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#### 4.4.1 Limits on `sketch` error detection

`Sketch` catches many kinds of errors, but not all. For example, options that sketch does not recognize, even incorrect ones, are quietly copied to `PSTricks` commands in the output. It is also unfortunately easy to produce `sketch` inputs that lead to no picture at all (improper vertex ordering causes everything to be culled), to pictures that are too big or too small for `PSTricks` to draw (due to limits of TeX math), and pictures that look nothing like what was intended. A picture with one of these problems can be difficult to “debug.” We offer the following suggestions.

- Follow the suggested incremental development method described in Overview.
- Always maintain one or two back-versions of a drawing so that it is easy to fall back to a known-good increment.
- When using `perspective`, ensure all finally transformed objects satisfy z<0 and, in fact, do not come very close to the origin at all.
- Temporarily use `cull=false` to see where vertex ordering problems lie.
- Use temporary changes of color of one or more objects to ensure that your understanding of the scene geometry is correct.
- If `PSTricks` complains about something, inspect the output directly for clues.