File format:
model size:40598 81398; maximum (x,y) of the model.
volume index:0 ; the index of volumes
layer index:0 ; the index of layer in current volume
part index:0 ; the index of part in current layer
outline index:0 ; the index of outline in current part
x0 y0 x1 y1 x2 y2; Start to output list of point (x,y) of the 1st polygon
x0 y0 x1 y1 x2 y2 x3 y3; 2nd polygon
...
The unit of coordinate is 1000th of millimeter.