From 6ff0094d8c6fb87ff37142a0c4e0b2483d2af486 Mon Sep 17 00:00:00 2001
From: Danny Griffin <dgr@mit.edu>
Date: Tue, 23 Apr 2024 21:53:10 -0400
Subject: [PATCH] writing wip
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topics/02_passive/index.md | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
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{:toc}
# 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_ 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](https://opus4.kobv.de/opus4-btu/files/749/db186714.pdf) in 1867. Since then it has been used for everything from simple measurement or color sampling to recording complex 3D [Motion Fields](https://en.wikipedia.org/wiki/Motion_field)
<img src="images/data_model_photogrammetry.png" alt="Data Model of Photogrammetry">
-<p>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.</p>
+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.
+
+Photogrammetry offers remarkable accessibility and affordability. 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. This accessibility makes photogrammetry an attractive option for various applications, with results that can be sufficiently accurate depending on the specific requirements.
+
+<img src="images/house_scanning.jpg" alt="House">
-<p><img src="images/house_scanning.jpg" alt="House"></p>
+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
@@ -46,7 +51,7 @@ Photogrammetry was first documented by the Prussian architect [Albrecht Meydenba
<p>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.</p>
<p>Real time feedback and processing as models improve. <a href="https://mars.nasa.gov/technology/helicopter/#">Ingenuity Drone</a></p>
-<p><img src="img/lidar_vs_photogrammetry_drone.jpg" alt="Drone imaging"></p>
+<p><img src="images/lidar_vs_photogrammetry_drone.jpg" alt="Drone imaging"></p>
# Key Challenges
Precision is improving but can still be completely thrown off by certain light conditions in much the same way LiDar struggles with smooth surfaces.
--
GitLab