February 2007 | Q & A
How are SOCET SET image coordinates defined?
Coordinate Measurement window
SOCET SET image coordinates are expressed as an ordered pair of double precision, floating point numbers which identify a row (line) and column (sample) location within the matrix of pixels. The SOCET SET image coordinate values can be seen on the Coordinate Measurement window, or within measurement files from triangulation (*.ipf) and interior orientation (*.iop).
The origin, position (0,0), to which the line and sample values are referenced is defined as half of the total number of lines and half of the total number of samples measured from the center of the upper left pixel. This means that the origin of the image coordinate system may fall inside a pixel or on the boundary between pixels depending on whether the number of lines and samples is even or odd, respectively. Also it should be noted that the origin will be near the center of the image, not exactly at the center. The origin will be one half pixel down and to the right of the actual image center.
Figure 1. Even number of lines and samples, origin inside a pixel.
Figure 2. Odd number of lines and samples, origin at pixel boundary.
Positive line coordinates are measured downward from the origin and positive sample coordinates are to the right of the origin. Lines above the origin are negative as are samples to the left of the origin. The figure below shows some example image locations and their line and sample values in the SOCET SET image coordinate system. See Sensor Model section of the SOCET SET programmer’s reference for more detail.
Figure 3. Point, line and sample results
Point, line, and sample results
Note to Developers: When integrating SOCET SET with other applications where image coordinates are being passed back and forth, it is the calling application’s responsibility to convert the image coordinates to/from SOCET SET coordinates, origin as described above, and the coordinate system used by the other application — most likely origin at the upper left hand corner.
Tags: SOCET SET