Humans estimate distance based on several different factors, such as shadows and relative positions. The most important method for estimating distance, triangulation, is performed unconsciously. Triangulation is based on the fact that light from distant objects strikes each eye at a slightly different angle. Your brain can then use that information to determine the angle w as shown in the figure. The figure shows an isosceles triangle LOR, with its basement LR parallel to the horizontal. Side OL makes an angle of theta subscript a with the vertical. The bisecting line of angle LOR is normal to the basement and has a length of D uppercase. The angle between it and OL is theta subscript w. The distances from the point of intersection between the bisecting line and the basement, and both L and R are l. In the figure, points L and R represent your left and right eyes, respectively. The distance between your eyes is 2l, and the distance to the object, point O, is D