[Kstars-devel] Clipping Miky Way polygons

[James Bowlin]

On Saturday 10 June 2006 13:25, James Bowlin wrote:
> I'm not certain that shrinking down the size of the polygons is going to
> totally solve the two artifact problems but it will certainly reduce
> them perhaps to a level where they become acceptable.  Reducing the size
> of the polygons will also make a spatial index more effective if we want
> to use it for doing course clipping of the Milky Way.

The smaller polygons work great!  I converted 2 out of the 11 current regions
to smaller polygons and both artifacts are almost gone.  The "inside-out"
artifact is totally gone and the clipping lines are just barely noticeable. 

I'm putting all of the Milky Way data into a single file called milkyway.dat.

I am going to convert the other 9 regions to smaller polygons.  I took a
snapshot of the outlines of the polygons in the first two regions so you
can see what they look like.

I'd bet that with the polygon and line clipping we could cull out more
than half the points of Milky Way data and not lose any resolution on
the skymap.  I just verified this.  It looks like we can reduce the number
of points by at least a factor of two with virtually no degradation.  We
can reduce the point density by a factor of three with limited degradation.
I am able to verify this by using both the old and the new data in KStars
and plotting the new data directly on top of the old.

There was no need for using a different data structure for the lines (as
opposed to the filled polygons).  I didn't even need to eliminate the
first or last point from each polygon since the existing algorithm to not
draw lines between two points that are "far away" still works like a champ.


-- 
Peace, James