easy-ifc.ts

import { IFC4, IfcAPI, IfcLineObject, Schemas } from 'web-ifc'

const ID_CHARS = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_$'

/**
 * This library creates an object and context to work with web-ifc
 * as web-ifc is provides simply types and a way to write to files
 */
export class EasyIfc {
    public ctx: IfcAPI
    public modelID: number
    public unit: IFC4.IfcUnitAssignment
    public wcs: IFC4.IfcAxis2Placement3D

    /**
     * Creates a new EasyIfc Object, used for creating IFC files.
     * Used internally by the EasyIfc class. Use EasyIfc.create() to create a new EasyIfc Object.
     * @param _ctx an IfcAPI object
     * @param name the name of the model
     */
    private constructor(_ctx: IfcAPI, name: string) {
        this.ctx = _ctx

        this.modelID = this.ctx.CreateModel({
            schema: Schemas.IFC4,
            name,
            authors: ['Patrick Stillhart'],
        })

        const metric = this.setupMetric()
        this.unit = metric[0]
        this.wcs = metric[1]
    }

    /**
     * Creates a new ifc object builder
     * @param name the name of the model
     * @returns a new EasyIfc Object
     */
    static async create(name: string) {
        const ctx = new IfcAPI()
        await ctx.Init()
        return new EasyIfc(ctx, name)
    }

    /**
     * Generates IFC compliant ids
     * specification: https://standards.buildingsmart.org/IFC/RELEASE/IFC2x3/TC1/HTML/ifcutilityresource/lexical/ifcgloballyuniqueid.htm
     * implemenation based on: https://github.com/IfcOpenShell/IfcOpenShell/blob/master/src/ifcopenshell-python/ifcopenshell/guid.py
     * @returns an IFCGloballyUniqueId
     */
    static guid() {
        const g = crypto.randomUUID().replace(/-/g, '')

        const bs: number[] = []
        for (let i = 0; i < g.length; i += 2) {
            bs.push(parseInt(g.slice(i, i + 2), 16))
        }

        const b64 = (v: number, l = 4) => (Array.from({ length: l })
            .map((_, i) => ID_CHARS[Math.floor(v / (64 ** i)) % 64])
            .reverse()
            .join("")
        )

        const newId = [
            b64(bs[0], 2),
            ...Array
                .from({ length: Math.floor((bs.length - 1) / 3) })
                .map((_, i) => b64((bs[i * 3 + 1] << 16) + (bs[i * 3 + 2] << 8) + bs[i * 3 + 3]))
        ].join("")

        return new IFC4.IfcGloballyUniqueId(newId)
    }

    /**
     * Sets the context up for the metric unit system
     * @returns a tuple of the unit assignment and the axis2placement3d
     */
    setupMetric(): [IFC4.IfcUnitAssignment, IFC4.IfcAxis2Placement3D] {
        const unit = this.add(new IFC4.IfcUnitAssignment([
            new IFC4.IfcSIUnit(IFC4.IfcUnitEnum.LENGTHUNIT, IFC4.IfcSIPrefix.MILLI, IFC4.IfcSIUnitName.METRE),
            new IFC4.IfcSIUnit(IFC4.IfcUnitEnum.AREAUNIT, null, IFC4.IfcSIUnitName.SQUARE_METRE),
            new IFC4.IfcSIUnit(IFC4.IfcUnitEnum.VOLUMEUNIT, null, IFC4.IfcSIUnitName.CUBIC_METRE)
        ]))

        const cartPoint = this.add(new IFC4.IfcCartesianPoint([
            new IFC4.IfcLengthMeasure(0),
            new IFC4.IfcLengthMeasure(0),
            new IFC4.IfcLengthMeasure(0),
        ]))

        const axis = this.add(new IFC4.IfcDirection([
            new IFC4.IfcLengthMeasure(0),
            new IFC4.IfcLengthMeasure(0),
        ]))

        const dir = this.add(new IFC4.IfcDirection([
            new IFC4.IfcLengthMeasure(1),
            new IFC4.IfcLengthMeasure(0),
        ]))

        const wcs = this.add(new IFC4.IfcAxis2Placement3D(
            cartPoint,
            axis,
            dir
        ))

        return [unit, wcs]
    }

    /**
     * Adds an object to the context
     * @param object the object to add
     * @returns the object
     */
    add<T extends IfcLineObject>(object: T) {
        this.ctx.WriteLine(this.modelID, object)
        return object
    }

    /**
     * Compiles the context
     * @returns the compiled context
     */
    compile() {
        return this.ctx.SaveModel(this.modelID)
    }

    /**
     * Adds a 3D context
     * @returns the 3D context
     */
    add3dContext() {
        return this.add(new IFC4.IfcGeometricRepresentationContext(
            new IFC4.IfcLabel('3D'),
            new IFC4.IfcLabel('Model'),
            new IFC4.IfcDimensionCount(3),
            new IFC4.IfcReal(1.E-05),
            this.wcs,
            null,
        ))
    }

}

scaffolding.ts

export function createWorldScaffolding(easyIfc: EasyIfc, visualContext: IFC4.IfcGeometricRepresentationContext) {
    const project = easyIfc.add(new IFC4.IfcProject(
        EasyIfc.guid(),
        null,
        new IFC4.IfcLabel('Kabelschacht'),
        null,
        null,
        null,
        null,
        [visualContext],
        easyIfc.unit
    ))

    // ifc structure
    const site = easyIfc.add(new IFC4.IfcSite(
        EasyIfc.guid(),
        null,
        new IFC4.IfcLabel('Baustelle'),
        new IFC4.IfcText(''),
        null,
        null,
        null,
        null,
        null,
        null,
        null,
        null,
        null,
        null
    ))
    easyIfc.add(new IFC4.IfcRelAggregates(
        EasyIfc.guid(),
        null,
        null,
        null,
        project,
        [site]
    ))

    // in most examples i've seen there is also a building and a building storey
    // however, it doesn't seem to be necessary for a kabelschacht

    /*
    const building = easyIfc.add(new IFC4.IfcBuilding(
        EasyIfc.guid(),
        null,
        new IFC4.IfcLabel('Gebaeude'),
        new IFC4.IfcText(''),
        null,
        null, null, null, null, null, null, null
    ))
    easyIfc.add(new IFC4.IfcRelAggregates(
        EasyIfc.guid(),
        null,
        null,
        null,
        site,
        [building]
    ))

    const buildingStorey = easyIfc.add(new IFC4.IfcBuildingStorey(
        EasyIfc.guid(),
        null,
        new IFC4.IfcLabel('Erdgeschoss'),
        new IFC4.IfcText('Datum'),
        null,
        null, null, null, null,
        new IFC4.IfcPositiveLengthMeasure(0)
    ))
    easyIfc.add(new IFC4.IfcRelAggregates(
        EasyIfc.guid(),
        null,
        null,
        null,
        building,
        [buildingStorey]
    ))
    */

    return {
        project,
        site,
        // building,
        // buildingStorey
    }
}