The computer--aidedsolution to algorithmic problemsis becoming moreandmoreimportant in variousapplicationdomains.This is in particular true for computationalgeometry.For example,geometric problemsnaturally arisein imageprocessing,computergraphics, andall kinds of computer-aideddesign,just to mention a few. Even more,the generaltendencytowardsthe application of visual aidsin virtually all fields of science,technology,andbusinessraises manynew,unexpectedgeometricchallenges. A soundmathematicaltreatmentof theseproblemsanda systematiccomputational study on the resulting algorithms aredesirable. However, in practice, there are often obstaclesto such an attempt. In this paper, we will systematically discussour experienceswith a few obstaclesthat occurredin four of our projects andsignificantly influenced our reasoningon algorithmsin eachof them.