diff --git a/web-ifc-three/src/IFC/BaseDefinitions.ts b/web-ifc-three/src/IFC/BaseDefinitions.ts
index 69928d1..d28f057 100644
--- a/web-ifc-three/src/IFC/BaseDefinitions.ts
+++ b/web-ifc-three/src/IFC/BaseDefinitions.ts
@@ -222,4 +222,10 @@ export interface WebIfcAPI {
     GetFlatMesh(modelID: number, expressID: number): FlatMesh | Promise<FlatMesh>;
 
     SetWasmPath(path: string): void | Promise<void>;
+
+    /**
+     * Creates a map between element ExpressIDs and GlobalIDs.
+     * Each element has two entries, (ExpressID -> GlobalID) and (GlobalID -> ExpressID).
+     */
+    CreateIfcGuidToExpressIdMapping(modelID: number): void | Promise<void>;
 }
diff --git a/web-ifc-three/src/IFC/web-workers/BaseDefinitions.ts b/web-ifc-three/src/IFC/web-workers/BaseDefinitions.ts
index 5392390..2e6afd1 100644
--- a/web-ifc-three/src/IFC/web-workers/BaseDefinitions.ts
+++ b/web-ifc-three/src/IFC/web-workers/BaseDefinitions.ts
@@ -47,6 +47,7 @@ export enum WorkerActions {
     GetNameFromTypeCode = 'GetNameFromTypeCode',
     GetIfcEntityList = 'GetIfcEntityList',
     GetTypeCodeFromName ='GetTypeCodeFromName',
+    CreateIfcGuidToExpressIdMapping = 'CreateIfcGuidToExpressIdMapping',
 
     // Parser
     parse = 'parse',
@@ -146,6 +147,7 @@ export interface WebIfcWorkerAPI extends BaseWorkerAPI {
     [WorkerActions.GetNameFromTypeCode]: IfcWorkerEventHandler;
     [WorkerActions.GetIfcEntityList]: IfcWorkerEventHandler;
     [WorkerActions.GetTypeCodeFromName]: IfcWorkerEventHandler;
+    [WorkerActions.CreateIfcGuidToExpressIdMapping]: IfcWorkerEventHandler;
 }
 
 export interface SerializedVector {
@@ -171,4 +173,4 @@ export const ErrorRootStateNotAvailable = 'The root worker does not have any sta
 export const ErrorPropertiesNotAvailable = 'Error: Properties not available from web worker';
 export const ErrorParserNotAvailable = 'Error: Parser not available from web worker';
 export const ErrorBadJsonPath = 'Error: Model not available from web worker';
-export const ErrorBadJson = 'Error: The given Json could not be read as a JS object';
\ No newline at end of file
+export const ErrorBadJson = 'Error: The given Json could not be read as a JS object';
diff --git a/web-ifc-three/src/IFC/web-workers/handlers/WebIfcHandler.ts b/web-ifc-three/src/IFC/web-workers/handlers/WebIfcHandler.ts
index 41fe081..1032344 100644
--- a/web-ifc-three/src/IFC/web-workers/handlers/WebIfcHandler.ts
+++ b/web-ifc-three/src/IFC/web-workers/handlers/WebIfcHandler.ts
@@ -71,6 +71,10 @@ export class WebIfcHandler implements WebIfcAPI {
          return this.handler.request(this.API, WorkerActions.GetTypeCodeFromName, { typeName });
     }
 
+    async CreateIfcGuidToExpressIdMapping(modelID: number): Promise<void> {
+        return this.handler.request(this.API, WorkerActions.CreateIfcGuidToExpressIdMapping, { modelID });
+    }
+
     async WriteLine(modelID: number, lineObject: any): Promise<void> {
         return this.handler.request(this.API, WorkerActions.WriteLine, { modelID, lineObject });
     }
@@ -165,4 +169,4 @@ export class WebIfcHandler implements WebIfcAPI {
     async SetWasmPath(path: string): Promise<void> {
         return this.handler.request(this.API, WorkerActions.SetWasmPath, { path });
     }
-}
\ No newline at end of file
+}
diff --git a/web-ifc-three/src/IFC/web-workers/workers/WebIfcWorker.ts b/web-ifc-three/src/IFC/web-workers/workers/WebIfcWorker.ts
index a4362dc..cf7931b 100644
--- a/web-ifc-three/src/IFC/web-workers/workers/WebIfcWorker.ts
+++ b/web-ifc-three/src/IFC/web-workers/workers/WebIfcWorker.ts
@@ -191,8 +191,13 @@ export class WebIfcWorker implements WebIfcWorkerAPI {
         this.worker.post(data);
     }
 
+    CreateIfcGuidToExpressIdMapping(data: IfcEventData) {
+        this.webIFC.CreateIfcGuidToExpressIdMapping(data.args.modelID);
+        this.worker.post(data);
+    }
+
     private nullifyWebIfc() {
         // @ts-ignore
         this.webIFC = null;
     }
-}
\ No newline at end of file
+}