As we will see below, semantic information is very important to enhance the blind persons capability to understand a 2D drawing. However if he or she can find out what is displayed, the geometric information alone could give much information about how it is constructed. It is also true for drawings made for children. Nevertheless at this point of time in a western culture, adult sighted people often prefer drawings which take into consideration the laws of optics. The perfect tool to produce such images is the camera.
Parallel lines seem to converge towards the more distant end.
Shadows indicate convex or concave parts and other properties. These pictorial cues for 3-D information from vision work on the assumption of an observer viewing from a single vantage point. There is no equivalent single vantage point for touch. Blind people perceive their environment using other sensory modalities to vision such as touch and hearing. The pictorial cues in vision do not apply in the same way for touch.