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Oblique Airborne Photogrammetry: Users' and Vendors' View - EuroSDR Survey
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Today, oblique airborne images are a powerful source of geodata, particularly for applications in urban areas. Although the cost of capturing is higher, object identification and creation of dense 3D point clouds is easier and more reliable compared to conventional vertical imagery. To better understand the current practice and possible user needs, the EuroSDR initiated a survey on the use and expectations of obliques. The questionnaire went online in spring 2014 and was targeted at both users and providers of hardware, software and services. Here, the authors summarise the key findings from the survey.
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... Those images are used for instance for visualisation, identification of objects, 3D mapping and automatic building detection or verification (Frommholz et al., 2015, Remondino et al., 2016. A survey amongst users and vendors of airborne oblique camera systems, software developers and researchers was initiated by EuroSDR (Gerke and Remondino, 2014). It revealed that for geometric applications the standard photogrammetric products are still having deficits, especially regarding bundle block adjustment automation and accuracy (Rupnik et al., 2015). ...
During the last decade the use of airborne multi camera systems increased significantly. The development in digital camera technology allows mounting several mid- or small-format cameras efficiently onto one platform and thus enables image capture under different angles. Those oblique images turn out to be interesting for a number of applications since lateral parts of elevated objects, like buildings or trees, are visible. However, occlusion or illumination differences might challenge image processing. From an image orientation point of view those multi-camera systems bring the advantage of a better ray intersection geometry compared to nadir-only image blocks. On the other hand, varying scale, occlusion and atmospheric influences which are difficult to model impose problems to the image matching and bundle adjustment tasks. In order to understand current limitations of image orientation approaches and the influence of different parameters such as image overlap or GCP distribution, a commonly available dataset was released. The originally captured data comprises of a state-of-the-art image block with very high overlap, but in the first stage of the so-called ISPRS/EUROSDR benchmark on multi-platform photogrammetry only a reduced set of images was released. In this paper some first results obtained with this dataset are presented. They refer to different aspects like tie point matching across the viewing directions, influence of the oblique images onto the bundle adjustment, the role of image overlap and GCP distribution. As far as the tie point matching is concerned we observed that matching of overlapping images pointing to the same cardinal direction, or between nadir and oblique views in general is quite successful. Due to the quite different perspective between images of different viewing directions the standard tie point matching, for instance based on interest points does not work well. How to address occlusion and ambiguities due to different views onto objects is clearly a non-solved research problem so far. In our experiments we also confirm that the obtainable height accuracy is better when all images are used in bundle block adjustment. This was also shown in other research before and is confirmed here. Not surprisingly, the large overlap of 80/80% provides much better object space accuracy – random errors seem to be about 2-3fold smaller compared to the 60/60% overlap. A comparison of different software approaches shows that newly emerged commercial packages, initially intended to work with small frame image blocks, do perform very well.
... Those images are used for instance for visualisation, identification of objects, 3D mapping and automatic building detection or verification (Frommholz et al., 2015, Remondino et al., 2016. A survey amongst users and vendors of airborne oblique camera systems, software developers and researchers was initiated by EuroSDR (Gerke and Remondino, 2014). It revealed that for geometric applications the standard photogrammetric products are still having deficits, especially regarding bundle block adjustment automation and accuracy (Rupnik et al., 2015). ...
During the last decade the use of airborne multi camera systems increased significantly. The development in digital camera technology allows mounting several mid- or small-format cameras efficiently onto one platform and thus enables image capture under different angles. Those oblique images turn out to be interesting for a number of applications since lateral parts of elevated objects, like buildings or trees, are visible. However, occlusion or illumination differences might challenge image processing. From an image orientation point of view those multi-camera systems bring the advantage of a better ray intersection geometry compared to nadir-only image blocks. On the other hand, varying scale, occlusion and atmospheric influences which are difficult to model impose problems to the image matching and bundle adjustment tasks. In order to understand current limitations of image orientation approaches and the influence of different parameters such as image overlap or GCP distribution, a commonly available dataset was released. The originally captured data comprises of a state-of-the-art image block with very high overlap, but in the first stage of the so-called ISPRS/EUROSDR benchmark on multi-platform photogrammetry only a reduced set of images was released. In this paper some first results obtained with this dataset are presented. They refer to different aspects like tie point matching across the viewing directions, influence of the oblique images onto the bundle adjustment, the role of image overlap and GCP distribution. As far as the tie point matching is concerned we observed that matching of overlapping images pointing to the same cardinal direction, or between nadir and oblique views in general is quite successful. Due to the quite different perspective between images of different viewing directions the standard tie point matching, for instance based on interest points does not work well. How to address occlusion and ambiguities due to different views onto objects is clearly a non-solved research problem so far. In our experiments we also confirm that the obtainable height accuracy is better when all images are used in bundle block adjustment. This was also shown in other research before and is confirmed here. Not surprisingly, the large overlap of 80/80% provides much better object space accuracy – random errors seem to be about 2-3fold smaller compared to the 60/60% overlap. A comparison of different software approaches shows that newly emerged commercial packages, initially intended to work with small frame image blocks, do perform very well.
... Those images are used for instance for visualisation, identification of objects, 3D mapping and automatic building detection or verification (Frommholz et al., 2015, Remondino et al., 2016. A survey amongst users and vendors of airborne oblique camera systems, software developers and researchers was initiated by EuroSDR (Gerke and Remondino, 2014). It revealed that for geometric applications the standard photogrammetric products are still having deficits, especially regarding bundle block adjustment automation and accuracy (Rupnik et al., 2015). ...
During the last decade the use of airborne multi camera systems increased significantly. The development in digital camera technology allows mounting several mid- or small-format cameras efficiently onto one platform and thus enables image capture under different angles. Those oblique images turn out to be interesting for a number of applications since lateral parts of elevated objects, like buildings or trees, are visible. However, occlusion or illumination differences might challenge image processing. From an image orientation point of view those multi-camera systems bring the advantage of a better ray intersection geometry compared to nadir-only image blocks. On the other hand, varying scale, occlusion and atmospheric influences which are difficult to model impose problems to the image matching and bundle adjustment tasks. In order to understand current limitations of image orientation approaches and the influence of different parameters such as image overlap or GCP distribution, a commonly available dataset was released. The originally captured data comprises of a state-of-the-art image block with very high overlap, but in the first stage of the so-called ISPRS/EUROSDR benchmark on multi-platform photogrammetry only a reduced set of images was released. In this paper some first results obtained with this dataset are presented. They refer to different aspects like tie point matching across the viewing directions, influence of the oblique images onto the bundle adjustment, the role of image overlap and GCP distribution. As far as the tie point matching is concerned we observed that matching of overlapping images pointing to the same cardinal direction, or between nadir and oblique views in general is quite successful. Due to the quite different perspective between images of different viewing directions the standard tie point matching, for instance based on interest points does not work well. How to address occlusion and ambiguities due to different views onto objects is clearly a non-solved research problem so far. In our experiments we also confirm that the obtainable height accuracy is better when all images are used in bundle block adjustment. This was also shown in other research before and is confirmed here. Not surprisingly, the large overlap of 80/80% provides much better object space accuracy – random errors seem to be about 2-3fold smaller compared to the 60/60% overlap. A comparison of different software approaches shows that newly emerged commercial packages, initially intended to work with small frame image blocks, do perform very well.
... In order to better understand the current practice and possible needs of users with oblique multicamera systems, in 2014 EuroSDR initiated a survey on the current status of oblique airborne imagery (Gerke and Remondino, 2014). The questionnaire went online in spring 2014 for about 6 months. ...
Oblique airborne photogrammetry is rapidly maturing and entering the workflow of service providers which are tryiong to complement (or replace) the more traditional pipeline based only on vertical images. Many applications embrace the advantages of airborne slanted viewing geometry which comes close to human perception of scenes while standing on the ground. The paper gives an overview on the properties of oblique airborne images, the most common configurations and applications, the processing pipeline, open research issues as well the on going ISPRS / EuroSDR benchmark.
... The applications based on oblique aerial views are multiple: dense point clouds extraction for 3D city modelling (Fritsch and Rothermel, 2013), building detection and reconstruction , urban area classifications (Gerke and Xiao, 2013), building structural damage identification (Nyaruhuma et al., 2012), etc. According to the on-going EuroSDR questionnaire 1 outcomes (Gerke and Remondino, 2014), the two main properties of oblique aerial imagery are the easier object identification and the increase reliability whereas the major applications are visualization, dense image matching, textured 3D city models. Following this interest and potentialities, the main aim of the paper is to review the monoplotting functionality and implement a monoplotting tool for multi-camera aerial systems. ...
... The applications based on oblique aerial views are multiple: dense point clouds extraction for 3D city modelling (Fritsch and Rothermel, 2013), building detection and reconstruction , urban area classifications (Gerke and Xiao, 2013), building structural damage identification (Nyaruhuma et al., 2012), etc. According to the on-going EuroSDR questionnaire 1 outcomes (Gerke and Remondino, 2014), the two main properties of oblique aerial imagery are the easier object identification and the increase reliability whereas the major applications are visualization, dense image matching, textured 3D city models. Following this interest and potentialities, the main aim of the paper is to review the monoplotting functionality and implement a monoplotting tool for multi-camera aerial systems. ...
Aerial photography has a long history of being employed for mapping purposes due to some of its main advantages, including large
area imaging from above and minimization of field work. Since few years multi-camera aerial systems are becoming a practical
sensor technology across a growing geospatial market, as complementary to the traditional vertical views. Multi-camera aerial
systems capture not only the conventional nadir views, but also tilted images at the same time. In this paper, a particular use of such
imagery in the field of building inspection as well as disaster assessment is addressed. The main idea is to inspect a building from
four cardinal directions by using monoplotting functionalities. The developed application allows to measure building height and
distances and to digitize man-made structures, creating 3D surfaces and building models. The realized GUI is capable of identifying a
building from several oblique points of views, as well as calculates the approximate height of buildings, ground distances and basic
vectorization. The geometric accuracy of the results remains a function of several parameters, namely image resolution, quality of
available parameters (DEM, calibration and orientation values), user expertise and measuring capability.
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