Abstract: To measure the waviness of aircraft surface accurately and efficiently, an improved algorithm
for the projection of points on parameter-curved surface is proposed. The point projection on curved
surfaces is calculated by adopting the approach of elliptical torus patch approximation. Firstly, by using
this algorithm, points are extracted from the surface’s massive measuring points and the offset value
between measuring points and their projection on the theoretical positions is calculated. Secondly, the
local extremum is extracted at the peak and valley of waviness according to the variation trend of the
offset value. Then its corresponding wavelength is calculated. Finally, the waviness is calculated based
on its definition. Experiments show that this method is highly efficient, and generates accurate results.

Key words: waviness, point projection on surfaces, local extremum, aircraft surface