Aerial multi-camera systems: Accuracy and block triangulation issues

Rupnik, Ewelina; Nex, Francesco; Toschi, I.; Remondino, Fabio

doi:10.1016/j.isprsjprs.2014.12.020

Cited by 81 publications

(82 citation statements)

References 25 publications

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“…If their footprints overlap with the one of the nadir camera, then the combined footprint resembles the shape of a Maltese cross, which has given those systems their name. (Rupnik et al, 2015) show the importance of flight planning for ensuring proper coverage with oblique camera systems of urban canyons, and they demonstrate both with simulations and evaluations of real data that the increased redundancy and the larger intersection angles improve the triangulation precision at the object, especially in the vertical direction.…”

Section: Introductionmentioning

confidence: 79%

Efficient Orientation and Calibration of Large Aerial Blocks of Multi-Camera Platforms

Karel¹,

Ressl²,

Pfeifer³

2016

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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KEY WORDS: multi-sensor calibration, oblique aerial imagery, tie point decimation, bundle block adjustment, affine-invariant feature point ABSTRACT:Aerial multi-camera platforms typically incorporate a nadir-looking camera accompanied by further cameras that provide oblique views, potentially resulting in utmost coverage, redundancy, and accuracy even on vertical surfaces. However, issues have remained unresolved with the orientation and calibration of the resulting imagery, to two of which we present feasible solutions. First, as standard feature point descriptors used for the automated matching of homologous points are only invariant to the geometric variations of translation, rotation, and scale, they are not invariant to general changes in perspective. While the deviations from local 2D-similarity transforms may be negligible for corresponding surface patches in vertical views of flat land, they become evident at vertical surfaces, and in oblique views in general. Usage of such similarity-invariant descriptors thus limits the amount of tie points that stabilize the orientation and calibration of oblique views and cameras. To alleviate this problem, we present the positive impact on image connectivity of using a quasi affine-invariant descriptor. Second, no matter which hard-and software are used, at some point, the number of unknowns of a bundle block may be too large to be handled. With multi-camera platforms, these limits are reached even sooner. Adjustment of sub-blocks is sub-optimal, as it complicates data management, and hinders self-calibration. Simply discarding unreliable tie points of low manifold is not an option either, because these points are needed at the block borders and in poorly textured areas. As a remedy, we present a straight-forward method how to considerably reduce the number of tie points and hence unknowns before bundle block adjustment, while preserving orientation and calibration quality.

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Section: Introductionmentioning

confidence: 79%

Efficient Orientation and Calibration of Large Aerial Blocks of Multi-Camera Platforms

Karel¹,

Ressl²,

Pfeifer³

2016

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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“…Multiple image measurements also utilize another significant aspect of oblique aerial images. Because of the convenient ray intersection angle, the measurement performed on images with a tilt angle of 45 degrees should be equally accurate in both the horizontal and vertical dimension (Rupnik et al, 2015).…”

Section: Multi Imagementioning

confidence: 99%

Accuracy of Measurements in Oblique Aerial Images for Urban Environment

Ostrowski

2016

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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ABSTRACT:Oblique aerial images have been a source of data for urban areas for several years. However, the accuracy of measurements in oblique images during this time has been limited to a single meter due to the use of direct -georeferencing technology and the underlying digital elevation model. Therefore, oblique images have been used mostly for visualization purposes. This situation changed in recent years as new methods, which allowed for a higher accuracy of exterior orientation, were developed. Current developments include the process of determining exterior orientation and the previous but still crucial process of tie point extraction. Progress in this area was shown in the ISPRS/EUROSDR Benchmark on Multi-Platform Photogrammetry and is also noticeable in the growing interest in the use of this kind of imagery. The higher level of accuracy in the orientation of oblique aerial images that has become possible in the last few years should result in a higher level of accuracy in the measurements of these types of images.The main goal of this research was to set and empirically verify the accuracy of measurements in oblique aerial images. The research focused on photogrammetric measurements composed of many images, which use a high overlap within an oblique dataset and different view angles. During the experiments, two series of images of urban areas were used. Both were captured using five DigiCam cameras in a Maltese cross configuration. The tilt angles of the oblique cameras were 45 degrees, and the position of the cameras during flight used a high grade GPS/INS navigation system. The orientation of the images was set using the Pix4D Mapper Pro software with both measurements of the in-flight camera position and the ground control points (measured with GPS RTK technology). To control the accuracy, check points were used (which were also measured with GPS RTK technology).As reference data for the whole study, an area of the city-based map was used. The archived results were referred to image orientation accuracy and to the ground sampling distance of the used images. The results show that the recent development of image orientation methods for oblique aerial images allow these images to be used for high quality photogrammetric measurements.

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“…In recent years interesting studies have been published on the proposed methods for oblique image orientation Rupnik et al 2015, using existing algorithms such as SIFT, or proposed new algorithms dedicated to matching oblique images. Searching for ways to improve automatic aerial triangulation for oblique images Yang et al (2012) proposed a multi-stage algorithm based on SIFT matching.…”

Section: * Corresponding Authormentioning

confidence: 99%

Towards Efficiency of Oblique Images Orientation

Ostrowski

Bakuła

2016

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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ABSTRACT:Many papers on both theoretical aspects of bundle adjustment of oblique images and new operators for detecting tie points on oblique images have been written. However, only a few achievements presented in the literature were practically implemented in commercial software. In consequence often aerial triangulation is performed either for nadir images obtained simultaneously with oblique photos or bundle adjustment for separate images captured in different directions. The aim of this study was to investigate how the orientation of oblique images can be carried out effectively in commercial software based on the structure from motion technology. The main objective of the research was to evaluate the impact of the orientation strategy on both duration of the process and accuracy of photogrammetric 3D products. Two, very popular software: Pix4D and Agisoft Photoscan were tested and two approaches for image blocks were considered. The first approach based only on oblique images collected in four directions and the second approach included nadir images. In this study, blocks for three test areas were analysed. Oblique images were collected with medium-format cameras in maltan cross configuration with registration of GNSS and INS data. As a reference both check points and digital surface models from airborne laser scanning were used.

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Aerial multi-camera systems: Accuracy and block triangulation issues

Cited by 81 publications

References 25 publications

Efficient Orientation and Calibration of Large Aerial Blocks of Multi-Camera Platforms

Efficient Orientation and Calibration of Large Aerial Blocks of Multi-Camera Platforms

Accuracy of Measurements in Oblique Aerial Images for Urban Environment

Towards Efficiency of Oblique Images Orientation

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