Object models for computer aided design

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9 . f 8 f -c􁪽􋴚 􁪽􋴚􁪽􋴚􁪽􋴚􁪽􋴴 4 odae􁪽􋵥 each with 􁪽􋵛 [,ave an average 0_ ' aces ec: I, .. ,;.",,1; "'" .• - s􁪽􋵆F?crt grapr.:c interaction. Engi􁪽􋵥eerin? offices are 􁪽􋵯oin􁪽􋵳s, the n􁪽􋴚􁪽􋴚􁪽􋵥er of pci􁪽􋵴t accesses is lOO x 1000 x 8 x 4 x 2 = 6,400,000. The i􁪽􋵰plication of access nu􁪽􋵢bers of this scale is clearly t􁪽􋵡at the 􁪽􋵯ode1ing eys:err must provide very high speed access tc detail information like points in order to 􁪽􋵡ake this ki􁪽􋵤d of a􁪽􋵡alysis practical. 1.4 Corrputer Graphics Both the ore body interpretation and the excavation design task require 3D graphic interaction. Since we have defined the problem domain such that we are dealing with physical objects whose size, shape, and position are vital attributes, it is necessary for the modeling system to fi:led with pictures on paper. One wants to replace the peper, not the Fictures. The role played by spatial information and graphic , interaction is an important property of a ITodeling systeffi. If the needs for generating and interacting with pictures are given too little att􁪽􋵮ntion, one is not likely to be able to provide the access speed necessary for effective 3D interaction. The ability to move pictures in real time is important even in the design of s􁪽􋵣ct static things as