Get Into Photogrammetry.

 # How to use photogrammetry to create 3D models from photos

Photogrammetry is a technique that allows you to create realistic 3D models from a series of overlapping photos of an object, structure, or scene. In this blog post, I will explain what photogrammetry is, how it works, and what you need to get started.

## What is photogrammetry?

Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant imagery and other phenomena. [1]

Photogrammetry can be used for various applications, such as mapping, surveying, engineering, archaeology, cultural heritage, gaming, film making, and more. Photogrammetry can also be used as a low-cost and accessible 3D scanning method that can capture both small objects and large landscapes.

## How does photogrammetry work?

Photogrammetry works by using 3D geometry to reconstruct the shape and position of an object from multiple images taken from different viewpoints. The basic principle is that if you know the camera position and orientation for each image, you can triangulate the 3D coordinates of any point that is visible in at least two images. [2]

To do this, you need to perform the following steps:

- Capture: You need to take a series of photos of your subject from different angles and distances, making sure that there is enough overlap between them (at least 60% for aerial photos and 80% for terrestrial photos). You also need to ensure that the lighting is consistent, the focus is sharp, and the camera settings are fixed. You can use any camera, from a smartphone to a DSLR, as long as it has a good resolution and quality. You can also use a tripod or a drone to stabilize your camera and cover more area.

- Process: You need to upload your photos to a photogrammetry software, which will automatically align them and extract common features (called keypoints) from each image. The software will then match these keypoints across images and use them to estimate the camera parameters (position, orientation, focal length, etc.) for each image. This process is called bundle adjustment. The software will then use these parameters to generate a sparse point cloud, which is a set of 3D points that represent the shape of your subject. The software will then refine this point cloud by adding more points from the images and removing outliers. This process is called dense reconstruction. The software will then project the colors from the images onto the point cloud to create a textured mesh, which is a surface model that consists of polygons (usually triangles) with color information. The software will also generate an orthomosaic map, which is a georeferenced image that combines all the photos into one seamless image with no distortion or perspective.

- Edit: You can use the photogrammetry software or another 3D modeling software to edit your 3D model. You can crop, scale, rotate, smooth, simplify, or enhance your model as you wish. You can also apply filters, adjust colors, add details, or remove unwanted elements. You can also export your model in various formats (such as OBJ, STL, PLY, etc.) for further use or sharing.