User's Guide

Virtualwind SketchUp Plugin Tools   →   Correcting Geometry   →   Correction Realities: A Warning

Correction Realities: A Warning

In the section on Creating Geometry, it was mentioned why watertight geometry is desireable in Virtualwind: watertight geometry can be exported to Virtualwind as Virtualwind Buildings (instead of Canopies), and Virtualwind simulates windflows around Buildings more accurately than it does around Canopies. When you are creating a geometry from scratch, you have full control from the outset on the dimensionality of the geometry: if you are conscientious, it is easy to consistently create three-dimensional geometry, and to catch departures as they appear. Except in pathological cases (like creating the Eiffel Tower, for example), creating an "All Building" model will require very little extra time compared to creating an arbitrary model with no regards to Buildings.

Correcting a model, however, is an entirely different scenario. Current models-creaters generally do not have Virtualwind's notion of watertight geometry in mind. There is nothing "wrong" with leaky surfaces and interior faces. If a billboard can be modelled satisfactorally in 2 seconds with a SketchUp Rectangle, why spend the extra time needlessly using SketchUp's Push/Pull tool to make it watertight?

Unfortunately, this presents a serious obstacle to someone wanting to correct already-created geometry. Some general-purpose model-creation techniques leave behind very difficult to correct non-watertight artifacts. These issues will be covered in the Common Problems section, but for now it is enough to recognize that many problems are not obvious how to correct – or even to recognize.

Model complexity is trending towards the increasingly complex. An informal survey of SketchUp Warehouse models in early 2008 suggested that typical models had roughly five to ten thousand edges; in early 2009, it is not uncommon to find models with fifty to a hundred thousand edges.

If you do indeed want to make a model fully watertight, be prepared to be patient. It is impossible to give exact numbers, but you should expect a typical thousand-edge Warehouse model to require about five hours to correct; a five-thousand edge model will require about 10 hours; a twenty-thousand edge model will probably take two days. These time estimates assume that you are an experienced SketchUp user, and an experienced "model correcter"; if you are new to SketchUp, even a thousand-edge model will probably take a full day.

None of this is meant to discourage you from trying. In fact, there is a certain spark of joy that can come from successfully correcting a Group, and correcting a whole model can be almost europhoric (especially after sinking twenty hours into it). If you like doing jigsaw puzzles, you will probably find that correcting models is similarly rewarding. If you hate jigsaw puzzles, you might want to take the shortcut discussed in the next section.