Step 4 : Define Viewing Directions

4.0 Defining Viewing Directions

Each View must be associated with a Viewing Direction. These are either supplied by you or calculated automatically.

Select an image and press the right mouse button to view it's properties. The following dialog is displayed,

The image's viewpoint is defined in the Viewing Direction group of this dialog.

For images from digital cameras, that contain a Viewpoint Target, a viewpoint can be calculated automatically, using Viewpoint Estimation. The Calculate Viewing Direction From Cue radio button must be selected.

For other images the Viewing Direction must be provided. Select the Provide Viewing Direction radio button and then press the Viewing Direction button to display the viewing direction settings, these are shown below,

The image on the left shows a series of Standard Viewpoints, such as Front, Back, Left, Top etc. These are shown relative to the Global Coordinate System XYZ in which the XY plane would usually be the surface on which the object(s) are resting. Choose the viewpoint which corresponds to the viewing orientation of this image.

The preview image on the right shows a preview of the viewing direction you have selected. This is a view of a 3D model seen from the viewing direction you supply.

The range of possible viewing directions is widened by defining a Roll Angle, this is a rotation of the viewing direction about the line of sight. For example photos are very often taken in what is called a Portrait Style with the camera tilted through 90 degrees clockwise or anti clockwise. This corresponds to a Roll Angle of +90 or -90 degrees respectively.

For complete control over viewing direction select the More button. This will display the following extra controls,

The viewing direction defined so far can be further adjusted by rotation about the three coordinate system axis. The rotation of the viewing direction is defined by three angles (in degrees), these are called RotationX, RotationY and RotationZ. The viewing direction is rotated clockwise around the X axis by RotationX degrees, then around the Y axis by Rotation Y degrees, and finally around the Z axis by RotationZ degrees.

4.3 Using mixed viewing directions

Projects may contain some images with Calculated Viewing Directions and some with Provided Viewing Directions If the project contains one or more images with an automatically calculated viewpoint (from a Viewpoint Cue), then the Global Coordinate System is aligned with the Viewpoint Target.

The image on the left of the Viewing Direction dialog shows the details of the alignment of the Global Coordinate System XYZ and the Viewpoint Target.

A Front view is one looking at the Front-edge of the Viewpoint Target, a Top view looks directly down on the Viewpoint Target, and a back view looks at the Back-Edge. The Back-edge of the Viewpoint Cue is coloured blue to distinguish it from the other edges. When defining the Viewpoint Cue the back edge is the starting edge.

4.3 Viewing Positions

Modeller calculates viewing positions for each view. It does this based on the viewing direction for that view, and the silhouettes it contains.

Modeller will choose viewing positions so that silhouettes in the smallest common group are best aligned. This means that group 0 (the default group) is used to align two views whenever they both contain silhouettes in group 0, if not then group 1 is tried next - and so on. If you do not wish Modeller to use a particular silhouette in this process de-select the Include in viewpoint definition, in the silhouette's properties.