moved INVALID_ELEVATION to HeightField.h
moved INVALID_ELEVATION to HeightField.h

markraz/vtp,nakijun/vtp,markraz/vtp,markraz/vtp,nakijun/vtp,seanisom/vtp,seanisom/vtp,seanisom/vtp,seanisom/vtp,nakijun/vtp,markraz/vtp,nakijun/vtp,markraz/vtp,seanisom/vtp,nakijun/vtp