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有很多与BIM以及被视作BIM设计应用程序的电脑辅助设计系统相关的问题。本节将对那些最常见的问题进行解答。
基于构件的参数化建模之优点和局限
参数化建模的一个主要优点是构件的智能化设计行为。自动化的低级别编辑功能内置在程序中，几乎就像设计人员的设计助理。然而，这种智能化需要付出代价。每种系统构件都有其自我行为和关联。结果就是，BIM设计应用程序本身就很复杂。每种类型的建筑系统都是由以各种不同方式创建和编辑的构件组成的，尽管是在类似的用户界面类型中将它们完成的。通常要花费数月才能精通BIM设计应用程序，进而高效地使用它。
一些用户喜欢的建模软件，特别是早期概念设计阶段使用的SketchUp, Rhino, and FormZ’s Bonzai并不是基于参数化建模的工具。然而，它们都有一套固定的几何编辑方式，这种编辑方式仅仅根据使用的曲面类型而变化。这种功能适用于所有构件类型，故而这些软件用起来更容易。因此，当把应用于墙的某个编辑操作应用于楼板时，也会产生同样的行为。在这些系统中，如果把用于定义构件类型及其功能意图的属性应用于所有构件类型，那么可以在用户选择而不是用户创建的时候添加这些属性。
所有这些系统允许曲面成组，为这些组命名并可为其添加属性。仔细地完成这些并结合一个匹配的界面，就可以将构件导出并用于其它方面，例如太阳能热吸收研究。这一点类似于人们使用AutoCAD 3D中的技巧。但是人们不会用这种建模方式用于完善设计，因为其构件没有与其它构件链接，而且还必须对构件进行单独空间管理。然而，对于初步设计来说，BIM技术与其特定构件的行为并不总能得到保证。这一点会在第五章详细探讨。
为什么不同的参数化建模软件不能相互转化模型？
人们常常问到为什么公司不能把模型在Revit与Bentley_建筑之间直接转换，或在ArchiCAD与Digital Project之间转换。从之前讨论的内容来看，原因很明显，这种互操作性的缺失正是由于不同的BIM设计应用程序依赖于它们基本构件和行为的不同定义。Bentley中的墙与Vectorworks或Tekla中的墙的行为方式不同。这些都是功能（涉及BIM工具中的规则类型和用于特定构件族定义的规则）不同的结果。这个问题只存在于参数化构件中，使用固定几何图元的构件则没有这个问题。如果构件形状能作为固定几何图元存在并且行为化的规则失效了，那么ArchiCAD中的构件就能在Digital Project中使用；Bentley中的构件也能在Revit中使用。这种转换方面的问题是可以解决的。问题在于转换构件行为（这通常不需要）。如果软件公司就一般建筑构件定义标准（不仅包括几何图元也包括构件行为）达成一致，构件行为也是可以转换的。在此之前，某些构件的转换就会受限或彻底失败。因了解决这些问题的需求使得实施这些方法是值得的，并且已经因此解决了多个问题，这种改进会越来越多。制造业同样存在这样的问题，但尚未解决。
在施工、加工和建筑BIM设计应用程序中是否存在固有差异？
同一款BIM平台能否同时支持设计和加工深化设计？由于用于所有这些系统的基础技术有太多共同点，所以建筑设计和加工BIM设计应用程序之间不能相互供应产品并不是技术上的原因。Revit Structures和Bentley Structures在某种程度上也发生了这种情况。他们都在开发加工级别的BIM设计应用程序中的某些功能。
另一方面，有一些使用Tekla设计并建造房屋的案例。双方都致力于工程市场，并在较小程度上解决承包商市场方面的问题；但是，用于支持在这些信息丰富领域实现全生产应用的专业知识，取决于必要构件行为的主要前端嵌入，而这对于不同建筑系统及其生命周期需求来说是有明显差异的。在编制构件行为时，特定建筑系统构件行为的专业知识更容易被嵌入，例如结构系统设计。软件界面、报告以及其它系统方面的问题可能还会变化，但是处于中间地带的软件之间的小冲突可能会持续存在较长一段时间，毕竟每种软件产品都想要开拓其市场范围。
以制造为导向的参数化建模工具与BIM设计应用程序之间有很大不同吗？
能把用于机械设计的参数化建模系统用于BIM吗？在第2.1.3节（回复“B26”查看）和2.3.1节（回复“B32”查看）中提到了系统架构方面的差异。AEC市场已经采用了机械领域的参数化建模工具。基于CATIA的Digital Project就是很明显的例子。同样，Structure- works也是以Solidworks为平台的预制混凝土深化设计和加工的应用程序。这些适应性构建了目标系统域所需的对象和行为。建筑建模工具是自上而下的设计系统，而制造领域的参数化工具最开始是自下而上的模式。由于制造系统结构中，不同部件本质上是不同的“项目”，他们已经解决了在文件之间传递变更的挑战，这通常会使其更具扩展性。在其它方面，例如给排水、幕墙加工和管道工程设计中，我们可以期待看到机械领域的参数化建模工具和建筑业以及可加工级别的BIM设计应用程序在这些市场中群雄逐鹿。每个市场提出的功能范围仍在梳理中。市场即是战场。
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There are many questions associated with BIM and the computer-aided design systems that are considered BIM design applications. This p attempts to answer the most common ones.
Strengths and Limitations of Object-Based Parametric Modeling
One major benefit of parametric modeling is the intelligent design behavior of objects. Automatic low-level editing is built in, almost like one’s own design assistant. This intelligence, however, comes at a cost. Each type of system ob- ject has its own behavior and associations. As a result, BIM design applications are inherently complex. Each type of building system is composed of objects that are created and edited differently, though with a similar user interface style. Effective use of a BIM design application usually requires months to gain proficiency.
Modeling software that some users prefer, especially for early concept design, such as SketchUp, Rhino, and FormZ’s Bonzai, are not parametric modeling–based tools. Rather, they have a fixed way of geometrically editing objects, which varies only according to the surface types used. This functionality is applied to all object types, making them much simpler to use. Thus, an editing operation applied to walls will have the same behavior when it is applied to slabs. In these systems, attributes defining the object type and its functional intention, if applied at all, can be added when the user chooses, not when it is created. All of these systems allow the grouping of surfaces, giving the group a name and maybe assigning attributes. Done carefully and with a matching interface, the object can be exported and used in other areas, say solar gain studies. This is similar to the kinds of tricks people used to do with 3D AutoCAD. But one is not going to take this kind of modeling into design development because one object is not linked to other objects and must be spatially managed inpidually. An argument can be made that for preliminary design use, however, BIM technology with its object-specific behavior is not always warranted. This topic is explored further in Chapter 5.
Why Can’t Different Parametric Modelers Exchange Their Models?
It is often asked why firms cannot directly exchange a model from Revit with Bentley Architecture, or exchange ArchiCAD with Digital Project. From the overview discussed previously, it should be apparent that the reason for this lack of interoperability is due to the fact that different BIM design applications rely on different definitions of their base objects and their behaviors. A Bentley wall behaves differently than a Vectorworks wall or a Tekla wall. These are the result of different capabilities involving rule types in the BIM tool and also the rules applied in the definition of specific object families. This problem applies only to parametric objects, not those with fixed geometry. If the shapes are accepted in their current form as fixed and their behavioral rules are dropped, an ArchiCAD object can be used in Digital Project; a Bentley object can be used in Revit. The issues of exchange are resolvable. The problem is exchanging object behavior (which is not often needed). Behavior also could be exchanged if and when organizations agree on a standard for common building object definitions that includes not only geometry but also behavior. Until then, exchanges for some objects will be limited or will fail completely. Improvements will come about incrementally, as the demand to resolve these issues makes implementation worthwhile, and the multiple issues are sorted out. The same issue exists in manufacturing and has not yet been resolved.
Are There Inherent Differences in Construction, Fabrication, and Architectural BIM design applications?
Could the same BIM platform support both design and fabrication detailing? Because the base technology for all of these systems has much in common, there is no technological reason why building design and fabrication BIM design applications cannot offer products in each other’s area. This is happening to some degree with Revit Structures and Bentley Structures. They are developing some of the capabilities offered by fabrication-level BIM design applications.
On the other side, there are a few cases where Tekla has been used to design and build houses. Both sides address the engineering market and, to a lesser degree, the contractor market; but the expertise needed to support full produc- tion use in these information-rich areas will depend on major front-end embedding of requisite object behaviors, which are distinctly different for different building systems and their lifecycle needs. Expert knowledge of specific building system object behaviors is more readily embedded when it is codified, as it is, for example, in structural system design. The interfaces, reports, and other system issues may vary, but we are likely to see skirmishes in the middle- ground for a significant period of time, as each product attempts to broaden its market domains.
Are There Significant Differences Between Manufactuing-Oriented Parametric Modeling Tools and BIM Design Applications?
Could a parametric modeling system for mechanical design be adapted for BIM? Some differences in system architecture are noted in Sections 2.1.3 and 2.3.1. Mechanical parametric modeling tools have already been adapted for the AEC market. Digital Project, based on CATIA, is an obvious example. Also, Structure- works is a precast concrete detailing and fabrication product using Solidworks as a platform. These adaptations build in the objects and behavior needed for the target system domain. Building modelers are organized as top-down design sys- tems, while manufacturing parametric tools were originally organized bottom-up. Because of manufacturing systems’ structure, where different parts were originally different “projects,” they have addressed the challenge of propagating changes across files, making them often more scalable. In other areas, such as plumbing, curtain wall fabrication, and ductwork design, we can expect to see both mechanical parametric modeling tools and architectural and fabrication-level BIM design applications vying for these markets. The range of functionality offered in each market is still being sorted out. The market is the battleground.
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上一篇：第三十九期《BIM 手册》第二章_2.3.5节——构件管理和链接
