Drawings, models and BIM
A show drawing is not a picture of the show. It is a contract between departments about where things are, what they weigh and who is responsible — and the reason modern entertainment CAD is worth its learning curve is that it stops the drawing and the paperwork from ever disagreeing.
The distinction that explains everything
A line, and a thing that knows what it is
In general drafting, a light on a plan is a symbol: some lines on a layer. It looks right, it prints, and it knows nothing. If you move it, nothing else in the document notices. If you swap it for a heavier fixture, no total changes anywhere.
In entertainment CAD the same light is an object with data attached. It knows its type, weight, power draw, lens, colour, focus, channel, universe, address, the position it hangs on and the circuit it is on. Move it and the plot, the instrument schedule, the hookup, the load on that truss and the patch all update, because they are not separate documents — they are different views of one database.
That is the entire argument for the extra complexity, and it is also why exporting to a plain DWG at the end feels lossy. It is lossy. The geometry survives and the intelligence does not.
What actually gets produced
The drawing set a show runs on
Different venues and different countries name these differently, but the set is remarkably consistent — and almost all of it can come out of one model.
The tools
What each one is for, and what it is not for
The common language. Venues, architects and structural engineers will send you DWG, and expect DWG back. Precise, universal, and deliberately unopinionated: it draws what you tell it and attaches no meaning. Treat it as the exchange format and the survey base rather than as the place a show lives.
The industry default for lighting and scenic documentation, because of the object model above. Fixtures carry data, paperwork generates from the drawing, and the same file exports to previsualisation and to consoles. The learning curve is real and it buys you a set of documents that cannot silently disagree with each other.
Takes the rig you have drawn — trusses, hoists, bridles, the weight of every object hanging on it — and computes the loads. It tells you what each hoist is carrying, where a truss is over its limit, and what happens when you move a point. It is a calculation aid inside a competent process, not a substitute for a rigger or an engineer, and it is only ever as good as the weights and the structure you told it about.
Fast, forgiving, and excellent at answering "roughly, does this fit and what does it feel like" in an afternoon. Not a data model and not a documentation tool. Perfect for the conversation with a director; wrong as the source of truth for the build.
A complete free modelling, animation and rendering package. Strong for scenic visualisation, content, and anything that has to move. Weak as a drafting tool — dimensioned, annotated, printable drawings are not what it is for. Increasingly the bridge between design and a real-time engine.
Where complex scenic and structural geometry gets designed. Grasshopper makes the shape a set of rules rather than a set of surfaces, so changing a parameter regenerates everything downstream. The natural tool when a scenic element is a family of variations rather than one object.
The venue’s own world. A BIM model carries data on every element of the building — structure, services, capacities — so it can be queried and checked for clashes rather than eyeballed. IFC is the open exchange format that lets a model move between packages. For touring work you mostly consume BIM: the venue’s model tells you where the steel is, what it takes, and where the services run. For installed and new-build work you contribute to it, and the discipline of doing so is what stops a lighting position from being discovered to occupy the same space as a sprinkler main.
Loads
What Braceworks is actually doing, and what it is not
Every fixture, motor, cable and scenic piece has a weight, and every one of those weights ends up somewhere. The question a rigging plot has to answer is where, and the answer is not obvious: a truss on three hoists does not put a third of the load on each, and moving one fixture two metres changes every reaction along the span.
Structural analysis inside the CAD package does that arithmetic continuously as the drawing changes, and flags the point where something exceeds its rated capacity. That is genuinely valuable, because the alternative is a spreadsheet that was accurate at one moment last Tuesday.
What it does not do is take responsibility. The result depends entirely on the weights you entered, the structure you modelled, the capacities you specified and the assumptions the software makes about how the pieces connect. A competent rigger reviews the output; nobody signs a load-in on a screenshot.
Where does the weight actually go?
A truss on three hoists does not put a third of the load on each, and moving one fixture two metres changes every reaction along the span. Drag a fixture along the truss below and watch the three points argue about it.
Illustrative statics for two supports at a time, to show the shape of the problem. Real load calculation belongs in Braceworks or its equivalent, reviewed by a competent rigger.
- Weights get left out, not entered wrong. The cable, the safety, the clamp, the scroller, the haze machine somebody clipped on at the end. A structural total is only as complete as the model.
- A venue DWG is a starting point, not a survey. It may be from before the last refurbishment, drawn in a different unit, or accurate about the building and silent about the steel. Verify anything you are going to hang from.
- Agree the origin before anyone draws. Centre line and setting line, or the venue’s grid — but written down, once, and used by lighting, video, audio, automation and scenic alike. This is the same coordinate problem as on the systems page, and it is where tracked systems fail.
- Units bite silently. Millimetres against metres against feet and inches, a model imported at 1/1000 scale that still looks fine on screen. Check a known dimension immediately after any import.
Exchange
What survives a hand-off, and what quietly does not
Almost every problem in a drawing hand-off is a lost attribute rather than lost geometry. It is worth knowing what each format is for, because the shape usually arrives fine and the data does not.
| Format | Carries | What to watch |
|---|---|---|
| DWG / DXF | Geometry, layers, blocks, text. 2D and some 3D. | The universal exchange, and the one that drops object data. Agree layer naming and units in advance or expect an evening of cleanup. |
| IFC | A building model: elements with properties and relationships. | The open BIM format. Big files, and a round trip through another package rarely returns everything. |
| GDTF | A fixture: DMX footprint, modes, geometry, physical data. | The open format that lets one fixture definition serve the console, the previz tool and the CAD package. Check the file matches the firmware the fixture is actually running. |
| MVR | A whole rig: fixtures, positions, structures, in one scene. | Built on GDTF. This is what makes handing a plot to a console or a previz system a transfer rather than a re-entry. Support varies by version — test it before you rely on it. |
| FBX / glTF / OBJ | Meshes, materials, sometimes animation. | The route into a render engine. Scale and axis convention are the first two things to check, every time. |
| What the drawing looked like. | Perfect for issuing, useless for working. Never the only copy of anything. |
The point of it all
A drawing is a contract
It is tempting to treat drawings as documentation — something produced after the design, for the file. On a show they are the opposite: they are how departments agree with each other before anything is built, and how a disagreement is discovered on paper rather than at 40 feet.
That is why the boring parts are the important ones. A stated scale. A stated origin. A revision number and a date. A legend that says what the symbols mean. A title block that says who drew it and who to ask. None of that makes the drawing better looking, and all of it is what makes it usable by somebody who was not in the room.
The good news is that the tools above will do almost all of it for you, from one model, as long as the model is built with data in it rather than lines that look like data.
This page describes the shape that is common across them; the naming, the standard sheet set and the responsibility split differ by country and by venue. If your region does it meaningfully differently, open an issue — regional practice is exactly the sort of thing this site should record rather than flatten.
- Geometry or data?
- What does Braceworks actually do?
- What are GDTF and MVR?
Where to go next
These pages are a chain rather than a library — the next one along usually answers the question this one raised.
Everything on this page, in the index
Each of these has its own entry with sources, ports, gotchas and an open gap where a field is missing.