Thatopen Syntax Properties

ThatOpen Property Queries and Classification

Overview

ThatOpen provides two complementary systems for organizing and extracting data from loaded BIM models:

1. Classifier — Groups fragment items by IFC category, building storey, model, or custom criteria. Produces ModelIdMap results for downstream operations (hiding, highlighting, data extraction).
2. FragmentsManager.getData() — Extracts IFC property data (property sets, quantity sets, type information, relationships) for targeted items.
3. ItemsFinder — Searches items across models using query parameters with category, attribute, and relationship filters.

All three operate on the fragment layer, not raw web-ifc. For direct web-ifc property access (GetLine, GetPropertySets), see thatopen-core-web-ifc.

Pipeline:

Loaded FragmentsModel
  ├─ Classifier.byCategory()      → classification groups
  ├─ Classifier.byIfcBuildingStorey() → storey groups
  ├─ Classifier.find({...})        → ModelIdMap (intersection)
  ├─ ItemsFinder.getItems(queries) → ModelIdMap (filtered)
  └─ FragmentsManager.getData(items) → IFC property data

Critical Warnings

1. ALWAYS classify models AFTER loading. Classification methods read data from loaded FragmentsModels. Calling byCategory() before any model is loaded produces empty groups.

2. ALWAYS call FragmentsManager.init(workerURL) before getData(). Property extraction runs in the web worker. Without initialization, getData() fails silently or throws.

3. NEVER assume classification groups persist across model loads. When a model is disposed and reloaded, ALWAYS re-run classification methods to rebuild groups.

4. ALWAYS use find() to get a ModelIdMap from classifications. NEVER manually iterate classifier.list to build item maps — find() handles intersection logic correctly across multiple classifications.

5. NEVER query properties for thousands of items at once without pagination. getData() runs in the worker but still serializes results back to the main thread. Large result sets cause jank.

Classifier

Purpose

The Classifier organizes fragment items into named classification groups. Each classification (e.g., "Categories", "Storeys", "Models") contains named groups (e.g., "IFCWALL", "Ground Floor", "Arch Model") that map to sets of element IDs via ModelIdMap.

Data Structure

classifier.list: DataMap<string, DataMap<string, ClassificationGroupData>>
//                │                  │                │
//                classification     group name       group data (items + query)
//                name

ClassificationGroupData contains:

• A get() method returning Promise<ModelIdMap> — the items in the group
• Optional query configuration for dynamic groups
• Item storage maps keyed by model ID

Getting the Classifier

import * as OBC from "@thatopen/components";

const classifier = components.get(OBC.Classifier);

Built-in Classification Methods

byCategory(config?): Promise<void>

Groups all items by their IFC entity type (e.g., IFCWALL, IFCSLAB, IFCDOOR). Default classification name: "Categories".

await classifier.byCategory();
// classifier.list now has "Categories" with groups like "IFCWALL", "IFCSLAB"

byIfcBuildingStorey(config?): Promise<void>

Groups items by the building storey they belong to, using the ContainsElements IFC relationship. Default classification name: "Storeys".

await classifier.byIfcBuildingStorey();
// classifier.list now has "Storeys" with groups like "Ground Floor", "Level 1"

byModel(config?): Promise<void>

Groups items by their parent FragmentsModel. Default classification name: "Models".

await classifier.byModel();
// classifier.list now has "Models" with groups per loaded model

AddClassificationConfig

All three methods accept an optional config:

interface AddClassificationConfig {
  classificationName?: string;  // Override default name
  modelIds?: RegExp[];          // Filter: only classify matching models
}

Example with custom name and model filter:

await classifier.byCategory({
  classificationName: "Element Types",
  modelIds: [/arch/i]  // Only classify models whose ID matches "arch"
});

Querying Classifications with find()

find() accepts an object where keys are classification names and values are arrays of group names. It returns the intersection of all specified groups as a ModelIdMap.

// Type: ClassifierIntersectionInput
// Keys = classification names, Values = arrays of group names
const items = await classifier.find({
  Categories: ["IFCWALL"],
  Storeys: ["Ground Floor"]
});
// Returns: ModelIdMap of walls on the ground floor only

Intersection logic: When multiple classifications are specified, find() returns only items that appear in ALL specified groups. This enables powerful cross-classification queries.

Custom Groups

getGroupData(classification, group): ClassificationGroupData

Retrieves or creates a group. Use this to build custom classifications.

const groupData = classifier.getGroupData("Fire Rating", "REI 120");

addGroupItems(classification, group, items): void

Adds items to a specific group within a classification.

const wallItems: ModelIdMap = {
  [model.modelId]: new Set([42, 43, 44])
};
classifier.addGroupItems("Custom", "Selected Walls", wallItems);

removeItems(modelIdMap, config?): void

Removes items from the classifier. Without config, removes from ALL classifications.

// Remove specific items from all classifications
classifier.removeItems(itemsToRemove);

// Remove with config (RemoveClassifierItemsConfig)
classifier.removeItems(itemsToRemove, { /* config */ });

setGroupQuery(classification, group, query): void

Assigns a dynamic query to a group. When get() is called on the group, the query runs via ItemsFinder to produce fresh results.

classifier.setGroupQuery("Custom", "First Floor Walls", {
  name: "First Floor Walls"  // References a named ItemsFinder query
});

Aggregation Methods

aggregateItems(classification, query, config?): Promise

Groups items per classification using a query. Each item matching the query is placed into a group based on the aggregation callback.

aggregateItemRelations(classification, query, relation, config?): Promise

Groups items by IFC relationships. Used internally by byIfcBuildingStorey() to group elements by their containing storey via the ContainsElements relation.

await classifier.aggregateItemRelations(
  "Storeys",
  { categories: [/BUILDINGSTOREY/] },
  "ContainsElements"
);

FragmentsManager.getData()

Purpose

Extracts IFC property data for targeted items. Runs in the web worker for performance. Returns structured property information including property sets, quantity sets, type data, and relationship data.

Signature

getData(
  items: ModelIdMap,
  config?: Partial<ItemsDataConfig>
): Promise<Record<string, ItemData[]>>

Parameters

• items — ModelIdMap specifying which elements to query
• config — Optional Partial<ItemsDataConfig> controlling what data to retrieve

Return Value

Returns Record<string, ItemData[]>:

• Keys are model UUID strings
• Values are arrays of ItemData objects, one per queried element

ItemData

Each ItemData object represents the IFC data for one element. It contains the element's properties organized by their IFC structure: property sets, type information, attributes, and relationships.

Basic Usage

const fragments = components.get(OBC.FragmentsManager);

// Target specific elements
const items: ModelIdMap = {
  [model.modelId]: new Set([42, 43])
};

// Extract all available property data
const data = await fragments.getData(items);

for (const [modelId, itemDataArray] of Object.entries(data)) {
  for (const itemData of itemDataArray) {
    console.log("Element data:", itemData);
  }
}

Combined with Classifier

The most common pattern: classify first, then extract properties for the classified items.

const classifier = components.get(OBC.Classifier);
const fragments = components.get(OBC.FragmentsManager);

// Classify
await classifier.byCategory();
await classifier.byIfcBuildingStorey();

// Find walls on the ground floor
const wallItems = await classifier.find({
  Categories: ["IFCWALL"],
  Storeys: ["Ground Floor"]
});

// Extract properties for those walls
const wallData = await fragments.getData(wallItems);

ItemsFinder

Purpose

ItemsFinder searches and filters items across loaded models using structured query parameters. It supports filtering by IFC category, element attributes, and IFC relationships. Queries can be saved, named, and reused.

Getting ItemsFinder

const finder = components.get(OBC.ItemsFinder);

Creating Named Queries

const query = finder.create("First Floor Walls", [
  {
    categories: [/WALL/],
    relation: {
      name: "ContainedInStructure",
      query: {
        categories: [/STOREY/],
        attributes: {
          queries: [{ name: /Name/, value: /01/ }]
        }
      }
    }
  }
]);

Query Parameters (ItemsQueryParams)

interface ItemsQueryParams {
  categories?: RegExp[];      // Filter by IFC category (regex match)
  relation?: {                // Filter by IFC relationship
    name: string;             // Relationship name (e.g., "ContainedInStructure")
    query: ItemsQueryParams;  // Nested query for related items
  };
  attributes?: {              // Filter by element attributes
    queries: Array<{
      name: RegExp;           // Attribute name pattern
      value: RegExp;          // Attribute value pattern
    }>;
  };
}

Executing Queries

// Execute with getItems()
const items = await finder.getItems(
  [{ categories: [/WALL/, /SLAB/] }],
  {
    modelIds: [/arch/i],             // Optional: filter models by ID pattern
    aggregation: "union"             // "union" or "intersection"
  }
);
// Returns: ModelIdMap

Auto-Generate Category Queries

// Create queries for all geometric categories in loaded models
const categoryNames = await finder.addFromCategories();
// Returns: string[] of category names found (e.g., ["IFCWALL", "IFCSLAB"])

Serialization

// Export queries for storage
const serialized = finder.export();

// Import previously saved queries
await finder.import(serialized);

IFC Relationships in Fragment Context

The fragment system preserves key IFC relationships that can be queried through Classifier and ItemsFinder:

Spatial Structure via Classification

The spatial hierarchy (Project > Site > Building > Storey > Space) is accessible through the Classifier's storey classification:

await classifier.byIfcBuildingStorey();

// Access storey groups
const storeyGroups = classifier.list.get("Storeys");
if (storeyGroups) {
  for (const [storeyName, groupData] of storeyGroups) {
    const items = await groupData.get();
    console.log(`${storeyName}: ${Object.keys(items).length} models`);
  }
}

Property Sets and Quantity Sets

IFC models contain two types of element metadata accessible via getData():

1. Property Sets (Pset_) — Named groups of properties assigned via IfcRelDefinesByProperties. Common examples: Pset_WallCommon, Pset_DoorCommon. Contains IfcPropertySingleValue entries with name-value pairs.

2. Quantity Sets (Qto_) — Physical measurements assigned via the same relationship. Common examples: Qto_WallBaseQuantities, Qto_SpaceBaseQuantities. Contains typed quantities (length, area, volume, weight, count).

For detailed IFC property set and quantity set schemas, see the ifc-bim-standards skill.

Workflow: Classify, Query, Extract

The standard workflow for working with IFC properties in ThatOpen:

1. Load model          → FragmentsModel in scene
2. Classify            → Classifier.byCategory(), byIfcBuildingStorey()
3. Query               → Classifier.find() or ItemsFinder.getItems()
4. Extract properties  → FragmentsManager.getData(items)
5. Use the data        → Display in UI, export, validate

ALWAYS follow this order. Classifying before loading produces empty groups. Extracting properties without targeting specific items wastes worker bandwidth.

Quick Reference

Related Skills

• thatopen-core-fragments — FragmentsManager, ModelIdMap, worker setup
• thatopen-core-web-ifc — Raw web-ifc property access (GetLine, GetPropertySets)
• thatopen-core-architecture — Component system, world setup
• thatopen-syntax-ifc-loading — IfcLoader configuration, WASM setup
• thatopen-impl-viewer — Full viewer setup including classification UI

References

• references/methods.md — Classifier API, getData config, ItemsFinder
• references/examples.md — Classify, find, getData, spatial queries
• references/anti-patterns.md — Wrong query patterns, missing classification