Image-based 3D survey methods can be considered passive techniques in that they use ambient light and require no additional equipment rather than a camera to gather data. Photogrammetry is the primary image-based method that is used to determine the 2D and 3D geometric properties of the objects that are visible in an image set. In principle, image-based methods involve stereo calibration, feature extraction, feature correspondence analysis, and depth computation based on corresponding points in two overlapping images. It is a simple and low-cost (in terms of equipment) approach, but it involves the challenging task of correctly identifying common points between images. In addition, the location, position, and intrinsic geometric characteristics of the camera and lens are determined to calculate the 3D coordinates of points within a series of overlapping images.
Photogrammetry is usually carried out from an aerial platform and this process is discussed within the aerial survey and remote sensing section of the website. This page explores how photogrammetry is used within a terrestrial setting and across a range of scales. In recent times, the increase in the computation power has allowed the introduction of semi-automated image-based methods such as Structure-from-Motion (SfM). Using SfM software such as Reality Capture and Agisoft Metashape and a series of overlapping images captured with a standard digital camera detailed point clouds, meshes, and associated photo textures can be created extracted to document in high detail cultural heritage objects.