Geometric Calibration of Thermal Cameras

Geometric Calibration of Thermal Cameras. This paper discusses strategies, tools and methods for the geometric calibration of closerange thermal cameras as they are widely used for building monitoring and material testing. Two different testfields have been developed and tested whereby each of them provides target points in the thermal spectrum. Four different cameras with solid-state imaging sensors have been calibrated. In general, all lenses show relatively large distortions due to decentering of lenses and non-orthogonality of the image coordinate system. Using a 2D testfield with burning lamps an accuracy of 0.3 pixels can be achieved while a 3D testfield with reflective circular targets provides residuals in the order of 0.05 pixels. This leads to geometrically improved thermal images that can be used to achieve higher quality for various applications, such as mosaicking, 3D-texturing or pan sharpening.