Abstract: A method for removing hidden lines in a two-dimensional surface chart disclosing an image of a three-dimensional surface, includes storing the X, Y and Z co-ordinates of selected points (A, B, C, D, E) of the surface as a first matrix, transforming the first matrix into a second matrix indicating the drawing sequence through the selected points, rotating the points of the second matrix around the Z-axis a first angle .alpha., rotating the second matrix points a second angle .beta. and drawing the two-dimensional surface chart in accordance with the indicated sequence using the X and Y co-ordinate values of the rotated points. The drawing sequence comprises a drawing operation of X-traces, an X-trace being defined as a line passing through points having substantially the same Y values in the first matrix, the drawing operation of one X-trace being followed by a plurality of .DELTA.