CONCLUSIONES Y RECOMENDACIONES
DECLARACIÓN COOPERATIVISTA DE LA CIUDAD DE LOJA
After proposing repair suggestions for a design that does not satisfy desired goals, TAC performs repairs by carrying out the suggestions. The result is a set of new designs. Carrying out sugges-tions is straightforward, but involves details having to do with the automatic derivation of territo-ries from design elements.
Creating a New Design
Carrying out a suggestion for a design is a four step process: Make a copy of the design, perform the proposed modification on the new design, update the circulation model, update the territory model.
A modification operator may affect all models that represent a design. It changes the design element model, for example, by removing, moving, or puncturing a particular design element.
Since the edges in an edge model are derived from the design elements, each of these operators also changes the edge model. The circulation model is changed since it is derived from the edge model. It must be updated by creating nodes and arcs for new doorways, and by removing arcs for doorways (and their corresponding nodes) that have been removed. The territory model may or may not be changed. If a design element’s edges help form a territory boundary and the design element is moved or removed, then the territory’s boundary may change. If as a result of changes, the territory is no longer well-formed, by which we mean bounded by a connected set of edges, then it is removed. TAC then attempts to redefine the territory using both old and new edges. An example of TAC’s territory redefinition procedure is shown later in this section.1
Identity Issues
Repair suggestions are intended, of course, to cause an unsatisfied goal to become satisfied.
After carrying out a suggestion, TAC checks the resulting new design to see if the unsatisfied goal is now satisfied. Given a goal specifying that the Living territory in the Tomek house be visually open from the Dining territory, for example, TAC suggests removing the fireplace, creates a new design with the fireplace removed, then checks whether the Living territory in the new design is
1. Many computational geometry routines depend on having closed polygons, hence our insistence on well-formedness.
TAC redefines territories and defines new territories by walking through all edges in the new edge model, identifying all closed polygons not already part of defined territories.
visually open from the Dining territory. In this example, checking for goal satisfaction is straight-forward because the two design objects in the goal—the Living and Dining territories—have not changed. Even though the fireplace helped bound the Living territory in the previous design, removing it does not change the territory’s bounds: the fireplace and stair shared an edge, so that edge, now belonging only to the stair, still bounds the territory. Figure 6.1 shows the unchanged territory boundaries and the results of TAC’s visual-openness calculations for the original design and the new design.
Figure 6.1: Tomek territory models: with fireplace and without.
Shaded region is visible; each * is a viewpoint. Visual-openness of Living from Dining in Tomek (top model) is 0.44; with fireplace removed, it is 1.0 (assuming the edge shared by fireplace and stair is replaced by a stair railing).
What happens if a new design is modified in such a way that one of the design objects speci-fied in the intended goal no longer exists? How can the goal be evaluated in the new design? This problem is a difficult and important one and has been encountered in other evaluation and repair systems in which objects can appear and disappear (e.g. Simmons, 1988). We did not study the problem extensively, but rather mimicked what human designers do in such situations: map objects in a new design to objects in a previous design using an “approximately the same” test. An
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Consider the Chatham house introduced earlier, and imagine that we want the Living territory to be visually open from the Dining territory. TAC finds that the Living territory is not visually open from the Dining territory. Results of the visual openness calculation are shown in Figure 6.2.
Figure 6.2: Territory model for Chatham house, first floor.
Region of Living territory visible from Dining is shown shaded;
visual-openness value is 0.55.
One of TAC’s suggestions for making the Living territory visually open from the Dining is to rotate the stair. Figure 6.3 shows a new territory model with the stair rotated and the region of the Living territory now visible from the Dining territory.
Figure 6.3: New Chatham design with stair rotated.
visual-openness value of Living from Dining is 0.94.
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While the Living territory in the new design is visually open from the Dining territory, the territory bounds have changed (Figure 6.4), and the original territories for which the goal was specified no longer exist. The original territories were removed because they were not well-formed after stair rotation. TAC was able to create new territories based on the new stair location and map them to the original territories.2 It then evaluated the goal with respect to the new territo-ries. In other cases, the physical form may be so changed that new territories cannot be mapped to old ones. In such a situation, it is not possible to check for goal satisfaction, and TAC signals this to the designer.
Figure 6.4: Bounds for Living and Dining territories.
Top shows user-defined territories in original design;
bottom shows TAC-defined territories in new design.
2. The territories were partially bounded by edges of the stair and edges projected from the stair. Rotation of the stair created new projected edges and changed edge locations in such a way that the original territories were no longer well-formed (i.e. closed polygons). TAC defined new territories by identifying all closed polygons in the new design. It then
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Bookkeeping Issues
To simplify keeping track of edges and their derivations, and to ensure that no edges overlap, projected edges derived from the design element to be modified are removed prior to the modifi-cation. (Recall that projected edges do not correspond to design elements, but rather are exten-sions of one or more edges derived from design elements. See Section 3.1 for examples.) The modification is then carried out, and new projected edges are added back for the modified design element. Some of these new projected edges may help form boundaries for new territories. In the above example, the projected edges for the stair were removed prior to rotation. Figure 6.5 below shows the overlapping edges that result if projected edges are not removed prior to rotating the stair. See Appendix F for more details about removing projected edges.
Figure 6.5: Rotating a stair without removing projected edges.
To simplify an edge model after a modification has been carried out, TAC attempts to decrease the number of edges by combining neighboring edges into single edges where possible.3 If edges are not combined, the edge models for designs that are several modifications from an original design run the risk of containing many small edges: with each new modification, new edges are added, each of which may split existing edges (since edges do not overlap). In a model with many small edges, tests for sameness among designs are less efficient and more difficult, and the number of suggestions needlessly increases when a modifier is dependent on particular edge loca-tions. Combining edges where possible helps guard against this situation.
3. Two edges can be combined if they have the same derivation information and their shared endpoint has only the two edges.
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