[OpenLayers-Dev] OpenLayers for Mobile devices

Bob Basques Bob.Basques at ci.stpaul.mn.us
Mon Dec 27 11:23:33 EST 2010


I think the general idea that Beau is describing is "No white screen"!!  Always hate a blank screen when transistioning a map, especially when zooming.  Even something wildly pixelated is valuable to the end user to key on reference points, it also allows for rapid transitioning without waiting for the final rendering of things. 

Using a wheel zoom on this interface would be my example of how zooming should work visually: http://gis.ci.stpaul.mn.us/gis/gismo_public/html/, this could use possibly more transistion steps as well as better end loop control, as in I should be able to pan, while waiting for the new tiles to download and replace the previously rescaled tiles.  Right now the user needs to wait for the new tiles to display before rezooming or panning.   This interface has been in use for a number of years (before OpenLayers even . . .) and is a preferred transistion effect.  We've done some smaller implementations of OpenLayers from time to time, and the "always on" Map Feature is usually brought up at some point as a desirable feature, this is especially important in a emergency response/preparedness situation. 


>>> Beau Anderson <elbeau at gmail.com> wrote:

No, the "resize" behavior is not the same as what I am describing. Using Google maps as an example, as you pinch to zoom in/out the raster image tiles resize to sized in-between the zoom levels. The "resize" transitionEffect does do a raster resize, but only to an actual zoom level. In other words, there is no graceful zooming to fractional zoom levels. In order to get an effect similar to Google's, you need to not only make the background tiles zoom to fractional zoom levels, but the actual foreground tiles themselves need to do the same, because if you've pinched to zoom in to a fractional zoom level, you need any newly loaded tiles to also be resized appropriately. 

To put it another way, if you're loading tiles whose actual dimensions are 256X256 pixels, it doesn't mean that you will actually be displaying the image at 256X256. The fractional zooming is second-nature for users on iOS and the newer versions of Android mobile devices these days. The other benefit you get for desktop computer users is that once you have fractional zooming, then even if the're doing a zoom to a new zoom level, it's not hard to do an animated zoom-in/zoom-out (again, the same way Google does). In the end, OpenLayers is AWESOME in it's support for various formats, but there are a couple UI paradigms that I really want to tweak before I turn it loose on my user base. The thing I HAVEN'T delved into yet is how easy/hard this will be to implement on other types of layers so that the whole UI acts appropriately :s 

On Sun, Dec 26, 2010 at 6:13 AM, Tom Hughes <tom at compton.nu> wrote:

On 23 December 2010 17:21, Beau Anderson <elbeau at gmail.com> wrote:

I've got an existing successful iPhone application that I'm porting to other platforms. There's a lot that I want to add to my app's mapping functionality and OpenLayers looks like it would fit the bill great, but the user experience is just not as smooth as Google and Bing provide. The headache that I've been working on is getting layers that extend from OpenLayers.Grid to act more like Google where when you zoom in or out it simply scales the tiles you already have loaded then loads new tiles on top of them. To accomplish this we need to rethink the way that Grid layers layout their tiles so that there are multiple layers of tiles within one Grid (not just foreground and background img's in Image.js).

Doesn't setting transitionEffect to "resize" on the layer already do that?


Tom Hughes (tom at compton.nu)

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