I've been trying the GeoServer Rendering Transformations - Point Stacker. According to this docs there's an optional cellSize parameter for setting the "Size of the cells in which to aggregate points, in pixels, default = 1".

I made the SLD based on the SLD example in the above OpenGeo docs.

I tried 2 cellSize (30 and 150). Here are the results:

Blue squares are points (exact, not clustered). Orange circles are clusters. Both layers (blue squares & orange circles) are WMS.

There are 41 points in the island.

Now the question: The Graphic circles (defined in SLD as <PointSymbolizer>) seems to be positioned incorrectly. The above pictures show that displacement grow with cellSize parameter.

Why does this happen? Please advise.

heaps of thanks.

I'm using:

• GeoServer 2.7.0 on Apache Tomcat 7.0.61 on Windows Server 2008 R2 Datacenter 64-bit on VMWare
• JVM: Oracle Corporation: 1.7.0_80 (Java HotSpot(TM) 64-Bit Server VM)
• OpenLayers 2.12
• PostGIS - PostgreSQL 9.4.1 (on Windows Server 2008 R2 Datacenter 64-bit on VMWare)

By the way, I reckon other question asking about random position of PointStacker, but no solid answer so far.

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Edited, added more facts.

The below picture shows the same points (of another area). Again the blue squares are points (exact, not clustered) & orange circles are clusters.

Now because the zoom level is very high (more zoom in than previous picture), the 4 points are not clustered. Ideally the orange points should be rendered in exact position as the blue point layer. But apparently GeoServer renders the orange points with some displacement. This is also asked in this question.

This picture also shows that displacement grow with cellSize parameter. Interesting enough that the displacements seem to be random.