[Qgis-user] QgsDistanceArea() confusion

[Pal Schmitt]

Dear All,
I am trying to write a plugin but am somewhat lost when it comes to
using the QgsDistanceArea() class.
Assume I have two layers, layerA and layerB in arbitrary CRS.
What is an idiot-proof way of using 

d = QgsDistanceArea()
and
dist=d.measureLine(featurefromlayerA,featurefromlayerB)

but always obtain the distance dist in meters?
The gui measurement tool seems to work for me, but the above code seems
to give good results only if both features/layers are transformed to

layer.crs().projectionAcronym()
u'utm'
layer.crs().geographicCRSAuthId()
u'EPSG:4326'
which seems a bit clumsy...
Thanks for any help,
Pal