active sensing

.gitignore

@@ -133,3 +133,5 @@ public/
 Gemfile.lock
 
 */*/notes.md
+
+topics/05_processing

index.md

@@ -14,4 +14,4 @@ nav_order: 1
 
 ## [Mechanical Digitizing]({{ '/topics/04_mechanical' | relative_url }})
 
-## [Image processing]({{ '/topics/05_processing' | relative_url }})
+<!-- ## [Image processing]({{ '/topics/05_processing' | relative_url }}) -->

topics/03_active/index.md

@@ -30,8 +30,24 @@ mathjax: true
 
 ## LiDAR
 
+In LiDAR, a laser pulse is sent and bounced back to the sensor. A detected pulse provides a distance measurement in the laser direction. To obtain a full 3D map of the surrounding, the laser needs to rotate to cover a wide variety of angles. The density can be tuned at the expense of a longer capture time.
+
+![](img/lidar.png)
+
+LiDAR has become popular in the car industry, as it is reliable at long range too and is not subject to interference from sunlight. The other main application is architectural scanning, for which the accuracy is far sufficient. In this case, it is often necessary to combine scans from several locations. This creates visible viewing rays in the point cloud distribution.
+
 ## ToF cameras
 
-<!-- Kinect V2 -->
+A time-of-Flight camera is similar to a LiDAR setup with a single emitter and millions of receiver: each is implemented as a CMOS pixel with a demodulator. In this case, we don't use pulses but rather modulate an IR LED with a sine-like profile. This lets the pixels estimate the phase shift of the received sine-wave.
+
+![](img/tof_camera.png)
+
+The phase shift can be measured in several ways, but is typically obtained from 4 amplitude measurements. The strength of the signal is also retrieved, which is important for noise estimation.
+
+![](img/Hughes_TA_3DSensor_PhaseAngleCalculation_moreDetail_slower.gif)
+
+ToF cameras are popular in gaming and realtime applications as they provide a depth map in a single capture, up to 1024x1024 pixels for the Kinect V4 sensor.
+
+One common issue for complex scenes is multipath, where the IR light bounces from a second object before returning to the sensor. This typically produces rounded corners with loss of details. Another issue is flying pixel, occuring on edge regions (mixing of foreground and background signals).
 
-# Light dome
+# Light stage

topics/05_processing/index.md

----
-layout: default
-title: Image processing
-nav_order: 6
-mathjax: true
----
-
-# Image processing
-{: .no_toc}
-
-## Table of contents
-{: .no_toc .text-delta }
-
-1. TOC
-{:toc}
-
-# Filtering
-
-## Convolution
-
-![](img/conv.gif)
-
-## Edge detection
-
-## Fourier transform
-
-# Deep learning
-
-## Classifier
-
-## Segmentation
-
-## Regression