tom or others could probably answer this better than I.


> To do this correctly you need to know the
> contents of the map files and the dbfawk files.  Use the "dbfinfo"
> program to show you the format of the map data file so you can
> know which dbfawk file is digging through that map file (because
> the schema in the map file matches the schema listed in the dbfawk
> file).  Then you can figure out which map feature you want to
> display and how to set it's color, size, zoom level, etc.
>
> Then comes the issue of layering your map objects so that roads
> and streams get displayed on top of color fills and not covered by
> them.  This happens in the Map->Map Chooser->Properties dialog
> box.

Lots of good info above.  Thanks for writing it!

-- 
Curt, WE7U.                         <http://www.eskimo.com/~archer>
    APRS:  Where it's at!                    <http://www.xastir.org>
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