[OSM-dev] "Retina" tiles - best way to support them?

[Robert Joop]

[Since I kicked off this branch of the thread, I take the liberty of
following up even though two weeks have passed, due to vacation.]

On 12-07-05 09:44:25 CEST, Frederik Ramm wrote:
> On 06/27/2012 01:10 AM, Robert Joop wrote:
> >>3. Modify style as per 1., double size of meta tiles to 4096x4096, and
> >>double size of tiles to 512x512. This avoids the increase in font
> >>nastiness *and* it has the nice effect that one "Retina" tile at a
> >>certain zoom level shows exactly the same content as a normal tile, just
> >>on 512x512 instead of 256x256 and therefore at twice the resolution. It
> >>would, however, require clients (OpenLayers et al.) to work with the
> >>larger tile size.
> 
> >This option sounded best to me as well.
> 
> >>I just tried this out and found that, on a standard non-mobile
> >>Firefox browser, OpenLayers displays the new 512x512 tile just fine,
> >>it scales it to 256x256 in the browser. I can then use the browser's
> >>"zoom" function to blow up the OpenLayers display and while
> >>everything becomes jaggy when I do this with normal tiles, the map
> >>still looks nice when using the double resolution tiles. Does this
> >>mean that it would be an acceptable viewing experience for mobile
> >>users as well?
> >
> >Most likely, I’d guess.
> >I’d like to try it on some devices with pixel ratio > 1, like the Nexus
> >One with its penTile display
> >http://en.wikipedia.org/wiki/Nexus_One#Hardware
> >or the iPhone 4.
> >Is your test setup publicly accessible?
> 
> It is now, here:
> 
> http://mull.geofabrik.de/hires.html
> 
> By default this will come up with standard Mapnik tiles from
> osm.org, but you can switch to my hires tiles in the layer switcher.
> If I do this in Firefox on my desktop machine, there's hardly any
> difference between the two, as OL downscales the images from 512x512
> to 256x256 for display. Only if you right-click on an image will you
> see that it is indeed bigger than normal.
> 
> I'd be interested in hearing from users of high-resolution displays
> if these big tiles actually make a difference (except being slower
> to load...).

With your page on e.g. an iPhone, the two sets of tiles look identical,
but that’s because its a huge page squeezed onto the tiny display, so
even the standard tiles have far too high resolution.
And one cannot zoom into the page as the gesture is caught by openlayers
for zooming into the map.

But I’ve copied your page, adjusted the style and tiles URIs and added a
viewport.
As expected, it doesn’t make any visible difference on an iPhone 3
(pixel ratio 1), but the difference is remarkable on e.g. an HTC Sensation
(pixel ratio 1.5) or an iPhone 4 (pixel ratio 2).

See https://mlist.timesink.de/osm-geofabrik-highres/ for some screen
shots.

rj