A DIMENSION references the block "that contains the entities that make up
the dimension picture", and that block is the picture: AutoCAD requires
it and draws it, BricsCAD draws it when present and only renders from the
dimension variables when it is missing. OCS re-derived the picture from
DIMVARS every time and ignored the block entirely.
That works while a style agrees with what the drawing actually drew. A
Revit-exported schedule here does not: its style stores DIMTXT already in
drawing units beside a DIMSCALE meant to scale it, so the text came out
three hundred times too tall, and each dimension carries a DIMFXL
override that is likewise already in drawing units, so the extension
lines ran nearly a million units past the points they measure.
Neither is guesswork about units now. The block holds the geometry the
drawing was authored with, so it is drawn: the contents are already in
world space and the block's base point is the origin, and the identity
instance that carries them exists only to reuse the scene graph's
ByBlock / layer-0 colour resolution. Every wire answers to the dimension,
so a pick still selects the dimension rather than one of its pieces.
Re-deriving stays as the fallback for a dimension with no block.
Annotative dimensions keep the old path: their several representations
are separate blocks and choosing between them is what the annotation
machinery already does, while the doctrine above assumes one picture.
A picture is only good while its inputs hold, so it is dropped when they
change: editing a dimension's properties, and saving the dimension style
it is drawn with. Entity edits already dropped it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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