Carbon Index — Solid Geometry & QTO (Bentley Parasolid B-Rep Engine)

The Solid Geometry & Quantity Take-Off (QTO) grid is the high-precision geometric analysis module of the Carbon Index application. Unlike conventional carbon calculators that rely on crude bounding box cuboids or unverified text fields, Carbon Index directly interfaces with Bentley's native Parasolid geometric kernel to extract true boundary representation (B-Rep) solid volumes, discounting internal voids, penetrations, and geometric chamfers.

Solid Geometry QTO Workspace

Solid Geometry & QTO Grid Interface

The Solid Geometry view provides engineer-grade transparency into how volumes, densities, and physical masses are derived:

  1. Geometry Resolution KPI Cards:
    • Solid Geometry Resolution: Number and percentage of elements resolved via true Parasolid solid extraction vs. bounding box fallbacks.
    • Total Net Volume & Mass: Aggregated net volume ($m^3$) and total structural mass ($\text{tonnes}$).
    • High Reconciliation Variance: Elements exhibiting
      gt;20%$ variance between solid B-Rep volume and bounding box cuboid (e.g. hollow sections, pipes, curved roofs).
  2. Real Estate & Filter Toolbar: Filter by geometry method (All, B-Rep Solids Only, BBox Fallbacks, High Variance (>20%), Excluded Scope).
  3. Class / Category Group Accordions: Hierarchical summary of elements, total volumes, average densities, and mass property triggers.
  4. Detailed Elements Table: Individual instance records displaying resolved geometry method, exact net volume, density, net mass, and variance percentage.

Parasolid B-Rep Volume Extraction Pipeline

Bentley Parasolid KernelIModelReadRpcInterfaceCarbonMassPropertiesServiceCarbon Index UIBentley Parasolid KernelIModelReadRpcInterfaceCarbonMassPropertiesServiceCarbon Index UITrigger "Read Mass Properties" (ClassName, ElementIds)Format CompressedId64Set payload (+CandidateIds)getMassPropertiesPerCandidate(candidates, operation=0)Query True B-Rep Closed Solid TopologyReturn Exact Volume (m3), Surface Area (m2), CentroidMassPropertiesResponse[]Compute Variance vs BBox & Update Asset Mass (V * density)Refresh QTO Grid & Recompute Summary KPIs

Technical Extraction Specifications:

B-Rep Solid Volume vs. Bounding Box Comparison

Bounding box estimation routinely overestimates material quantities by 30% to 300% on complex or hollow components. The table below demonstrates the accuracy improvements achieved via Carbon Index's Parasolid engine:

Element Type / ECClass Bounding Box Volume True Parasolid B-Rep Volume Variance Real-World Carbon Impact
Circular Hollow Section (CHS) Column $0.850\ m^3$ $0.125\ m^3$ $-85.3%$ Prevents $5.7\ \text{tCO}_2\text{e}$ over-reporting per column.
Precast Hollowcore Floor Slab $4.200\ m^3$ $2.680\ m^3$ $-36.2%$ Accounts for longitudinal void tubes accurately.
I-Beam Structural Section (UB 457) $0.410\ m^3$ $0.065\ m^3$ $-84.1%$ Prevents treating open web profiles as solid rectangular steel blocks.
Solid Concrete Footing / Pad $12.500\ m^3$ $12.500\ m^3$ $0.0%$ Confirms $100%$ accuracy on solid prismatic geometry.

Running Mass Properties on Demand

Users can initiate mass properties extraction at any time:

Read Mass Properties Trigger

  1. Open the Solid Geometry & QTO tab.
  2. Locate any EC Class card showing the BBox Fallback or Partial Solid chip.
  3. Click Read Mass Properties.
  4. The system sends the batch compressed candidate list to Bentley's iTwin RPC backend.
  5. Once returned, all elements update in real time with the exact B-Rep volume and recalculate embodied carbon instantly.
  6. The updated calculations are cached in local browser IndexedDB, with an alert banner inviting the user to Publish to iModel when ready.

Related Documentation