[OpenLayers-Dev] Should ArcGISCache getURL "this.getResolution()" be "this.map.getResolution()" instead?

myOpenLayersUName joanne.mcgraw at SYMPATICO.CA
Fri Mar 2 14:37:32 EST 2012


I'm hoping someone more knowledgeable in OpenLayers code can review this
post and tell me if I am correct in my proposed fix and whether what I have
observed is actually a bug or just the result of a misunderstanding on my

I have an OpenLayers.Map with 3 resolutions available (e.g., resolutions =
[1000,100, 10]). I have an ArcGISCache layer in the map that I only want
available for display at the 100 and 10 resolutions (that is, it will show
greyed out in the LayerSwitcher at 1000 and not be displayed in the map).
When the user zooms in to the 100 resolution on the map (resolution 100 is
in index 1 of the baselayer's resolution array), the current
OpenLayers.Layer.ArcGISCache class' getURL method's first line of code ends
up with the value of 10 (rather than 100) in the "res" variable because that
is the item at index 1 in its own list of resolutions. Consequently, the
method's algorithm generates invalid paths to the tiles in the cache.

Originally, I started looked into the OpenLayers.Layer class' getResolution
method. It seems to assume the map (or more specifically, the map's
baselayer) and the layer in question at any given time will always have the
same number of resolutions. That didn't seem like a safe assumption to me
but I looked back through the history of the code and see that that method
has been that way for years. So, I went looking around throughout OpenLayers
and find that the OpenLayers.Layer's getResolution method is only used a
handful of times (Grid and KaMap's getTileBounds and Image's resetBackBuffer
and startTransition). This leads me to believe that the OpenLayers.Layer's
getResolution method is more specific in its usage than I expect. 

Given that thought, I'm now thinking instead that the problem is just with
the OpenLayers.Layer.ArcGISCache getURL method. Changing the use of the
Layer's getResolution method might have farther reaching impacts than I
could guess at. And, most other places in OpenLayers where a getResolution
call is made, they are made to the map...as I am proposing doing.

So, I have fixed my problem by changing the first line in the
OpenLayers.Layer.ArcGISCache class method getURL to (the commented section
at the end is the existing line of code): 

Could someone give me an idea if this is an acceptable approach? And, if so,
would you consider it a bug that I should log?

Oh, I am using ArcGIS Server 10.0 and OpenLayers 2.11.


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