wmsplugin: blank tiles saved

[Teemu Koskinen <teemu.koskinen@…>]

Sometimes WMS-server (at least Landsat) returns blank tiles and not an error message. wmsplugin thinks these are valid and happily saves them to cache. These tiles seem to be around 800 bytes, much smaller than proper tiles returned by the server.

The wms-layers reload erroneus tiles action does not reload these tiles, as the plugin doesn't recognise blank tiles as errnoeus.

[anonymous]

I have this problem since yesterday. I can't really use landsat images anymore because it loads only half the tiles or less

[anonymous]

Example of blank tile.

[anonymous]

Hi,

I've been having this problem since last week, both on my home machine (Debian Linux, ADSL to internet) and at work (WinXP via work network and proxy). It has stopped me from doing any WMS mapping. I keep JOSM and plugins updated on both machines.

As with the other reports, about half tiles are blank, and only about 800 bytes per tile in cache. Most are 806 bytes, a few are 804 bytes.

Deleting the blank tiles and reloading doesn't help.

Thanks.

[xeen]

Detecting them based on file size surely isn't the right approach. I did a bit testing and I sometimes get tiles consisting of only one color but still are like 2 kB. Does anyone know a good algorithm to do that?

[anonymous]

Replying to xeen:

Detecting them based on file size surely isn't the right approach. I did a bit testing and I sometimes get tiles consisting of only one color but still are like 2 kB. Does anyone know a good algorithm to do that?

All of mine are 804 or 806 bytes. JOSM shows them as black in colour.

I had a look at some of the blank tiles with a hex editor, and between the header and end of file stuff, the rest of the data shows as all zeros. Perhaps an algorithm/short_script to examine the data area of the files and check for all zeros?

Just a thought.

[stoecker]

​[o15091].

[alexm]

The threshold of 2048 is to small, I raised this to 4096 in the patch for #3294

[alexm]

This is for example for error messages of the Yahoo WMS plugin.

[stoecker]

Closed as duplicate of #3591.