How Calibration Matters for Artificial Intelligence and Machine Learning
By: Adam Rodnitzky
Tags: Autonomous Cars, Robotics, Machine Learning, Artificial Intelligence, Computer Vision

The Evolution of Image-Based Inputs for Machine Learning

In the beginning, there were pictures. Simple, static pictures of all sorts of scenes and objects: Dogs. Cars. Houses. People. Fed into systems like Deep Dream, they trained classifiers which then generated their own hallucinated outputs from those inputs. Some of the results were predictably hilarious. But some were also incredibly realistic, and hard to discern from the real-world inputs from which they were derived.

Photo: Public Domain / via Wikipedia

Next, came pre-recorded video. In this phase of image-based machine learning (hereafter referred to as “ML”), these video streams were often used to train systems to separate objects from environments, or to discern different environmental states based on multiple observed factors. These formed some of the first data sets to be used to train machine learning systems used for autonomous vehicles (aka, an “AV”). But, and this is important to note, they were not used in real-time during an AV’s operation.

Now, however, the applications that rely on imagery-trained ML systems have significantly leveled up. These new applications are low-latency and they are real-time. They span a range of industries and use cases, from self driving cars to supply chain robots.

Real-Time Image-Based Machine Learning Relies on Reliable Sensing Inputs

The real-time nature of these applications presents a critical challenge that must be properly managed by the sensor systems that feed them: the data that they receive must be accurate, as it is processed and analyzed in real-time to determine the immediate and subsequent actions of the application.

Sensors, as we know, can fail in multiple ways during deployment:

Intermittent communication faults (for instance, a flaky USB connection)

External impediments (for instance, road dust occluding a camera lens)

Unnoticed or inconsistent shifts in sensor calibration (for instance, a sensor with an insecure mounting)

Improperly configured sensors (for instance, a camera that does not operate properly in typical daylight settings)

Worse yet, sensors often fail silently. They still emit a data stream, and the ML system assumes that that means the sensors are functioning 100% properly. However, if any of the above scenarios are occurring, they will be sending anomalous data into the ML system. This can create corrupted data sets that lead to immediate errors, or compounding errors that increase over time.

The Impact of Silent Sensor Failures on ML Systems: An Example

Consider the below scenario:

The System: A new autonomous taxi designed to operate in urban settings

A new autonomous taxi designed to operate in urban settings The Task: Recognize when the autonomous taxi is too close to a curb while in motion

Recognize when the autonomous taxi is too close to a curb while in motion A Key Parameter: Distances under 1.2 m present an unsafe condition due to the presence of bike lanes and cyclists in urban settings

Distances under 1.2 m present an unsafe condition due to the presence of bike lanes and cyclists in urban settings The Inputs: GPS data; wheel encoders to measure distance traveled; LiDAR sensors and HDR CMOS sensors to capture scene geometry

GPS data; wheel encoders to measure distance traveled; LiDAR sensors and HDR CMOS sensors to capture scene geometry The Problem: Silent LiDAR sensor calibration fault due to a loosened sensor mount; extrinsic calibration shifts by 3 cm in two axes when AV is in forward motion; returns to near-calibrated state at rest. AV driven during rain results in water occlusion on CMOS sensors.

Silent LiDAR sensor calibration fault due to a loosened sensor mount; extrinsic calibration shifts by 3 cm in two axes when AV is in forward motion; returns to near-calibrated state at rest. AV driven during rain results in water occlusion on CMOS sensors. The Result: Undetected anomalous data that becomes part of the training set causes the AV to operate within 0.7 m of the curb, which is 0.5 m too close.

Ensuring Reliable, Accurate Sensor Inputs for ML

Some of the current thinking around sensor failures in machine learning systems suggests that the errors themselves are a valid input for training. This is true, to a degree. The challenge, however, is that the system needs to be able to recognize that a sensor is failing and properly classify that input as such. This is easier to do under controlled circumstances. In the real world, relying on these processes can become a riskier proposition.

Therefore, the best practice remains ensuring that sensors operate accurately and reliably as much as possible. Achieving this requires effort. It involves:

Capturing and analyzing statistically significant subsets of sensor logs to identify and properly classify common failure states

Visually assessing sensors for external impediments after sessions when failures are detected

Confirming sensor calibration and recalibrating sensors frequently

Testing sensors with multiple configurations, and then capturing and analyzing sensor logs to identify operational deficiencies before determining the optimal configuration

This is not an insignificant amount of work. It requires data analysis, sensor expertise, calibration expertise and copious amounts of engineering time. But, as is the case with any data-driven system, it’s a matter of garbage in, garbage out. The investment in proper sensor operation pays off when data sets deliver the expected outcomes, and the ML-powered agent can operate successfully in the real world.

Of course, we can help ease this burden. Tangram Vision automates sensor management, ensuring that otherwise silent failures are detected and handled efficiently, and uptime with optimal performance is maximized.