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Due to the fixed length and short distance of the existing length reference ruler in the digital industrial photogrammetry system, it is difficult to meet the measurement of large-size components. This article proposes a variable-length reference ruler construction method. Firstly, a tooling suitable for total station and photogrammetry is developed, and the tooling is placed at the two ends of the largest dimension of the component to be tested. The maximum actual length of the component is measured by the total station, the point coordinates with the non-real size length of the component is obtained by photogrammetry. Then, the three-dimensional coordinates of all points with the actual scale factor are obtained, by bringing the actual size measured by the total station into the photogrammetric calculation model, and the calibrated size of the tooling itself can be used to verify the accuracy of the length reference measurement of this method. At last, it is verified through examples that the variable-length reference ruler construction method of this article overcomes the shortcomings of the existing photogrammetric system’s own length reference ruler, it provides an effective way to carry out convenient and efficient high-precision measurement of large-size components, and improves the on-site adaptability of the photogrammetric system.
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