How to initialize Autodesk Forge 3D viewer correctly from BIM BCF Topic Viewpoint?

I am trying to initialize the Autodesk Forge 3D viewer correctly based on BIM topic-visualization data from a BCF file.

I have uploaded the 3D model (IFC) to Autodesk API, it has been processed and i can visualize/navigate the model successfully using the Autodesk Forge 3D viewer.

I have used the same 3D model (IFC) in Nemetschek SOLIBRI to create a Topic and exported it using the BIM BCF 2.1 standard (see https://github.com/buildingSMART/BCF-XML).

XML-Data from VisualizationInfo:

<PerspectiveCamera>
  <CameraViewPoint>
      <X>2.803843040759871</X>
      <Y>14.568845808384443</Y>
      <Z>0.8249055320631105</Z>
  </CameraViewPoint>
  <CameraDirection>
      <X>0.4898262677194313</X>
      <Y>-0.8652456579090667</Y>
      <Z>0.1068652371988122</Z>
  </CameraDirection>
  <CameraUpVector>
      <X>-0.05264688190667085</X>
      <Y>0.09299722978166312</Y>
      <Z>0.9942735142195238</Z>
  </CameraUpVector>
  <FieldOfView>60.0</FieldOfView>
</PerspectiveCamera>

My attempt to set the same camera/view on Autodesk Forge 3D viewer:

viewer.restoreState(JSON.parse(`{
  "viewport": {
    "eye": [2.803843040759871, 14.568845808384443, 0.8249055320631105],
    "target": [0.4898262677194313, -0.8652456579090667, 0.1068652371988122],
    "up": [-0.05264688190667085, 0.09299722978166312, 0.9942735142195238],
    "projection": "perspective",
    "isOrthographic": false,
    "fieldOfView": 60.0
  }
}`));

Result: A Forge 3D viewer camera view which does NOT match the one seen in SOLIBRI nor the one saved as snapshot-png in the BCF file.

Maybe the IFC-model in SOLIBRI and the Autodesk-processed-IFC-model have different coordinate-systems or what could be the error?

Solution

The CameraDirection value is not the target parameter of the Forge viewer. You have to use the following formula to calculate it yourself.

{Target} = {CameraViewPoint} + {CameraDirection} * {CurrentFocalLength}

The full camera mapping of your issue view will be:

var lengthScale = 1000; //! Use viwer.model.getUnitString(), the model I loaded is in `mm`, and BCF camera definition is in `m`
// or var lengthScale = Autodesk.Viewing.Private.convertUnits('m', viewer.model.getUnitString(), 1, 1);
var eye = new THREE.Vector3( 2.803843040759871 * lengthScale, 14.568845808384443 * lengthScale, 0.8249055320631105 * lengthScale );
var sightVec = new THREE.Vector3( 0.4898262677194313, -0.8652456579090667,  0.1068652371988122 ).multiplyScalar( viewer.navigation.getFocalLength() );
var target = eye.clone().add( sightVec )
var up = new THREE.Vector3( -0.05264688190667085, 0.09299722978166312, 0.9942735142195238 );

//Since Forge Viewer will apply a global offset to the whole model
//var offsetMatrix = viewer.model.getData().placementWithOffset;
var offsetMatrix = viewer.model.getModelToViewerTransform();
var offsetEye = eye.applyMatrix4(offsetMatrix); 
var offsetTarget = target.applyMatrix4(offsetMatrix);
var fov = 60; //!<< from BCF

var cameraView = {
    aspect: viewer.getCamera().aspect,
    isPerspective: true,
    fov: fov,
    position: offsetEye,
    target: offsetTarget,
    up: up,
    orthoScale: 1
};

viwer.impl.setViewFromCamera( cameraView );

Appendix Converting viewer camera back to BCF viewpoint

let scale = Autodesk.Viewing.Private.convertUnits(viewer.model.getUnitString(), 'm', 1, 1);
let invOffsetMatrix = viewer.model.getInverseModelToViewerTransform();
let eye = viewer.navigation.getPosition().clone();
let sightDir = viewer.navigation.getEyeVector().clone().normalize();
let upVec = viewer.navigation.getCameraUpVector().clone();

let offsetEye = eye.applyMatrix4(invOffsetMatrix).multiplyScalar(scale);
let fov = viewer.navigation.getCamera().fov;

let bcfDoc = document.implementation.createDocument('', '', null);
let bcfDocPI = bcfDoc.createProcessingInstruction('xml', 'version="1.0" encoding="UTF-8"');
bcfDoc.insertBefore(bcfDocPI, bcfDoc.firstChild);

let visualizationInfoElem = bcfDoc.createElement('VisualizationInfo');
bcfDoc.appendChild(visualizationInfoElem);

let perspectiveCameraElem = bcfDoc.createElement('PerspectiveCamera');
visualizationInfoElem.appendChild(perspectiveCameraElem);

let cameraViewPointElem = bcfDoc.createElement('CameraViewPoint');
perspectiveCameraElem.appendChild(cameraViewPointElem);

let cameraViewPointXElem = bcfDoc.createElement('X');
cameraViewPointXElem.textContent = offsetEye.x.toFixed(14);
cameraViewPointElem.appendChild(cameraViewPointXElem);

let cameraViewPointYElem = bcfDoc.createElement('Y');
cameraViewPointYElem.textContent = offsetEye.y.toFixed(14);
cameraViewPointElem.appendChild(cameraViewPointYElem);

let cameraViewPointZElem = bcfDoc.createElement('Z');
cameraViewPointZElem.textContent = offsetEye.z.toFixed(14);
cameraViewPointElem.appendChild(cameraViewPointZElem);

let cameraDirectionElem = bcfDoc.createElement('CameraDirection');
perspectiveCameraElem.appendChild(cameraDirectionElem);

let cameraDirectionXElem = bcfDoc.createElement('X');
cameraDirectionXElem.textContent = sightDir.x.toFixed(14);
cameraDirectionElem.appendChild(cameraDirectionXElem);

let cameraDirectionYElem = bcfDoc.createElement('Y');
cameraDirectionYElem.textContent = sightDir.y.toFixed(14);
cameraDirectionElem.appendChild(cameraDirectionYElem);

let cameraDirectionZElem = bcfDoc.createElement('Z');
cameraDirectionZElem.textContent = sightDir.z.toFixed(14);
cameraDirectionElem.appendChild(cameraDirectionZElem);

let cameraUpVectorElem = bcfDoc.createElement('CameraUpVector');
perspectiveCameraElem.appendChild(cameraUpVectorElem);

let cameraUpVectorXElem = bcfDoc.createElement('X');
cameraUpVectorXElem.textContent = upVec.x.toFixed(14);
cameraUpVectorElem.appendChild(cameraUpVectorXElem);

let cameraUpVectorYElem = bcfDoc.createElement('Y');
cameraUpVectorYElem.textContent = upVec.y.toFixed(14);
cameraUpVectorElem.appendChild(cameraUpVectorYElem);

let cameraUpVectorZElem = bcfDoc.createElement('Z');
cameraUpVectorZElem.textContent = upVec.z.toFixed(14);
cameraUpVectorElem.appendChild(cameraUpVectorZElem);

let fieldOfViewElem = bcfDoc.createElement('FieldOfView');
perspectiveCameraElem.appendChild(fieldOfViewElem);
fieldOfViewElem.textContent = fov.toFixed(14);

let bcfVpConents = new XMLSerializer().serializeToString(bcfDoc);

Enjoy it!