This enumeration determines the unit of measure for all quantities.

Values:

IG_TW_UN_CENTIMETERS	Centimeters
IG_TW_UN_INCHES	Inches
IG_TW_UN_PICAS	Picas
IG_TW_UN_PIXELS	Pixels
IG_TW_UN_POINTS	Points
IG_TW_UN_TWIPS	Twips