added re-initialization of weights attribute to ensure results of subsequent calls do not accumulate.
added re-initialization of weights attribute to ensure results of subsequent calls do not accumulate.

--HG--
branch : feature/tp/kriging

heistermann/wradlib,kmuehlbauer/wradlib,wradlib/wradlib,wradlib/wradlib,kmuehlbauer/wradlib,heistermann/wradlib