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Using Calibration to Translate Video Data to the Real World

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This article was originally published at NVIDIA's website. It is reprinted here with the permission of NVIDIA.

DeepStream SDK 3.0 is about seeing beyond pixels. DeepStream exists to make it easier for you to go from raw video data to metadata that can be analyzed for actionable insights. Calibration is a key step in this process, in which the location of objects present in a video stream is translated into real-world geo-coordinates. This post walks through the details of calibration using DeepStream SDK 3.0.

Design

The DeepStream SDK is often used to develop large-scale systems such as intelligent traffic monitoring and smart buildings. This approach to calibration is meant for complex, scalable environments like these, and does not require a physical presence at the site.

Background

One of the big issues with extracting usable data from video streams is taking an object detected by the camera and translating it into a geo-location. Take a traffic camera as an example. When the camera sees a car, the raw image of the car isn’t useful to a smart cities system on its own. The car would ideally be placed in an information grid that also projects a live bird’s eye view of the activities in the city for the operator’s use.

Doing this means translating that camera image into latitude and longitude coordinates corresponding to the car’s location on that intersection. Technically, this is a transformation from the image plane of the camera (image of the car) to a global geo-location (latitude/longitude coordinate). Transformations like this are critical to a variety of use cases beyond simple visualization. Solutions that require multi-camera object tracking, movement summarization, geo-fencing, and other geo-locating for business intelligence and safety can leverage the same technique. We call this calibration.

Let’s take a closer look at how to approach calibration for applications built using DeepStream 3.0.

Approaches to Calibration

Multiple approaches exist for calibrating cameras to yield global coordinates. Several popular methods use a process based on inferring the intrinsic and extrinsic camera parameters. Global coordinates are then inferred with a simple geometric transformation from camera world to the real world.

One way to do this is to use a “checkerboard” pattern to infer the camera parameters. From there, a homomorphic transformation (translation from image plane to real-world) can be used to infer global coordinates.

While the checkerboard approach is a high-fidelity method for calibration, it’s both labor and resource...