I'm searching for a possibility to calculate landscape metric "shape index" in the field calculator?
Shape index = 1 when the patch is circular and increases without limit as the patch becomes more irregular.
like a perimeter/area ratio?
there are loads of metrics, most of which can't be done in the field calculator since they entail such things as convex hull, minimum area bounding rectangle ratios.
You might want to streamline your criteria to the most suited for your circumstance rather than impose a field calculator solution
Yes like a perimeter/area ratio. I would like to differentiate between compact features I want to preserve and slivers I want to delete after the use of a geoprocessing tool?