A photogrammetric surveying method for field applications

Abstract

AbstractA photogrammetric method is presented for mapping rock outcrops and other objects in the field. Special attention was paid to simplifying the workflow and to minimising extra bulk and weight of the required equipment while maximising the accuracy of the survey. The minimum equipment needed for the surveys added less than 0·5 kg to the backpack of a field scientist, or as little as 0·2 kg assuming that a suitable camera was already part of the typical equipment carried in the field. Data acquisition in the field took less than 15 min, while image orientation and preparation for stereoviewing took less than 30 min even for a user with little training. Best results were accomplished taking two convergent images as well as three images parallel to the object of interest. Two test sites were surveyed with the method, covering volumes of 3·5 × 5 × 3 m3 and 18 × 20 × 5 m3, to identify the most accurate adjustment method. The maximum length measurement error (LME) was calculated for 28 and 78 distances in the smaller and larger volume, respectively, based on a comparison of the photogrammetric survey with an independent total station survey of the same signalised points. The maximum LME ranged between 0·005 and 0·002 m for the first test site where three cameras were tested, and was 0·021 m for the larger test site where only one camera was tested. The rmse values of the LMEs ranged between 0·003 and 0·001 m for the first and 0·010 m for the second test site, respectively. The smallest and lightest camera, a Ricoh GR Digital, yielded the most accurate results in object space when interior orientation was calibrated on the job. The Sigma SD14 did not require on‐the‐job calibration for accurate results and was the camera with the best geometric stability. The third camera evaluated, a Rollei d7 metric5, also yielded good results, but could not deliver the extra value that would be expected from a metric camera designed for photogrammetric surveys.