A method and system for scanning comprises rotating a scanning chassis of an optical scanner to create an acute angle between the scan line and a scanning direction, such that the scanning chassis has two ends, and moving the scanning chassis in the scanning direction and with the acute angle between the scan line and the scanning direction, both two ends of the scanning chassis being moved in the scanning direction, while one of the two ends is moved more slowly than the other one so that the scanning chassis is made to be rotated with the acute angle.