Geometric weight and the density heatmap
Summary
Every object in an IFC model is eventually drawn as triangles. A wall needs a dozen; a pump modelled from the manufacturer's CAD file, with every bolt and fin, can need a hundred thousand. Most of the time a few classes or a handful of objects carry most of the triangles, and they decide how fast the model opens, how much memory it needs and whether it can be viewed on a tablet on site.
Why weight matters
- Performance. Viewers, coordination tools and digital twins slow down or run out of memory long before the number of objects becomes a problem.
- Use on site and in operation. Facility managers and inspectors open models on laptops and tablets. A model that needs a workstation will not be used there.
- It is usually avoidable. The detail that makes a model heavy (screw threads, grilles, text engraved in 3D) rarely adds information anyone downstream needs.
How the check scores
The check uses the average number of triangles per object that has geometry:
| Triangles per object | Score | What it means |
|---|---|---|
| 150 or less | 100 | Light Efficient; runs smoothly in any viewer. |
| 150 to 600 | 100 down to 60 | Moderate Acceptable in standard viewers. |
| 600 to 2,000 | 60 down to 20 | Heavy Over-detailed objects make the model slow. |
| Over 2,000 | 10 | Very heavy Far more detail than viewers and downstream tools need. |
Between the thresholds the score falls in a straight line, so 375 triangles per object scores 80.
How triangles are counted
For the checks, the triangles are counted from the geometry definitions in the file, without building every mesh: an extruded profile gives a number of triangles that follows from its outline, a triangulated surface gives its own triangles, a circle counts as 32 segments, and so on. This is fast enough for very large files and gives the same answer every time. The Geometry that can be processed check therefore says estimate. The density heatmap and the 3D views are made from real meshes.
Openings and annotations are not counted as objects. An opening does add triangles to the wall it cuts, because the wall becomes more complex.
Related checks on the Geometry page
| Check | What it measures | Score |
|---|---|---|
| Heaviest 10 objects' share | The share of all triangles in the ten heaviest objects. | 100 at 10% or less, falling to 30 at 50%. Not scored for models under 200 objects. |
| Shape reuse (mapped geometry) | The share of placements that reuse one shape definition instead of storing a copy. | 50 plus 1.5 points per percent of reuse, up to 100. |
| Copy-pasted geometry | Identical shapes stored again and again without a shared type. | 100 minus 3 points per percent of copies. |
| Geometry interoperability | The share of objects built from geometry types that import safely elsewhere. | See The risks of complex IFC geometry types. |
The density heatmap
The heatmap is a top-down picture of the whole model, 2,048 by 2,048 pixels, in which every pixel shows how much fine geometry lies above or below it. Large, simple faces add little; many small triangles add a lot. Dark purple means coarse and simple, bright yellow means dense: the places where detail piles up.
- The brightness uses a logarithmic scale, so a single extremely dense object does not hide everything else.
- Openings, annotations and spaces are left out. The picture is framed on the bulk of the model, so one stray object far away does not shrink the rest to a dot.
- Click the picture to open it at full resolution.
Read it together with the weight figures beside it: the average says how heavy the model is, the heatmap says where.
The other geometry cards
- Where the geometry sits: total triangles per IFC class, the twelve heaviest classes. Usually one or two classes carry most of the weight.
- Detail vs. quantity: one bubble per class, placed by the number of objects and the triangles per object, sized by its total. Classes in the shaded area above 600 triangles per object are the over-detailed ones; a large bubble high and to the right is where simplifying pays off most.
- Heaviest objects: the ten objects with the most triangles, with their GlobalId and share of the model. Focus flies the 3D viewer to the object.
Making a model lighter
- Replace manufacturer detail with simple shapes. Equipment, fixtures and fittings downloaded from manufacturers are the usual cause. A box with the right size and connection points carries the same information.
- Use types and mapped geometry. One shape definition used 500 times is far lighter than 500 copies, and the shape reuse check rewards it.
- Check the export settings. Many tools export curved surfaces with a fineness setting; the highest setting is rarely needed.
- Start with the heaviest objects list. Fixing the top ten often removes a large part of the total.
Frequently asked questions
Is a heavy model a bad model?
Not necessarily. A fabrication model for steel or prefab elements may need the detail. The score says how easy the model is to use for everyone else; whether the weight is justified depends on what the model is for.
Why does the heaviest object have so many triangles?
Most often it is a product from a manufacturer's library, a curved object exported at a very fine setting, or something drawn as a mesh instead of a solid. The heaviest objects list gives its name and GlobalId so you can find it in the authoring tool.
My file has no heatmap. Why?
The heatmap needs geometry that can be turned into meshes. When it could not be made, the weight figures appear above the heaviest objects instead. A file without any geometry has no Geometry page.