[Kstars-devel] Interesting HTM timing results

[Jason Harris]

Hi James,

On Sunday 28 May 2006 18:39, James Bowlin wrote:
> I find this result very interesting.  Don't bet the ranch on it because
> I could well have made a terrible mistake somewhere, but if it holds up
> it implies that even though intersections on the finer meshes are more
> expensive, it turns out to be time well spent since it is saving us time
> in the long run by doing a better job of reducing the number of stars
> that need to be clipped manually.   It would also mean that my idea of
> saving time by using a courser mesh for the wider views would have
> actually slowed things down!  Of course in the wider views, people
> generally clip the dimmer stars in which case the benefit of the finer
> mesh would be greatly reduced.  AFAIK, the HTM's will at best give us
> a factor of 2 speed improvement when it comes to drawing the entire sky
> (I think we only draw 1/2 of the sky at a time).  This makes me think
> that we also might be able to use the HTM to clip stars that are under
> the horizon when we are in the mode of just drawing that area as green.
>
Yes, very interesting tests.  The final answer to all of this will come when 
we actually implement it, of course...

I think below-horizon stars will be more quickly clipped on the basis of their 
(already known) Altitude coordinate than with a half-sky HTM slice.

> The chart above was produced by 21 lines of Perl code.  I'd be glad to
> post it if anyone wants to check my work.  Please consider these results
> to be an alpha release.
>
> For debugging purposes, I'd really like to try to implement the dcop
> drawLine() feature.  Actually, I'd like to implement drawLineRaDec()
> so the lines would be somewhat fixed to the sky.  Then we would
> just need an eraseLines() for starting over.  The lines could all
> be stored on a stack somewhere.   I would draw the triangles
> so we can get an image of what is going on with these meshes and
> intersections.

We should have this function, but for your purposes, it might be better to 
just add a "HTMComponent" to the skycomponents directory.  We could add a 
hotkey that toggles the HTM lines on/off.  I could pretty quickly add this 
component when the time comes.

Jason

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