[OpenLayers-Dev] singleTile optimization

Stephen Woodbridge woodbri at swoodbridge.com
Fri Oct 5 11:31:19 EDT 2007


Thanks for the more detailed explanation of your use case.

Paul Spencer wrote:
> On 4-Oct-07, at 10:04 PM, Stephen Woodbridge wrote:
> snip ...
>> OR that the single tile is always rounded up so that the off screen
>> corners snap to a tile vertices, but it is centered on the appropriate
>> point in the viewport.
>> Think of it as a single tile with a buffer, but the buffer is always
>> snapped to the nearest tile vertex that is off screen. This just makes
>> the image somewhat more cache-able at the expense of larger images. and
>> you could slide the image up to the buffer edge without requesting a new
>>   image.
>> I am not suggesting that we do this, only that it is another
>> interpretation of Pauls request.
>> The other reason that people might want to run singleTile models is that
>> they do not want the overhead of setting up a tilecache and managing it.
>> For example, I do a lot of small low volume pages that do not need
>> tiles, it would just needlessly complicate things.
> Stephen,
> right now, the singleTile implementation defaults to a ratio of 1.5, 
> which means that a singleTile draw is 1.5 times larger than the 
> viewport.  In many cases, people use large viewports because it is cheap 
> with tiles.  The default singleTile will then draw a tile much larger 
> than the loaded grid.  I don't think that larger images is actually the 
> issue here.

Right. I usually set ratio: 1

> Also note that if you use singleTile instead of tiles, you are using a 
> singleTile as the baseLayer and then there is no convenient grid to snap 
> to.  My original contention was that this was only useful when 
> singleTile is not a baseLayer AND the baseLayer is not singleTile.  I 
> suppose it would be possible to deterministically size/place the 
> singleTile such that it behaved more like a tiled layer but that was not 
> my use case.

Ahh, gotcha. I had the random thought that if the grid was defined as 
say 256x256 pixel tiles the the "extended" singleTile would get rounded 
up to that grid intervals. Like if you needed 4 tiles to fill the 
viewport then the single tile would be the size of the 4 tiles glued 
into a single tile. This would make the single tiles some what more 
cache able because they would always get round to the 256 values. But 
like I said, I'm not advocating it, it was just a random thought 
triggered by the discussion.

Best regards,

> Just to elaborate a little more, here is my use case:
> 1) user is able to create a dynamic overlay by searching a database of 
> points - could be anything but in my case it is real estate locations
> 2) user can specify a wide range of criteria to filter the locations
> 3) user can change the criteria at any time
> 4) user can view all available results at any available resolution
> 5) there can be upwards of 50,000 results to display at any one time
> 6) new locations are added dynamically in the back end at any time, but 
> they do not need to be included in the 'current' query.
> 7) typical coverage for a user is an entire US state
> We can't conveniently tile every query, even dynamic tiling takes too 
> long and would have too short a useful life span (i.e. the tiles may or 
> may not get used again.)  The number of options make it unlikely that we 
> could share tiles between users at any given point in time.  And dynamic 
> tiling requires administrative stuff to clean up because disk space is 
> not unlimited.
> Perhaps a somewhat esoteric use case ... anyways, not much of an issue.  
> I only originally wanted to know if folks had thought of it, and if not, 
> would it be a generally useful idea.  I'm getting the sense that there 
> is some differences of opinion in how useful it will be.  Fortunately, 
> Chris is so tied up in vector stuff that I can probably slip the change 
> by him ;)
> Cheers
> Paul
> +-----------------------------------------------------------------+
> |Paul Spencer                          pspencer at dmsolutions.ca    |
> +-----------------------------------------------------------------+
> |Chief Technology Officer                                         |
> |DM Solutions Group Inc                http://www.dmsolutions.ca/ |
> +-----------------------------------------------------------------+

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