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Overview
iShare returns results based upon a location - whether that be a click on a map or a given address in My House. If you imagine that a point click equates to a small bounding box on the earth's surface then tolerance is the measure by which we can expand that bounding box.
iShare Maps / GIS Pixel Tolerance
Info Click results are returned based upon the following: when a user clicks on a map we know the pixel that they click on and, based upon the Map Pixel Tolerance and the Scale, we calculate a bounding box from which the Info click results are determined.In the iShare Settings they are actually selecting an individual pixel. iShare takes that pixel and with a Scale a bounding box is calculated. Any geometries found to overlap with this bounding box are returned as results. Unfortunately for point layers we might not click on the exact pixel that covers the point's geometry. For example a layer may be rendered with a 20px symbol image for each point object. The symbol is anchored to the point's geometry by the image's mid-point by default. This means that if a user doesn't click on the exact centre of the symbol they will not hit the actual geometry of the object. In order to correct this a map pixel tolerance is set which widens the bounding box to cover the physical area that the symbol represents.
Check that the iShare Settings for MapPixelTolerance is reasonable. Open Studio and select Settings, on the General Settings tab scroll down until you see the Web entries. Here you will see the MapPixelTolerance setting. This is entered as pixels and these get converted into co-ordinates based around the point clicked on the map. This will be scale dependant upon the current Zoom levelthe number of pixels the bounding box is calculated to cover at any one scale.
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The MapPixelTolerance should NEVER never be set to less than 10 pixels otherwise clicking on and probably no more than 20. Lower than 10 and Point symbols will may not return results. Higher than 20 and the bounding box used becomes too large and more results are returned than expected. The value is dependent upon the size of the rendered symbols used and the anchor position for the each point layer. The majority of points will use a mid-point anchor with a symbol image normally no bigger than 20 pixels. In that case '10' would be an appropriate value to use. Unfortunately there is a danger when clicking close to Polygon boundaries more results than desired may be returned. This is something that we are looking to resolve in future versions. |
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