I have an xyz file that I want to convert negative field values in the z column to positive values. How do I do this with field calculator?
In QGIS you can use
abs("fieldname") to turn them into always positive values.
In ArcGIS desktop you could use the following python script in the field calculator, where you would create a new field (say, FIELDNAME2) and calculate the following (where FIELDNAME1 is your original values):
def values(n): if n < 0: return n * -1 else: return n