[Xastir] Transmit Shapefile ?

[Tom Russo]

On Fri, May 16, 2008 at 02:10:19PM -0400, we recorded a bogon-computron collision of the <mckeehan at mckeehan.homeip.net> flavor, containing:
> If my memory is correct, there is some method to send area "shapes" with APRS.
> I've got it in my mind that firenet sends something like this for weather
> data.
> 
> I was wondering, is it possible to use similar techniques to transmit a
> shapefile? Specifically, I have a bicycle route for an upcoming event that I
> would like to share with others via APRS. Is this possible?

The wxsvr "shape" information only supports a limited number of points, so
it would not be straightfoward to send a whole shapefile over APRS.

That information is passed in an object's comment field using a string
of characters to represent each vertex.  As such, it is limited to the 
length of the comment field, which works out to a maximum of 16 points if
you put nothing else in the comment.  Since wxsvr puts information about
the area into the comment as well, their objects tend to be less than 16 
points.

If you care to chop your route up into segments of 16 points or fewer, 
you could transmit your route as a collection of objects.

There is a routine I wrote in util.c called "makeMultiline" that is currently
unused in xastir.  It takes an array of lat/lon points and constructs the
string needed to transmit that as a multiline object.  It also computes
the center of the bounding box of the points, and this is meant to be used
as the coordinates of the object point (from which the other points are 
represented as offsets).

I have occasionally used that routine in a standalone code to generate
the text for a multiline object, then cut and pasted it into the object
creation dialog box in xastir.  I put it in xastir's source code because it
seemed someone might want to do something with it someday, but so far it 
hasn't been used.  Maybe you'd like to try.

-- 
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
 "It's so simple to be wise: just think of something stupid to say and
  then don't say it."  --- Sam Levinson