[OpenLayers-Dev] singleTile optimization

Paul Spencer pspencer at dmsolutions.ca
Wed Oct 3 22:04:34 EDT 2007

I guess I missed the original discussion or don't remember it.  I can  
see that there are some issues with how this might be implemented.   
For instance, it only makes sense to attempt this for singleTile  
layers that are not also a baseLayer AND if the baseLayer is not a  
singleTile layer.  Otherwise there is no grid to synchronize the  
extents with.

The reason I was asking is because we had implemented the singleTile  
concept in kaMap for a particular use case and it was aligned with  
the 'meta extent' of the currently loaded tiles.  The meta extent are  
the extent of all loaded tiles in the base layer.  The singleTile was  
redrawn when either a row or column of tiles was wrapped, rather than  
when an edge of the singleTile was inside the current viewport extent.

The default in kaMap was to use a single tile buffer rather than a  
two tile buffer, so the singleTile render would be roughly the same  
size as the current OpenLayers singleTile ratio of 1.5

The potential performance gain is largely theoretical to me since I  
always run my browser with the cache turned off.  However, as we are  
moving one particular client from kaMap to OpenLayers, they have  
noticed a difference.

Chris, can you elaborate on why you are/were against this?


On 3-Oct-07, at 6:13 PM, Erik Uzureau wrote:

> Wait. didn't we have this discussion before? maybe i'm confused.
> I feel like we determined that this actually wouldn't work¿
> someone better than me at logs....
> E
> On 10/3/07, Trond Michelsen <trondmm-openlayers at crusaders.no> wrote:
>> On Wed, Oct 03, 2007 at 05:00:32PM -0500, Erik Uzureau wrote:
>>> On 10/3/07, Christopher Schmidt <crschmidt at metacarta.com> wrote:
>>>> On Wed, Oct 03, 2007 at 09:50:49PM +0000,  
>>>> pspencer at dmsolutions.ca wrote:
>>>>> What do you think about aligning singleTile bounds to the grid to
>>>>> promote cacheability in the client?
>>>> I think this has come up before, and I've been against it, but I  
>>>> don't
>>>> use singleTile, so it's not really my call.
>>> Seems like a reasonable idea in theory, but you're going to have to
>>> have some big ratios.. no?
>> Sure, but I'm convinced it'll be a lot better than no caching
>> whatsoever. Especially if there's no temporal data, and the maps can
>> be cached indefinately.
>> --
>> Trond Michelsen
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|Paul Spencer                          pspencer at dmsolutions.ca    |
|Chief Technology Officer                                         |
|DM Solutions Group Inc                http://www.dmsolutions.ca/ |

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