Object models for computer aided design

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57 :te 􁪽􋴚􁪽􋵲rs: level cf units 􁪽􋵮ntc which the Trodel is Eo:􁪽􋴚 􁪽􋵦ff􁪽􋵣c􁪽􋵥ency a􁪽􋵤d clarity are depende􁪽􋵴t 􁪽􋴿?on the s:ze a􁪽􋵤d s:r􁪽􋵣cture of the 􁪽􋴚􁪽􋴚􁪽􋵴ts i􁪽􋵴to wtich the rnc􁪽􋵥e: is 􁪽􋵡ar:􁪽􋴺::one􁪽􋴮. O􁪽􋵦fortunately, the protlerr of deterrr􁪽􋵮ninq the proper ?arti:􁪽􋵣c􁪽􋴚􁪽􋵮ng is not easilv resolved. ':he 􁪽􋵲roper chcices are uscally degendent both on the 􁪽􋵡ature of the reso􁪽􋵲rc􁪽􋴵5 a􁪽􋵡ailatle anc the n2:􁪽􋵲re of the 􁪽􋵯odel to be constructec. It is, in fact, in choosing s u ch pz r t i t i on i ne c f be::: data ano c r c c e du r e s :hat IT::.Jcn of the "art" of C"c.,. .... pt.;rpose is to 􁪽􋵯odel physical objects and interact graphically with these ffiodels. Ke would like, f􁪽􋵲r:her, t􁪽􋵴 te a􁪽􋵬le to use sITall co􁪽􋵰pt.;ters for tts purpose. In 􁪽􋵥ealir.9 􁪽􋵩i􁪽􋴚􁪽􋵰 physicsl environ􁪽􋵥ents there seerrs to be a environ􁪽􋵥ent into distinct physical objects. \\e ...:ill call tnr:i::onec "c c j e c t s " to s uc c e s t this concept. Objects 􁪽􋵩ill be defined as ielatively large data str􁪽􋵣ctures 􁪽􋵩ith a C 0 rr r: 1 e x (i. e. 1 i. n ked) i n t ern a 1 s t r c C t 11 r e • E Y a 11 cv i n 9 t rJ i 5 linked internal structure it is possible to collapse the cl􁪽􋵳ster5 discussed in chapter 2 (e.g. a polyhedron) into single objects.