ABSTRACT
In our introductory section on affine geometry we studied geometric facts which depended on how lines and planes intersect. Thus we were interested in properties like parallelity, collinearity and the occurrence of certain division ratios. Now as the following picture showing a geometric figure and its shadow suggests, there are transformations arising in a very natural way which preserve these properties. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315136547/a57ae1f0-6f59-46bd-bbdd-35a521b486a1/content/page72_1.tif"/>
