🌍1.6 Useful Concept

This section introduces you to some of the basic photogrammetric knowledge required to use Get3D Mapper, as well as the relevant terminology in the software.

Oblique Photogrammetry

Inclined photogrammetry is the simultaneous acquisition of surface images from multiple different viewpoints by flying a platform with a camera on board to obtain rich surface information for the production of mapping and geographic information products.

Unmanned Aerial Vehicle (UAV)

It is an unmanned aircraft that can be equipped with different sensors and is operated by radio remote control equipment and its own program control device. The images captured by the UAV can be imported into the software for modeling.

Close to Ground Photography

Obtain high-resolution lateral texture and structural details of features using mobile phones, digital cameras, handheld gimbals, vehicle-mounted mobile surveys, stationary laser scanning, or low-altitude ring photography.

Pose File

A comprehensive representation of position (Position) and orientation (Orientation) in space, the Pose file is used to record information about the camera's position and pose when a photo is taken, recording the coordinates (x, y, z) of the position in three-dimensional space and the quaternion or rotation matrix of the camera's pose.

Exif (Exchangeable Image File Format)

EXIF is a metadata standard embedded in image files and is primarily used to store information about the image taken. This information includes shooting time, exposure settings, white balance, camera model, focal length, geographic coordinates, and so on.

Photo Control Point

image control points are control points that are laid and measured in the field directly for the control point encryption of photogrammetry or mapping needs. Image control points include image plane control points with plane coordinates only, image elevation control points with elevation only, and image level and elevation control points with both plane coordinates and elevation.

Ground Sampling Distance(GSD)

Ground resolution, which represents the actual size of the ground (usually measured in metres) represented by one pixel (Pixel), and is related to the pixel size of the image and the height of the camera at the time of imaging, etc. GSD = (P×H)/F P represents the pixel size (in metres per pixel), H represents the camera height (in metres), and F represents the focal length of the camera (in millimetres).

Tile

3D model results are generally stored in a certain grid size, with individual grids called tiles. When large-scale 3D scene, processing the whole scene or terrain as a whole may lead to the problem of large amount of individual model data and low processing efficiency. Each tile represents a localised area that can be independently reconstructed in 3D. This chunking approach can significantly reduce the amount of data for a single processing task and can support distributed computing of tasks to improve processing speed. Tile technology also makes data transmission, storage and display more efficient.

Relative Orientation

Relative orientation refers to the work of restoring or determining the relative relationship between pairs of images at the time of photography, i.e., the work of solving the relative orientation elements of stereoscopic pairs. It is to determine the internal and external parameters of the camera by observing the positional relationship of the objects in the image in different viewpoints. The relative orientation of stereo image pairs is to restore the interrelationship of the two neighbouring image beams at the time of photography, so as to make the pairs of light rays of the same name intersect each other.

Absolute Orientation

Absolute orientation is the linking of an image to a ground coordinate system through measurements with ground control points. With the help of known ground control points, it translates, rotates, and scales the three-dimensional geometrical model, which has been relatively orientated, to incorporate it into the ground photogrammetric coordinate system. In this way, we can obtain the true position of objects on the ground.

Camera internal orientation

The internal orientation (or internal parameters) of a camera refers to a number of internal properties of the camera: the sensor size of the camera, the focal length of the lens, the position of the principal points in the image plane, and the lens distortion. We call a group of images a set of images with identical internal orientations. For a physical camera with all settings fixed, the internal orientation is unique. Even for two cameras of the same model with the same settings, their respective images do not constitute a single image group.

Tie Point

Model Connection Points are used for neighbouring models to connect image points with the same name.