Standards and specifications for the calibration and stability of amateur digital cameras for close-range mapping applications

Abstract

Photogrammetry is concerned with the accurate derivation of spatial and descriptive information from imagery that can be used in several applications such as mapping, DEM generation, orthophoto production, construction planning, environmental monitoring, structural analysis, 3D visualization, and change detection. The type of cameras traditionally used for high accuracy projects were large format analogue cameras. In recent years, however, the use of digital cameras for photogrammetric purposes has become more prevalent. The switch by some users from analogue to digital cameras has been fuelled by the ease of use, decreasing cost, and increasing resolution of digital cameras. Digital photogrammetric cameras can be classified into several categories: line cameras (e.g., ADS40 from Leica Geosystems), large format frame cameras (e.g., DMC TM from Zeiss/Intergraph), and medium to small-format digital cameras. More recently, amateur medium-format digital cameras (MFDC) and small-format digital cameras (SFDC) are being used in photogrammetric activities (e.g., in conjunction with LiDAR systems, smaller flight blocks, and for close-range photogrammetric applications). The continuing development in the capabilities of digital photogrammetry coupled with users’ needs has spawned new markets in photogrammetric mapping with amateur digital cameras. With the wide spectrum of designs for amateur digital cameras, several issues have surfaced, including the method and quality of camera calibration, as well as long-term stability. This paper addresses these concerns and outlines possible solutions. First, we will start by introducing an automated methodology for an in-door camera calibration. The main objective of such a procedure is to provide mapping companies using these cameras with a simple calibration procedure that requires an easy-to-establish test field. The paper will then discuss the concept of how to evaluate camera stability, which will be followed by the introduction of a set of tools for its evaluation. Following the discussion on calibration and stability analysis, the paper will deal with several related questions: How to develop meaningful standards for evaluating the outcome from the calibration procedure; How to develop meaningful standards for evaluating the stability of the involved camera; Is there a flexibility in choosing the stability analysis tool based on the geo-referencing procedure; Can the stability analysis be used for evaluating the equivalency of different distortion models. Finally, experimental results are then provided for two small format digital cameras.