CALIBRATION STUDY OF A TRIMBLE ACx4 SYSTEM FOR DIRECT GEOREFERENCING MAPPING APPLICATIONS

L E Filho,E A Mitishita

doi:10.5194/isprs-annals-iv-1-45-2018

Abstract

Abstract. The Trimble Aerial Camera x4 (i.e., TACx4) is a photogrammetric multi-head system manufactured by Trimble Inc.© in 2010. It has four cameras mounted together in the main structure allowing the simultaneous acquisition to generate a single synthetic image with much larger ground coverage. In addition, the cameras are also integrated with a GNSS/INS to perform “Direct” or “Integrated” Sensor Orientation. The main condition to obtain photogrammetric mapping products with high accuracy using a direct sensor orientation procedure is to execute a step known as “geometric system calibration”. In general, the photogrammetric multi-head system manufacturers perform this step using laboratory methods to obtain the parameters of cameras interior and relative orientation. Accurate mounting parameters (lever arms and “boresight misalignments”) are fundamental requirements to generate the synthetic image when georeferencing of images is applied. This paper shows a “full field” calibration method to perform the geometric system calibration of the TACx4 system and its evaluation for direct sensor orientation mapping applications. The developed method involves two steps using only aerial images: (1) estimation of the cameras interior and relative orientation parameters to generate the synthetic image and (2) estimation of the synthetic image interior orientation and the mounting parameters between the synthetic image and GNSS/INS reference systems using two different methods. The obtained results in the conventional photogrammetric project show that the proposed method allows performing the geometric system calibration of the TACx4 system achieving around 50 cm (5 pixels) in horizontal and vertical accuracies. The obtained results can be used for large-scale mapping requirements using direct sensor orientation according to Brazilian accuracy standards.

Highlights

In conventional aerial photogrammetric mapping projects, the exterior orientation parameters of a block of images have been indirectly determined by the bundle block adjustment using collinearity equations and ground control points
Due to the GNSS/INS integration technologies, the Direct Sensor Orientation has been frequently used to perform the direct georeferencing of images, reducing the cost and time involved to establish a set of control points at the ground
In the “Single-Step” method, the mounting parameters and the interior orientation parameters are considered as unknowns in a bundle block adjustment that incorporates the position and orientation information derived from the GNSS/INS trajectory using the mathematical model presented in equation (15)

Summary

INTRODUCTION

In conventional aerial photogrammetric mapping projects, the exterior orientation parameters of a block of images have been indirectly determined by the bundle block adjustment using collinearity equations and ground control points. Additional optical cones produce color image separated in red, green, blue and near-infrared In this year, the authors shown the potential of the UCD camera system for mapping applications and its geometric calibration process using laboratory methods for the virtual image generation (Leberl et al, 2003). In 2002 and 2004, the authors investigated the direct geo-referencing of sensors based at a combination of relative kinematic GPS-positioning and inertial measurement units (IMU) with high accuracy level and discussed the aspects of Camera/IMU boresight calibration as a critical element in the mapping process when using GPS/IMU in the direct georeferencing mode of mapping (Mostafa, 2002 and Jacobsen, 2004). In the two-step method, the mounting parameters are determined by comparing the GNSS/INS position and orientation information at the image acquisition time and the corresponding camera EOP (Exterior Orientation Parameters) obtained from the traditional bundle block adjustment using ground control points.

THE CALIBRATION METHOD

Data used for calibration

Findings

CONCLUSIONS