[mapguide-internals] RFC required for tile caching changes?

Chris Claydon chris.claydon at autodesk.com
Fri Jan 12 15:24:01 EST 2007


A sample tile location would be as follows:

 

......\ Repositories\TileCache\Samples_Sheboygan_Maps_Sheboygan\7\Base
Layer Group\R2\C3\3_4.png

 

The R and C indices correspond to rows and columns where each row
contains 30 tiles vertically and each column contains 30 tiles
horizontally.

 

This indicates that:

 

1)       We're at zoom level 7

2)       We're in grouped row 2

3)       We're in grouped column 3

4)       The tile location within this grouped row/column combination is
(3,4).

 

The R and C indices never take a zero value (to avoid issues with
negative values around the origin), so this tile corresponds to a
location of (33, 64) in the old scheme.

 

I took a quick look at the Tile Map Service Specification, but it
doesn't appear to support the concept of grouping blocks of tiles into
subfolders in its current form. Can you provide more information on
whether this is possible?

 

Chris.

 

  _____  

From: mapguide-internals-bounces at lists.osgeo.org
[mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Chris
Claydon
Sent: January 12, 2007 12:47 PM
To: MapGuide Internals Mail List
Subject: RE: [mapguide-internals] RFC required for tile caching changes?

 

A barrel of worms!

 

  _____  

From: mapguide-internals-bounces at lists.osgeo.org
[mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Jason
Birch
Sent: January 12, 2007 12:41 PM
To: MapGuide Internals Mail List
Subject: RE: [mapguide-internals] RFC required for tile caching changes?

 

If you're going to change the storage schema, how much work would it be
to align it with the TMS specification?

 

http://wiki.osgeo.org/index.php/Tile_Map_Service_Specification
<http://wiki.osgeo.org/index.php/Tile_Map_Service_Specification> 

 

Feel like you've opened a can of worms Chris?

 

Jason

 

  _____  

From: mapguide-internals-bounces at lists.osgeo.org on behalf of Chris
Claydon
Sent: Fri 2007-01-12 10:39 AM
To: MapGuide Internals Mail List
Subject: [mapguide-internals] RFC required for tile caching changes?

We have found that problems can occur if too many cached tile images are
stored in a single folder on the hard drive. For this reason, I have
some changes to submit that ensure that we only store 900 tiles per
folder (in 30 x 30 blocks).

This changes the locations of stored tiles, by introducing new
subfolders, and will thus "orphan" any tiles already created by the
cache. Since the root folder for the tiles for any given map will not
change, these orphaned tiles will be cleaned up if the user modifies the
map definition or makes a call to the Clear(MgMap* map) method in the
tile service API. The user could also force the cleanup simply by
deleting the contents of the root cache folder when they upgrade to the
version containing these changes.

I'd like to treat this submission as a simple defect fix, but the
requirement for the extra cleanup steps may indicate that an RFC is
required, and I'd like to know the opinions of the PSC on this matter.

Also, please let me know if you require any further information about
this submission.

Cheers,

Chris Claydon.

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