Offset Y for Textsymbolizer needs to be negated

[KaiVolland]

Bug

The geostyler-style and SLD handle the Y value of the offset/displacement contrary.

SLD: A value of 20 in SLD means 20 pixel above the acutal position
geostyler-style: A value of 20 means 20 pixel below the actual position

Expected behavior

The visual output should be more or less the same.

To fix

The Y values of the offset/displacement have to be negated when parsing.

Additional context

Bug found by @yang6626 here geostyler/geostyler-openlayers-parser#432

[jansule]

I'm not sure this should be seen as bug.

According to their specifications:

• SLD/SE shifts texts with a positive offsetX value upwards (see SE implementation specification section 11.3.2)
• OpenLayers shifts texts with a positive offsetX downwards (see https://openlayers.org/en/latest/apidoc/module-ol_style_Text-Text.html)

If we keep following the pattern of leaving interpretation of styling to the respective rendering engines, everything works as expected right now.

[KaiVolland]

We actually do want to have the appearance to be mostly the same don't we? The geostyler-style documentation is also clear about how the value is interpreted. So why not negate the value when reading and writing the value?

[KaiVolland]

@jansule we might want to have a look at this again. Maybe with the geostyler converter demo?