Image service - what scale is source data accessed?

08-05-2010 08:21 PM
Occasional Contributor
Hi.  Is it possible to tell at what scale when the user no longer sees service overviews and is viewing the source images (i.e. full resolution data)?  Is there something in the service definition that indicates or controls this?

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Esri Regular Contributor
There is a direct relation between pixel size and map scale.

ScaleFactor = Cell Size x 96/0.0254
Therefore, if the scale is 1:20,000, the cell size is 5.29 meters.

Cell Size = ScaleFactor x 0.0254/96
Therefore, if the cell size is 5 meters, the scale is 1:18,898.

The scale at which the overviews will be displayed is the MinPS value of the Service overviews * 96/0.0254. (Since the base imagery take priority, it is actually more correct to use the MaxPS of the base imagery, but this is generally set the same as the minPS of the overviews)

Note that overviews need not have the same scale at all locations. If the resolution of the base imagery varies then the minPS of the overviews may also be different in different areas.
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