Coordinate Systems

The coordinates used in the program do not always refer to a same coordinate system. The type of coordinate system is mentioned each time. The following coordinate systems are used:


Camera Coordinate System

The fiducial marks on a photograph render a unalterable coordinate system on each photograph. The origin of the coordinate system, called the fiducial center, is the geometric center of the photograph and the X- and Y-axes are parallel to the edges of the photograph. The fiducial point coordinates are available on the calibration certificate of the camera, and define a stable camera coordinate system.

Each point of the photograph can be expressed in this coordinate system. The coordinates are expressed in millimeter. The camera coordinates of tiepoints are independent of any rotated view on the photograph, since the camera coordinates are expressed only relative to the fiducial marks.

Image Coordinate System:

This is the coordinate system of the raw image as seen in a 'Tiepoint Window'. The origin of the system is the left bottom corner of the file.
The Y- axis is vertical and the X-axis horizontal. The units of the system are numbers of pixels. Each pixel in the image can then be expressed in positive X- and Y-coordinates.

The image coordinates for a rotated file are not the same as these for a not rotated file. They are expressed in a rotated image system. The origin of the coordinate system will be in both cases in the left bottom corner.

Image coordinates saved in the project file are expressed in this image coordinate system taking into account the used rotation.

Terrain Coordination System

The terrain coordinate system is the coordinate system used to express the X-, Y- and Z-coordinates of object points, control points, and projection centers. This coordinate system can be arbitrarily chosen by the user and defined by a “Projection” (see OrbitGIS). It is however necessary that all points are expressed in the same coordinate system throughout the entire project.

The units used are displayed by default in meter. It is up to the user to interprete the coordinates referenced to another terrain system unit.