[Tilecache] throwing out bad tiles

[Michael Anderson]

Thanks for the response Matt. Building the entire cache would take > 1 TB with a reasonable number of levels, and that's not possible at the moment. If I could do that, I could have a script remove the bad ones and rerun without -f and eventually have all good tiles.

In playing with it more I am getting empty tiles fairly regularly. The remote server is ArcIMS and it is either occasionally returning the white tiles, or it is returning no tile and TileCache is creating them. Still not sure which it is. As I said in the original post, I've see it randomly not return an image before, but never a white one that I can remember.

So what I need is to automatically delete the bad ones as they are generated so the user won't keep getting the cached white ones. I'm thinking I can use .Net's FileWatcher to detect when an image is added, see if it's too small to contain an image, and delete it. If I can't think of anything better by Monday I'll give it a shot.

Mike



From: mattxbart at gmail.com
To: m_anderson14 at hotmail.com
Subject: Re: [Tilecache] throwing out bad tiles
Date: Fri, 20 Mar 2009 11:20:11 -0700

I would use tilecache_seed.py with the -f (available in trunk) option to overwrite the bad tiles for the bbox and zoom level in question. Then I would probably pre-seed the whole cache for good measure if you have the space and resources.
-matt
On Mar 20, 2009, at 9:17 AM, Michael Anderson <m_anderson14 at hotmail.com> wrote:


Hello,

Just started with TileCache today. I'm caching images coming from a WMS service that I have no control over. I got it set up with the extent and resolutions I need, edited index.html to point my cache, and it works great. As I was playing with it, it generated some empty tiles - just a white background.

My first question is, did the remote server return the white images or did it return no image and TileCache made the empty ones. I've used this service for a while and have gotten random errors occasionally that return no image, but I can't remember seeing white images before

My second question is, now I have cached tiles with no imagery. I assume I can manually delete them, zoom to the area again, and it will load new tiles - hopefully with imagery this time. 

The empty images are only 2KB, so I'm thinking I can use that to determine whether a tile has anything in it. Before I try anything I was wondering if anyone has come up with an automated way to throw out bad tiles? 

Thanks.

Mike Anderson

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