scholarly journals Camera Calibration using the Damped Bundle Adjustment Toolbox

2014 ◽  
Vol II-5 ◽  
pp. 89-96 ◽  
Author(s):  
N. Börlin ◽  
P. Grussenmeyer
Keyword(s):  
Camera Calibration ◽  
Focal Length ◽  
Standard Procedure ◽  
Calibration Procedure ◽  
Bundle Adjustment ◽  
Data Sets ◽  
Calibration Data ◽  
Initial Values ◽  
Convergence Results ◽  
Highly Correlated

Camera calibration is one of the fundamental photogrammetric tasks. The standard procedure is to apply an iterative adjustment to measurements of known control points. The iterative adjustment needs initial values of internal and external parameters. In this paper we investigate a procedure where only one parameter &ndash; the focal length is given a specific initial value. The procedure is validated using the freely available Damped Bundle Adjustment Toolbox on five calibration data sets using varying narrow- and wide-angle lenses. <br><br> The results show that the Gauss-Newton-Armijo and Levenberg-Marquardt-Powell bundle adjustment methods implemented in the toolbox converge even if the initial values of the focal length are between 1/2 and 32 times the true focal length, even if the parameters are highly correlated. Standard statistical analysis methods in the toolbox enable manual selection of the lens distortion parameters to estimate, something not available in other camera calibration toolboxes. <br><br> A standardised camera calibration procedure that does not require any information about the camera sensor or focal length is suggested based on the convergence results. <br><br> The toolbox source and data sets used in this paper are available from the authors.

scholarly journals CAMERA CONSTANT IN THE CASE OF TWO MEDIA PHOTOGRAMMETRY

2015 ◽  
Vol XL-5/W5 ◽  
pp. 1-6 ◽  
Author(s):  
P. Agrafiotis ◽  
A. Georgopoulos
Keyword(s):  
Refractive Index ◽  
Camera Calibration ◽  
Focal Length ◽  
Calibration Procedure ◽  
Water Salinity ◽  
Clean Water ◽  
Object Distance ◽  
Calibration Methods ◽  
The One ◽  
Probable Relation

Refraction is the main cause of geometric distortions in the case of two media photogrammetry. However, this effect cannot be compensated and corrected by a suitable camera calibration procedure (Georgopoulos and Agrafiotis, 2012). In addition, according to the literature (Lavest et al. 2000), when the camera is underwater, the effective focal length is approximately equal to that in the air multiplied by the refractive index of water. This ratio depends on the composition of the water (salinity, temperature, etc.) and usually ranges from 1.10 to 1.34. It seems, that in two media photogrammetry, the 1.33 factor used for clean water in underwater cases does not apply and the most probable relation of the effective camera constant to the one in air is depending of the percentages of air and water within the total camera-to-object distance. This paper examines this relation in detail, verifies it and develops it through the application of calibration methods using different test fields. In addition the current methodologies for underwater and two-media calibration are mentioned and the problem of two-media calibration is described and analysed.

scholarly journals THE DATABASE FOR MULTIFACTORIAL UAV ACCURACY ASSESSMENTS

2020 ◽  
Vol XLIII-B5-2020 ◽  
pp. 163-172
Author(s):  
P. Wiącek
Keyword(s):  
Camera Calibration ◽  
Statistical Models ◽  
A Priori ◽  
Bundle Adjustment ◽  
Data Sets ◽  
Test Field ◽  
Exterior Orientation ◽  
Multiple Factors ◽  
Adjustment Processes ◽  
Accuracy Assessments

Abstract. Due to the increasing range of work carried out with UAV in recent years, the importance of final product accuracy appreciates. However, obtaining survey-grade accuracy requires to perform bundle adjustment processes that could be affected by multiple factors like unstable camera calibration, a correlation between interior and exterior orientation, insufficient georeferenced information, and software settings. During the project, multi-variant flight over the test field was conducted. The flights were performed with a fixed-wing airframe equipped with PPK receiver on-board. Based on the conducted flights, the database for multifactorial data sets has been prepared. The database containing hundreds of independent adjustment variants which differ as follows: georeferencing method, flight configuration, additional camera calibration corrections, tie points filtering, and a priori accuracy settings. The database allowed to investigate the separate influence of each factor on the final results using ANOVA statistical models.

A Comparison of Two Different Approaches to Camera Calibration in LSDM Photogrammetric Systems

2014 ◽  
Author(s):  
Ou Bai ◽  
Fiorenzo Franceschini ◽  
Maurizio Galetto ◽  
Luca Mastrogiacomo ◽  
Domenico A. Maisano
Keyword(s):  
Camera Calibration ◽  
Large Scale ◽  
Focal Length ◽  
Calibration Procedure ◽  
Optical Systems ◽  
Multiple Cameras ◽  
Dimensional Metrology ◽  
Distortion Parameters ◽  
Length Distortion

Large Scale Dimensional Metrology (LSDM) is a branch of metrology that deals with the measurement of objects with dimensions in the order of several meters. Optical systems, relying on the use of multiple cameras and photogrammetric techniques, are among the most used instruments in this field. These systems require a preliminary calibration procedure to determine some essential parameters, such as camera positions and orientations, focal length, distortion parameters, etc. A structured comparison between two different approaches to camera calibration is herein discussed.

scholarly journals Orthoimages of the outer walls and towers of the château de Chambord

2015 ◽  
Vol II-5/W3 ◽  
pp. 243-250
Author(s):  
A. Pinte ◽  
R. Héno ◽  
M. Pierrot-Deseilligny ◽  
X. Brunetaud ◽  
S Janvier-Badosa ◽  
...  
Keyword(s):  
Focal Length ◽  
Meteorological Data ◽  
Ground Level ◽  
Bundle Adjustment ◽  
Data Sets ◽  
French Renaissance ◽  
Gis Applications ◽  
Focal Length Lens ◽  
World Heritage List ◽  
Visualization Of Data

The <i>château de Chambord</i> is one of the most famous castles in the world as it is an emblem of French Renaissance architecture. It was built at the beginning of the 16<sup>th</sup> century and has been part of the UNESCO World Heritage list since 1981. The monitoring of such a monument involves the organization and visualization of data sets such as archive documents, survey data, scientific documentation, restoration reports, meteorological data, etc. This process requires the realization of a support for documentation which may be an orthoimage. A photogrammetric survey was recently performed, in the framework of the traditional fieldwork of the students in the PPMD master's degree (Specialized Master’s in Positionning, Photogrammetry and Deformation Measurement) at the French National School of Geographic Sciences (ENSG). High resolution images were taken from the ground level, using two off-the-shelf reflex cameras, equipped with a 35 mm, a 100 mm and a 200 mm focal length lens according to the needs. The MicMac software was used for the bundle adjustment, the georeferencing and the dense correlation procedures, including orthoimage calculation. Added to plane-based orthoimages, cylinder-based orthoimages were generated for the 2D representation of the outer walls of the château de Chambord including façades and towers. Fitting the 2D projection to the mean characteristics of the geometry has a promising documentation potential for GIS applications in heritage studies.

scholarly journals THE TEST FIELD FOR UAV ACCURACY ASSESSMENTS

2019 ◽  
Vol XLII-1/W2 ◽  
pp. 67-73
Author(s):  
P. Wiącek ◽  
K. Pyka
Keyword(s):  
Camera Calibration ◽  
Bundle Adjustment ◽  
Common Method ◽  
Data Sets ◽  
Test Field ◽  
Exterior Orientation ◽  
Multiple Factors ◽  
Adjustment Processes ◽  
Flight Direction ◽  
Accuracy Assessments

<p><strong>Abstract.</strong> Nowadays UAV photogrammetry becomes a common method for mapping and surveying. At the same time due to the increasing range of work carried out with UAV, the importance of final product accuracy increases. However to obtain survey-grade accuracy it is necessary to perform bundle adjustment processes that could be affected by multiple factors like unstable camera calibration, correlation between interior and exterior orientation and insufficient georeference information. One of the aims of the project was to prepare the terrestrial test field, which helps to obtain optimal decorrelation and allows to objectively assess the accuracy of the bundle adjustment in UAV application. During the project, two multi-variant flights over the test field were conducted. The flights were performed with a fixed-wing airframe equipped with PPK receiver on-board. Based on the conducted flights, many data sets have been prepared, which differ as follows: types of cameras, GSD, flight direction and georeferenced method.</p>

scholarly journals Impact of Stereo Camera Calibration to Object Accuracy in Multimedia Photogrammetry

2020 ◽  
Vol 12 (12) ◽  
pp. 2057
Author(s):  
Oliver Kahmen ◽  
Robin Rofallski ◽  
Thomas Luhmann
Keyword(s):  
Camera Calibration ◽  
Standard Procedure ◽  
Relative Orientation ◽  
Bundle Adjustment ◽  
Underwater Imaging ◽  
Stereo Camera ◽  
Positioning Errors ◽  
Systematic Effects ◽  
Set Up ◽  
Implicit Modelling

Camera calibration via bundle adjustment is a well-established standard procedure in single-medium photogrammetry. When using standard software and applying the collinearity equations in multimedia photogrammetry, the effects of refractive interfaces are compensated in an implicit form, hence by the usual parameters of interior orientation. This contribution analyses different calibration strategies for planar bundle-invariant interfaces. To evaluate the effects of implicitly modelling the refractive effects within bundle adjustment, synthetic error-free datasets are simulated. The behaviour of interior, exterior, and relative orientation parameters is analysed using synthetic datasets free of underwater imaging effects. A shift of the camera positions of 0.2% of the acquisition distance along the optical axis can be observed. The relative orientation of a stereo camera shows systematic effects when the angle of convergence varies. The stereo baseline increases by 1% at 25° convergence. Furthermore, the interface is set up at different distances to the camera. When the interface is at 50% distance assuming a parallel camera setup, the stereo baseline also increases by 1%. It becomes clear that in most cases the implicit modelling is not suitable for multimedia photogrammetry due to geometrical errors (scaling) and absolute positioning errors. Explicit modelling of the refractive interfaces is implemented into a bundle adjustment and is also used to analyse calibration parameters and deviations in object space. Real experiments show that it is difficult to separate the effects of implicit modelling, since other effects, such as poor image measurements, affect the final result. However, trends can be seen, and deviations are quantified.

scholarly journals Extrinsic Camera Calibration with Line-Laser Projection

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1091
Author(s):  
Izaak Van Crombrugge ◽  
Rudi Penne ◽  
Steve Vanlanduit
Keyword(s):  
Camera Calibration ◽  
Real World ◽  
Large Scale ◽  
State Of The Art ◽  
Bundle Adjustment ◽  
Field Of View ◽  
Extrinsic Calibration ◽  
Practical Procedure ◽  
Partial Overlap

Knowledge of precise camera poses is vital for multi-camera setups. Camera intrinsics can be obtained for each camera separately in lab conditions. For fixed multi-camera setups, the extrinsic calibration can only be done in situ. Usually, some markers are used, like checkerboards, requiring some level of overlap between cameras. In this work, we propose a method for cases with little or no overlap. Laser lines are projected on a plane (e.g., floor or wall) using a laser line projector. The pose of the plane and cameras is then optimized using bundle adjustment to match the lines seen by the cameras. To find the extrinsic calibration, only a partial overlap between the laser lines and the field of view of the cameras is needed. Real-world experiments were conducted both with and without overlapping fields of view, resulting in rotation errors below 0.5°. We show that the accuracy is comparable to other state-of-the-art methods while offering a more practical procedure. The method can also be used in large-scale applications and can be fully automated.

A Reliability-Based Approach to Assess Fatigue Behaviour Based on Small Incomplete Data Sets

2008 ◽  
Vol 44-46 ◽  
pp. 871-878 ◽  
Author(s):  
Chu Yang Luo ◽  
Jun Jiang Xiong ◽  
R.A. Shenoi
Keyword(s):  
Incomplete Data ◽  
Standard Procedure ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Small Sample ◽  
Data Sets ◽  
Safe Life ◽  
A New Technique ◽  
And Performance

This paper outlines a new technique to address the paucity of data in determining fatigue life and performance based on reliability concepts. Two new randomized models are presented for estimating the safe life and pS-N curve, by using the standard procedure for statistical analysis and dealing with small sample numbers of incomplete data. The confidence level formulations for the safe and p-S-N curve are also given. The concepts are then applied for the determination of the safe life and p-S-N curve. Two sets of fatigue tests for the safe life and p-S-N curve are conducted to validate the presented method, demonstrating the practical use of the proposed technique.

scholarly journals Simultaneous Robot–World and Hand–Eye Calibration without a Calibration Object

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3949 ◽  
Author(s):  
Wei Li ◽  
Mingli Dong ◽  
Naiguang Lu ◽  
Xiaoping Lou ◽  
Peng Sun
Keyword(s):  
Three Dimensional ◽  
Real Data ◽  
Medical Robotics ◽  
Calibration Method ◽  
Bundle Adjustment ◽  
Data Sets ◽  
Rigid Transformation ◽  
Validation Experiment ◽  
Dimensional Reconstruction ◽  
Sparse Bundle Adjustment

An extended robot–world and hand–eye calibration method is proposed in this paper to evaluate the transformation relationship between the camera and robot device. This approach could be performed for mobile or medical robotics applications, where precise, expensive, or unsterile calibration objects, or enough movement space, cannot be made available at the work site. Firstly, a mathematical model is established to formulate the robot-gripper-to-camera rigid transformation and robot-base-to-world rigid transformation using the Kronecker product. Subsequently, a sparse bundle adjustment is introduced for the optimization of robot–world and hand–eye calibration, as well as reconstruction results. Finally, a validation experiment including two kinds of real data sets is designed to demonstrate the effectiveness and accuracy of the proposed approach. The translation relative error of rigid transformation is less than 8/10,000 by a Denso robot in a movement range of 1.3 m × 1.3 m × 1.2 m. The distance measurement mean error after three-dimensional reconstruction is 0.13 mm.

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