Sizes not always Pixels

[1Map]

Although you handle your style sizes as Pixels, that may not always be the case, for example the following means that the font size is 2 meters, not 2 pixels:

          <sld:TextSymbolizer uom="http://www.opengeospatial.org/se/units/metre">
            <sld:Label>
              <ogc:PropertyName>unitno</ogc:PropertyName>
            </sld:Label>
            <sld:Font>
              <sld:CssParameter name="font-family">Arial</sld:CssParameter>
              <sld:CssParameter name="font-size">2</sld:CssParameter>
              <sld:CssParameter name="font-style">normal</sld:CssParameter>
              <sld:CssParameter name="font-weight">normal</sld:CssParameter>
            </sld:Font>
            <sld:LabelPlacement>
              <sld:PointPlacement>
                <sld:AnchorPoint>
                  <sld:AnchorPointX>
                    <ogc:Literal>0.5</ogc:Literal>
                  </sld:AnchorPointX>
                  <sld:AnchorPointY>
                    <ogc:Literal>0.5</ogc:Literal>
                  </sld:AnchorPointY>
                </sld:AnchorPoint>
              </sld:PointPlacement>
            </sld:LabelPlacement>
            <sld:Halo>
              <sld:Radius>
                <ogc:Literal>0.5</ogc:Literal>
              </sld:Radius>
              <sld:Fill>
                <sld:CssParameter name="fill">#FFFFFF</sld:CssParameter>
                <sld:CssParameter name="fill-opacity">0.8</sld:CssParameter>
              </sld:Fill>
            </sld:Halo>
            <sld:Fill>
              <sld:CssParameter name="fill">#000000</sld:CssParameter>
            </sld:Fill>
            <sld:VendorOption name="maxDisplacement">10</sld:VendorOption>
            <sld:VendorOption name="spaceAround">0</sld:VendorOption>
            <sld:VendorOption name="group">false</sld:VendorOption>
            <sld:VendorOption name="repeat">0</sld:VendorOption>
            <sld:VendorOption name="partials">true</sld:VendorOption>
            <sld:VendorOption name="goodnessOfFit">1</sld:VendorOption>
          </sld:TextSymbolizer>

Also the same with PolygonSymbolizer, LineSymbolizer, etc...

[Razi91]

https://stackoverflow.com/questions/34483178/openlayers-draw-line-string-with-line-width-in-meters
It would require passing ol/Map styler.

[1Map]

Yes,

Note: the Unit-of-Measure in the SLD

uom="http://www.opengeospatial.org/se/units/metre"

[ajkopinga]

It's technically possible to support non-pixel uom on a symbolizer, but also a lot of work.

The style function recycles OpenLayers style objects with static properties (like a line symbolizer that's always 4px wide). But when you start using meters for instance, all dimension-related symbolizer properties will have to be dynamically modified at each zoom (and possibly pan) of the map.

Furthermore, according to the SLD spec you can override any uom set on the symbolizer by appending 'px' to a property (like '5px'). This means that units of measure can be mixed within a symbolizer, which in turn means that all numeric symbolizer properties relating to dimension should keep track of their own units of measure.