[Xastir] [tiling] reading tiles slow

[Jerry Dunmire]

Hi Piotr,
Yes, it is slow. As I noted in the README file, performance will not
approach that of tangoGPS, or any other native OSM system. The root of
the problem is that projection mapping that must occur between the
Mercator projection of OSM tiles and the 'un-projected' Xastir view.
Each pixel requires a multiple trig operations. Another factor, though
far less, is scaling between the 18 zoom layers of the OSM tiles and
the 32-bit zoom of Xastir. That zoom transformation also requires a
pixel-by-pixel transformation, but the math is linear and therefore
far faster than the projection mapping. Of course it is likely that
someone can improve on my code, but I can't imagine that it will ever
approach the speed of programs that do not have to do projection
mapping.

73,
...jerry
KA6HLD


On Fri, Aug 13, 2010 at 11:53 AM, Piotr Gluszenia Slawinski
<curious at bwv190.internetdsl.tpnet.pl> wrote:
> i've installed new xastir with tiling support on several machines,
> and on all of them 'reading tiles' takes lot of time...
> compared to how quickly tangogps can render tiles, it's like
> (on p233 tablet with 64M ram) : ~2s (tango) vs. ~20s (xastir)
>
> what takes so much time? is it possible to fix it somehow?
>
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