We carry out a study with the collection of aerial images to obtain a small 3D model and a cloud of points.

What is photogrammetry?

On some occasions we have defined photogrammetry as measuring on photographs. And it is that photogrammetry is a technique whose objective is the study and the precise definition of the shape, dimensions and/or position in space of an object, through the data obtained from one or several photographs.

One of the main applications of photogrammetry is surveying since it allows measuring coordinates in three dimensions and also results in the complex representation of an object in an easy-to-use document. To this is added the instantaneous nature of the record, with the consequent agility to process the information compared to the classic topography.

Advantages

There are many advantages of photogrammetry over classic topography. How is the agility and speed in data collection. It is also possible to access terrain that is difficult to access and more so today, in which the use of drones in photogrammetry allows reaching all kinds of places.

In addition, the weather conditions do not influence it. In the photographs obtained, all the details of the terrain are recorded continuously, while in the classical topography only points measured in the coordinates are obtained.

There are two types of photogrammetry, terrestrial and aerial:

• In terrestrial photogrammetry there is a fixed point of view and therefore its coordinates and focus orientation are known.
• Regarding aerial photogrammetry, the point of view is mobile and provides a wide range of capture, but the position of the camera or its orientation at the moment of shooting are not known, although technology and digitalization of processes can solve these problems.

 Methodology

The method used to obtain these images is as follows:

• Object photography. To do this, you must first plan the flight (if you are going to opt for aerial photogrammetry) and take pictures so that everything is well programmed and in the necessary conditions. In addition, the survey of ground control points should also be planned using ground photogrammetry.
• Image processing. Once the photographs are obtained, they must be processed.
• Orientation of the images. The frames must be placed in the proper position with their trust marks and in the same position as the photographic capture order. To reconstruct and form the model, two systems can be chosen: by restitution or by rectification. When doing it by restitution, the turns, translations and scales are applied. In this way, a coordinate model of the terrain is obtained and the scaling of the object is included to work with real measurements. In the case of doing it by rectification, after the orientation of the light beam (interior and exterior) the intersection between that light and the digital terrain model (DTM) of the space to be determined is achieved.

The applications of photogrammetry are multiple. It can not only be applied in topography, digital cartography, orthophotography, environment and agriculture. It also offers great advantages for other sectors such as archeology and heritage conservation, architecture. In recent times it is also being used a lot in video games or movies, since it is a method that offers great realism.