[FOSS-GPS] Manual tile-scaling control in FoxtrotGPS (and osm-gps-map?) (was: FoxtrotGPS Mapping Library)

[Joshua Judson Rosen]

John Stowers <john.stowers.lists at gmail.com> writes:
>
> > The only issues that I see right now that don't even have work-arounds
> > are that there's no way for to communicate `overzoom bounds' down to
> > osm_gps_map_render_missing_tile() or any of the logic underneath it,
> > and that there actually is no tile-scaling functionality except in the
> > handler for *missing* tiles; if we're to replace FoxtrotGPS' map-drawing
> > code with osm-gps-map, I'd need some sort of `tile zoom' knob to replace
> > the one that we have integrated into our current tile-loader/-renderer.
> 
> Im not sure I understand you here. Could you please explain furthur.
> 
> Are you referring to how osm-gps-map first upscales the low res tile
> while it waits for the high res one to arrive?

Yes--there's no way for me to specify limits on the upscaling.
I'm not sure how much I should be concerned with the upper limit
(tangoGPS used a hard-coded limit of 3; Stefan Fröbe has raised it
to 5 in his geocaching patchset), but there are times when we want
to set a *lower* limit on upscaling--because we don't actually always
want to use higher-res tiles. In particular, the pixel-densities of
some of the phone/tablet screens are so much higher (3x!) than typical
desktop resolutions (which the map-renderers target) that we basically
need to upscale just to make a lot of the details (lines, text, icons)
scrutable by the naked eye at a reasonable distance.

The FreeRunner's screen is ~300 px/inch, so text and icons that are
perfectly legible at 96 px/inch can be extremely difficult to read
from more than about a foot (~30 cm) away, which is absolutely
necessary when driving--as is being to see things at a glance
rather than with intentful scrutiny. :)

Nokia's N-series tablets are somewhat lower-density (~200 px/inch?),
but presumably still high enough to cause issues.

The same issue actually still manifests with lower-density displays
like most laptops (though mine's still ~145 px/inch...), just at
greater distances.

Some other aspects were described on the openmoko community list
<http://article.gmane.org/gmane.comp.handhelds.openmoko.community/55877>:

    So, when you select `fewer, bigger details', the code just decreases
    *pixel-density* and a `zoom-level offset' adjusted accordingly.
    The map remains at the same zoom-level; but the text and icons get
    bigger, the streets and other lines get wider; the amount of
    visual `clutter' decreases, and information-clarity goes up.

    If you select `more, smaller details', the pixel-density is increased
    and the zoom-offset adjusted in the other direction. Again, the map
    remains at the same zoom-level; but the text and icons get smaller,
    the streets and other lines become thinner; the amount of information
    visible at a given zoom-level (the information-density) increases.


If you want to see what I mean, I merged the back-end code into FoxtrotGPS's
trunk at revid rozzin at geekspace.com-20100507055217-p98k7n2pk08fskk7, and the
UI was merged at rozzin at geekspace.com-20100507130010-ykfut9y4nwcw4dn5
(about 2 weeks ago).

-- 
"Don't be afraid to ask (λf.((λx.xx) (λr.f(rr))))."