[Xastir] Re: Interesting APRSdos map!

[Curt, WE7U]

On Sun, 7 Mar 2004, Curt Mills wrote:

> On Sat, 6 Mar 2004, Henk de Groot wrote:
>
> > Yes, I guess it could be done in two steps, first draw in memory on an
> > extended -360/+360 +90/-90 grid and then display the final bitmap centered
> > as the user would like it. The -180 to -360 area should then be
> > superimposed on the 180 to 0 memory area (bitwise OR) and +180 to + 360 on
> > the -180 to 0 memory area; that's easy enough with a bitmap.

Thought about this a bit more during my long commute this morning.
If we extended the area as you suggest, we could just draw the darn
thing and then translate the points.

If we did it the way I was suggesting (algorithmically), we'd need
to check each polygon and vector to see if it was going across a
boundary.  If so, we'd have to find the intersection points with the
boundary and split the object into two (or more) pieces, drawing
each separately.

With your method, we take a small performance hit for the copy-OR
operation and a larger memory hit.

With my method we'd take no memory hit, but might take a big
performance hit for the computations.  We'd be adding more checks
for EVERY vector/polygon object, plus more computations for the few
objects that went across a border.

--
Curt, WE7U			    archer at eskimo dot com
Arlington, WA, USA		http://www.eskimo.com/~archer
"Lotto:    A tax on people who are bad at math." -- unknown
"Windows:  Microsoft's tax on computer illiterates." -- WE7U
"The world DOES revolve around me:  I picked the coordinate system!"