Article

Oblique photography and its use

  • Nor Knidud
  • 12 June , 2015

What is oblique photography?

 

In short; oblique means 'under an angle'. The term is mostly used with aerial survey, and what for we are talking about here it is about systematical oblique photography. In general it is being used to capture complete cities, city parts or even larger areas.

 

From the air the area is flown over by an airplane (mostly), following photo runs. Depending on the camera it will record in multiple directions, therefore recording every object in various directions and under various angles. Once finished the result will be that any object in the target area can be displayed in a north, east, south, west direction and, ultimately, even a 3d model is possible. 

 

What is oblique photography used for? 

Especially governmental organisations use this product. It allows them to see as many objects in their area as possible, from many different angles. Think of a tax department in a city that has to estimate vallues of properties. A vertical aerial photo gives a lot of information; but is useless if it is in a low resolution, or if cannot reveal whether it is a garden house or a garage. Take in mind; if the estimate is wrong, the owner will complain, which will cost time and money. Better do it as right as possible.. Next to this also registration purposes and change detection processes make use of it. Or Law and Enforcement departments, infrastructure planning purposes and many other purposes. 

 

How about precision and geometry?

Most oblique photo sets are geo-referenced, so that they can be used in a GIS or CAD environment. This enables compatibility to many other geo-referenced products and is of great benefit for many processes. These processes can be interconnected, which is many circumstances enhances efficiency and saves time & costs. For example oblique imagery can be used together with orthophotos, enablng the user to have a peak under that car parking to check if it is a garage or just some roof. Ofcourse many maps and even 3 models can be connected to the oblique, actually the possibilities are endless. 

 

The precision however, is a different story. Depending on the camera used, many obiques are not comparable with stereophotography. The oblique angle is a complex factor in positioning and referencing the photo. In 99% of the projects, a high accuracy is not yet required, allthough the future will for sure do so. For now, the oblique imagery is mainly seen as visual support tool. However, aerotriangulation is allready possible; but still relatively expensive due to the software needed to perform this.

 

3D and oblique

Oblique can be regarded as the last stop before the  next station: 3D. There are many ways how to build 3D models, but for photorealistic 3D models oblique imagery is simply the best option. Aerotriangulation and stitching procedures for obliques and 3D become smarter and smarter each day.

 

One of these companies is Acute3d (recently acquired by Bently ). Their methodes enable oblique imagery turned into great 3D models. We will go deeper into 3D-oblique-models in one of the upcoming articles. 

 

As for now, oblique is conquering many markets in an upspeed tempo. We will keep you posted on its developments. 

Author

Nor Knidud: Some years of experience in the aerial survey world, and interested in many many aspects that have to with this little big world of photography. The applications that come from aerial survey are endless and technically and commercially very promising.

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