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Passive scanning

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Photogrammetry

Photogrammetry is the collection and organization of 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.

Photogrammetry was first documented by the Prussian architect Albrecht Meydenbauer in 1867. Since then it has been used for everything from simple measurement or color sampling to recording complex 3D Motion Fields

Unlike other scanning methods that require precise orbital plans or specialized equipment, photogrammetry can be achieved simply by flying a drone in a circular pattern and capturing multiple photos. Utilizing the location data from the drone, one can construct detailed models like the example shown here: A typical medium resolution aerial photogrammetry scan of a barn. With 50-100 images a reasonably accurate model can be produced. Such models are often used in surveying and restoration projects from the scale of hand helf objects to cities. This accessibility makes photogrammetry an attractive option for various applications, with results that can be sufficiently accurate depending on the specific requirements.

However, it's essential to note that photogrammetry lacks inherent scale. Without a reference point or prior knowledge of the camera locations, the resulting model lacks a definitive scale, as cameras inherently lack absolute scale information. Therefore, incorporating at least one reference point is crucial. For example, marking a facade with visual markers or known distances, such as pieces of tape, allows for scaling within a 3D modeling program based on these references.

Stereo Matching

Stereo matching is also known as "disparity estimation", referring to the process of identifying which pixels in multiscopic views correspond to the same 3D point in a scene.

Early uses in stereophotogrammetry, the estimation of 3d coordinates from measurements taken from two or more images through the identification of common points. This technology was used throughout the early 20th century for generating topographic maps.

While the analog versions of these techniques have waned in popularity, stereophotogrammetry still has applications for capturing dynamic characteristics of previously difficult to measure systems like running wind turbines.

When is it useful? Photogrammetry is useful for outdoors settings, where all you need is a handheld camera and some patience. In this example, note the loss of quality towards the top, as pixel resolution becomes problematic:

Arc de Triomphe - photogrammetry by Nicolas Diolez on Sketchfab

Key Benefits

1. Unified Workflow Geometry and texture/color in one workflow.
2. Affordability and flexibility. Depending on the end use application almost any camera will work given there is enough light and your post processing software is robust.
3. Real Time Feedback & Processing* *as models improve. Ingenuity Drone relies on photogrammetry-based onboard processing for ground distance estimation, showcasing the efficacy of passive sensing approaches in complex environments.

Key Challenges

1. Lighting Light conditions in the scene are crucial to the quality of the scan. A controlled environment is highly preferred. Precision is improving but can still be completely thrown off by certain light conditions in much the same way LiDar struggles with smooth surfaces.

2. Precision Limitations Increasingly industry pairs vision systems for photogrammetry with laser systems to balance the benefits of both.

Software

Open Source

AliceVision Open-source photogrammetric computer-vision framework
Meshroom is the 3D Reconstruction Software built on AliceVision

3D Software Suites

Autodesk ReCap
Agisoft Metashape Pix4D - Uses ML for improving accuracy while scraping information on the contents of photogrammetry data sets.

Apps

iPhone and Android apps for photogrammetry and now LiDAR scanning have multiplied over the last several years:

Polycam
Rekrei
Adobe Aero
ScandyPro
Bellus

Scan the World
Quixel Megascans

Camera Properties

Creality Ferret Pro Iphone 13

Intrinsics and extrinsics parameters

Levenberg–Marquardt algorithm or damped least-squares algorithm (dls) are used to minimize the error across 3d coordinates. This procedure is typically called bundle adjustment.

Groundwork camera properties and standards for USGS photgrammetry surveys.