Step2 : Setting the camera parameters

2.0 Define a Camera

Modeller is designed to work with any make of digital camera. Before building a model it is necessary to provide details of the camera being used.

You can use the Tools->Wizards->Camera Wizard to have a Wizard direct you through the process of defining a camera. This is recommended for new users.

Alternatively you can set up the camera using the project settings. Open the Project->Settings... dialog box, and select the Camera tab. The following property page is displayed,

Define the Camera Type in one of the following ways - please note that if you wish to use Viewpoint Estimation in the project you must not set the camera type to None

You do not wish to use viewpoint estimation, but instead will be providing the viewing directions. Choose None, you do not need to describe your camera for this kind of project.
The camera is a supported camera, select the Choose option and then select it's name from the list box, by double clicking the left mouse button. If the camera type chosen has a zoom lense, then set the Zoom level slider to specify the zoom setting you will be using. If you are unable to estimate the camera's zoom settings then use the camera fully zoomed out or fully zoomed in, and set the slider to one end. Alternatively you can calibrate the camera (see 2 below). If the camera supports more than one image size then choose the size you will be using from the Image Size combination box. Note that supported cameras are defined in files stored in the installation's Cameras directory. This allows further cameras to be added to the list at a later date, check the Online Forum for further supported cameras.
Your camera is not supported and you do not know the required information, or you have a zoom-camera but can not estimate the zoom setting. If you want to use Viewpoint Estimation in the project you must calibrate the camera. Add a calibration image to the project (see below) and then select the Calibrate option. Follow the instructions below.
The camera is not supported but you know all the camera details required, you can define a Custom Camera. Select Custom, and fill in the details in the edit boxes in the custom camera group. The meaning of these parameters is explained here.

2.1 Adding a calibration image to a project

A Calibration Image is used to infer details about your camera. In order to do this an image is required of an object of known size, a known distance away. The following approach is recommended,

Place two small objects (such as coins) on a table or other flat surface, 1 meter apart and 1 meter away from the edge of the table, as in Figure 1.0.
Holding the camera close to the edge of the table, with it as close as possible to the table top, take a picture that includes both objects.

Figure 1.0

If your camera cannot view both objects at once, the objects may be placed any distance apart (the Target Width), and any distance away (the Distance to Target) from the table edge. Remember the two distances you choose, the program requires these two numbers.

Now load the image into the project. View the image and select View->Properties from the menu. From the dialog box, select Use this image for calibration, as shown below,

Select Calibration Properties, the following dialog box appears,

enter the Distance to target D (this is the distance that the objects are from the edge of the table), and Width of target W (this is the distance the objects are apart), as shown in Figure 1.0 .

Now define a viewpoint cue for this image. Select the Viewpoint Cue button on the image tool-bar. Using the mouse select the position in the image of each of the two objects placed on the table.

Open the Project->Settings... dialog box, and select the Camera tab. Select the Calibrate option.

2.2 Defining a Custom Camera

To define a Custom Camera select Project->Settings->Camera Tab and then select the Custom radio button.

Fill in the values in the Custom Camera group. To understand the meaning of these values consider the camera geometry shown in Figure 2.0. Here an object point Q forms an image on the image plane at q. The width of the image plane in millimeters is the value of CCD Width, as the CCD is the part of a digital camera on which images are formed. Similarly the height of this plane corresponds to CCD Height. The camera's CCD is a rectangular array of Pixels (picture elements), arranged in a grid. The width and Height of this grid correspond to the Width and Height parameters.

The image, q, of point Q is formed by a 'ray' passing through Q and f, intersecting the image plane. The point f lies perpendicularly behind the image plane point c, the image centre, a distance of Focal Length millimeters. The focal length corresponds to the camera's zoom.

As focal length is increased the image of the object will become larger, this is equivalent to using camera zoom to make things look bigger. Increasing the focal distance also reduces perspective effect, so lines which are parallel in reality look parallel in the image.

Finally note that the image origin is at the top-left of the image plane.

Figure 2.0