@Override
  public void configure() throws Exception {
    // We will now read this from the Configuration. The detector needs to be preconfigured!
    // detector = (XRayDetector) UserUtil.queryObject("Select Detector:", "Detector Selection",
    // XRayDetector.class);
    // detector.configure();
    detector = Configuration.getGlobalConfiguration().getDetector();
    detector.init();
    phantom = UserUtil.queryPhantom("Select Phantom", "Select Phantom");
    Material mat = null;

    do {
      String materialstr = UserUtil.queryString("Enter Background Medium:", "vacuum");
      mat = MaterialsDB.getMaterialWithName(materialstr);
    } while (mat == null);

    phantom.setBackground(mat);
    phantom.configure();

    rayTracer.setScene((PrioritizableScene) phantom);
    environment.setMaterial(phantom.getBackgroundMaterial());
    super.configure();
  }
  public Grid2D raytraceScene(PrioritizableScene phantomScene, Projection projection) {
    Trajectory geom = Configuration.getGlobalConfiguration().getGeometry();
    // Grid2D slice = new Grid2D(geom.getDetectorWidth(), geom.getDetectorHeight());
    Grid2D slice =
        detector.createDetectorGrid(geom.getDetectorWidth(), geom.getDetectorHeight(), projection);
    rayTracer.setScene(phantomScene);
    // Second rule of optimization is: Optimize later.
    PointND raySource = new PointND(0, 0, 0);
    raySource.setCoordinates(projection.computeCameraCenter());
    StraightLine castLine = new StraightLine(raySource, new SimpleVector(0, 0, 0));

    SimpleVector centerPixDir = null;
    if (accurate) {
      centerPixDir = projection.computePrincipalAxis();
    }
    // SimpleVector prinpoint = trajectory.getProjectionMatrix(sliceNumber).getPrincipalPoint();

    double xcorr = 0; // trajectory.getDetectorWidth()/2 - prinpoint.getElement(0);
    double ycorr = 0; // trajectory.getDetectorHeight()/2 - prinpoint.getElement(1);

    double length = trajectory.getSourceToDetectorDistance();
    Edge environmentEdge = new Edge(new PointND(0), new PointND(length));

    ArrayList<PhysicalObject> fallBackBackground = new ArrayList<PhysicalObject>(1);
    SimpleVector pixel = new SimpleVector(0, 0);
    boolean negate = false;
    for (int y = 0; y < trajectory.getDetectorHeight(); y++) {
      for (int x = 0; x < trajectory.getDetectorWidth(); x++) {
        pixel.setElementValue(0, x - xcorr);
        pixel.setElementValue(1, y - ycorr);
        SimpleVector dir = projection.computeRayDirection(pixel);
        if ((y == 0) && (x == 0)) {
          // Check that ray direction is towards origin.
          double max = 0;
          int index = 0;
          for (int i = 0; i < 3; i++) {
            if (Math.abs(dir.getElement(i)) > max) {
              max = Math.abs(dir.getElement(i));
              index = i;
            }
          }
          double t = -raySource.get(index) / dir.getElement(index);
          if (t < 0) negate = true;
        }
        if (negate) dir.negate();
        castLine.setDirection(dir);

        ArrayList<PhysicalObject> segments = rayTracer.castRay(castLine);
        if (accurate) {
          double dirCosine = SimpleOperators.multiplyInnerProd(centerPixDir, dir);
          length = trajectory.getSourceToDetectorDistance() / dirCosine;
        }

        if (segments == null) {
          fallBackBackground.clear();
          segments = fallBackBackground;
        } else {
          if (accurate) {
            environmentEdge =
                new Edge(new PointND(0), new PointND(length - getTotalSegmentsLength(segments)));
          }
        }
        environment.setShape(environmentEdge);
        segments.add(environment);
        /* old code:
        double integral = absorptionModel.evaluateLineIntegral(segments);

        slice.putPixelValue(x, y, integral);
         */
        detector.writeToDetector(slice, x, y, segments);
      }
    }
    return slice;
  }