Geoserver's scale values corresponds to OL's zoom levels

Question

I have a PostGIS table that contains geometry, min_scale, and max_scale fields. The PostGIS table is published as a Geoserver layer with EPSG = 4326. I have created a CSS Style Doc that will show each geoemtry only in its scale range; something like:

[@sd <= max_scale] [@sd >= min_scale]{
     mark: symbol(circle); 
}

My problem is how to set the min_scale and max_scale fields to work properly with Openlayers zoom levels. I tried to use the scale values from the EPSG:4326 Gridset:

http://localhost:8080/geoserver/web/wicket/bookmarkable/org.geoserver.gwc.web.gridset.GridSetEditPage?6&gridSet=EPSG:4326

But it didn't work properly; for example if I set

min_scale = 545978 which corresponds to zoom 9

max_scale = 2183915 which corresponds to zoom 7

The feature appears only at zoom 7 and 8, and didn't appear at zoom 9.

I also tried the values at this table (Default Gridset):

https://docs.geoserver.org/latest/en/user/styling/ysld/reference/scalezoom.html#default-gridset But the same problem occurred.

My question is what is my problem? which scale values should I use in order to work properly with Openlayers zoom levels?

@IanTurton I didn't understand your question. I don't have any DPI settings in OL. — Faz B, Dec 08 '18 at 12:48
because scale is the ratio between pixels and real world units — Ian Turton, Dec 09 '18 at 10:40
Thanks @IanTurton for the information, could you please provide us the standard Scale calculation formula/method for OL? — abd0991, Dec 09 '18 at 10:46

score 1 · Answer 1 · answered Dec 09 '18 at 11:57

As discussed in this question GeoServer uses a DPI (or more correctly a Pixels per inch) of 90.714. Meanwhile this question suggests that OpenLayers uses 72. This is why you get a miss match in scales. The easy answer used to be you added an OpenLayers.DOTS_PER_INCH variable. I don't know how OL3+ handles it.

Geoserver's scale values corresponds to OL's zoom levels

1 Answers1