overrideDefaultWeight(float w, bool isFixed)
This method sets the current default line weight to w. If isFixed is FALSE, the line weight is taken to be millimeters on the surface of the Earth. This means the line will thicken as the user zooms in. Otherwise, the line weight is taken to be pixels relative to the view. This means the thickness will remain constant as the user zooms in.
The initial default line weight is w=0, isFixed = TRUE, which produces a fixed-weight line of minimal thickness.
The method returns 0 upon success, and an error code if w is invalid.