Date: Mon, 17 Apr 2000 18:15:30 -0400 (EDT)
From: Bob Bruninga
Subject: [aprsspec] Re: Query Lines Boxes and Etc


On Mon, 17 Apr 2000, Sadowski, Allan wrote:

> An interesting thought...   If you could have a LAT/LON and a sequence of
> vectors (length and direction) then it'd be a short notation for an object
> path... so tornado - hurricane paths could be displayed... hmmm interesting
> in the case of a hurricane if each segment equated to an hour in time... 

What I had originally proposed was before we began using BASe-91
characters and compressed format, so here is what I would propose today
using the existing ITEM format (compressed).

  )NAME!\yyyyxxxx)SSSxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyx
  ^^^^^^^^^^^^^^^^

  WHERE this is just an ITEM named "NAME" in compressed format using
        the symbol characters of "\)" (This is a currently undefined
        SYMBOL).  The YYYYXXXX is the starting point anywhere on the
        planet to the nearest foot.

        The first 3 bytes in the COMMENT field for this ITEM is the
        SCALE in base 91, giving a scale anywhere from 1 foot to
        142 miles (per line segment)

        The remainder of the line are any number of pairs of X/Y offsets
        from each previous point.  Each offset is a single
        base 91 number with anything above 45 being positive and below
        45 being negative.

The result then can be any multifaceted shape from a small scale of 
about 1 foot per line segment up to an object 142 miles on a side.

NOtice that this is a completely legal ITEM.  Its just that the SYMBOL
(ICON) has this unique set of display rules...

de WB4APR.

Thus, I can transmit to you in ONE PACKET a complete MAP of the route from
the nearest INTERSTATE to my front door in a single packet...




Date: Tue, 18 Apr 2000 15:10:17 -0400 (EDT)
From: Bob Bruninga
Subject: [aprsspec] Re: Query Lines Boxes and Etc


On Tue, 18 Apr 2000, Bob Bruninga wrote:

> > >By using an origin and base91 offsets, then we could send polygons(or
> > >contiguous line segments with as many as 40 points in a single packet.

> How about if we defined the SSS scale factor to be in Meters.  Then
> the range of scale would be from 3 feet to 420 miles before you would have
> to go to multiple segments.

BETTER IDEA:  The offsets and scale should  all be done in terms of
LAT/LONG (not meters) to avoid any complex spherical trig functions.  If
we let the units be in terms of .000001 degree of LAT/LONG, then we get
approximately 1 meter precision.  AND since this is just a "shape" then if
we define the symbol character of ")" to be a polygon then it can be
transmitted in ANY existing APRS POSIT, OBJECT or ITEM report.

So the format wouild be:
*  ANY POSIT, OBJECT or ITEM defines the origin of the polygon
*  SYMBOL of "\)" indicates it will be a polygon
*  Comment field format is then:

   CSSSxyxyxyxyxyxyxy...

   Where C is the color 0-15 (or 16-32 means FILL the polygon)
   SSS is the scale factor in units of .00001 degree of lat/long
   xy are offset pairs between each subsequent point

Thus the following comment field on an OBJECT located at 3847.04N
07710.53W could completely define the Washington DC BELTWAY:

   +!$