CIGAL Reference Manual, Chapter 2 (Commands): REDRAW
usage: redraw [ vv eraseflag measureflag]
REDRAW regenerates the vector display image. The default action of REDRAW is to erase the display and then redraw all of the active vectors in the internal vector variable VECS. This is particularly useful if you change the display attributes (SCALE(2), OFFSET(2), or ROTATE(2)) because REDRAW uses the current transformation settings to draw each vector.
REDRAW can also be used to regenerate just part of the active vector list in VECS, or to display a list of vectors that is not part of the VECS variable. Selecting which vectors to draw is controlled by the 1st argument (VV). The VV argument can be a number, in which case it is the number of the first vector in VECS to draw, with drawing continuing until the end of VECS. (The length of VECS is stored in the internal variable NVECS.) Alternatively, VV can be a vector list variable (or subset of a variable), in which case all of the specified vectors are redrawn.
The arguments to REDRAW specify which part of vecs to redraw:
FIRSTVEC is the number of the first vector to draw (default = 0). NUMVECS is how many vectors to draw (default = nvecs - FIRSTVEC). ERASEFLAG indicates whether the display should be cleared before beginning to redraw. The default is 1 (i.e., erase) when all vectors are being redrawn (FIRSTVEC = 0 and NUMVECS = nvecs), otherwise the display is not erased.