Clarify getLegendData when using opacity

It is common to use opacity & ramp and then trying to build a legend. But that can lead to an error, as it is described in this conversation between @ramiroaznar and @elenatorro:

• User: I am strugging to make getLengendData() work --> viz.color.getLegendData throws ‘getLegendData is not a function’

getLegendData works for ramps, if not, you’d have to use value

• User: the expression was opacity(ramp(linear($valor, @min, @max), sunsetdark), 0.5)

If it’s inside an opacity, you have to assign the ramp expression to a variable, like this: @myRamp: ramp(linear($valor, @min, @max), sunsetdark), 0.5) and then: opacity(@myRamp) so you can access the ramp through the variable viz.variables.myRamp.getLegendData().

So it would be nice to add this explanation / example to the legends guide somehow

[makella]

to update, we are in the final steps of adding legend and widget examples to the dev center. we have included steps in the Guide for opacity and also have the same example available in the examples/legend section.

[makella]

ahhhh, ok! i’ll try this out.

yes, could get the transparency in the map but not the legend which is what i was after. thank you!!