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I am testing an application this is developed in OpenLayers 2.13 with Chrome, and I am using MapServer as the map provider.

I have noticed some tiles occasionally does not render, when I pan/zoom the map. There is no specific way to recreate this problem on my application, the missing tiles are random. But I can say that the problem is common enough for most users to notice.

MapServer is running on an dedicated core i7 desktop with 16GB of RAM. I do not understand if it is a hardware issue, software issue, or load handling issue.

I have found some links that specifies the solution to hide the pink image XYZ Layer in OpenLayers has missing tiles

But I am interested to know what is the cause of missing tiles? What are the possible factors causing missing tiles.

UPDATE

Sometimes it will also appear that the tiles are loaded or what appear to be loaded correctly, turned from map tiles into blank tiles.

  • Can you use a tool like Chrome developer tools or Firebug to examine the network requests? It is likely/possible that one of the tiles has failed, and the error message may give a clue. Improving network performance shows how to monitor the resources as they load – Stephen Lead Jan 22 '15 at 2:45
  • Hi Stephen, I have tried to monitor the chrome developer tool > network, there is no error on a failed request. All requests return Status 200. But the tiles will just remain missing. – kytay Jan 22 '15 at 2:57
  • @StephenLead I did the same monitoring for firefox, it gives the same result, all request returns Status 200, but there is a missing tile on firefox. – kytay Jan 22 '15 at 3:15
  • Dumb question but do the missing tiles definitely exist? Is it always the same tiles which fail? Can you test them in a non-Open Layers map or desktop app (I'm not a MapServer user so I don't know the options, sorry) – Stephen Lead Jan 22 '15 at 3:35
  • @StephenLead Hi it's not a dumb question. :-) I have tried to check those possibilities too, but it is very difficult to identify. (1) it is not always the same tile that is missing, (2) it usually is one tile, or if more tiles, it will be a clustered of tiles, (3) I cannot test with other non-openlayer web map tool like leaflet, because they do not have native support for MapServer. – kytay Jan 22 '15 at 5:33
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In Firefox you could do a rightclick on the blank tile and choose "open image in New tab" to see if it is displayed outside your app. Apart from that you could try this to see if there is an image load error: OpenLayers.Util.onImageLoadError = function() {console.log("error");}; 

or use the CSS-Class:

.olImageLoadError { /* when OL get's a Error 404 mark the tile with a red border */ border:3px solid red; }

for testing purposes you could just load your layer into QGIS and test if there are also tiles missing

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