Degrees of freedom: what they are and what the D-POINT 6 DoF digital pen is

Degrees of freedom: what they are and what the D-POINT 6 DoF digital pen is

I degrees of freedom (DoF, Degrees-of-Freedom) in the electronics field are a crucial concept for understanding the movement and orientation capabilities of a device in a three-dimensional space. Sensors e tracking systems they allow you to interact with the surrounding environment and monitor the movement of the device itself.

The accelerometri, for example, allow you to determine the linear movements of the device on the three axes x, y, z; the position sensors they provide information about direction and position relative to a reference point. THE gyroscope measure the angular velocity around the three axes while i magnetometri they measure the magnetic field and are often used to determine the direction relative to the Earth’s magnetic field.

In game controllers, drones, virtual reality (VR) and augmented reality (AR) devices, the ability to monitor movements and orientation is key to ensuring an immersive and interactive user experience. In the case of input devices Like digital pens, degrees of freedom allow the user’s movements to be precisely tracked, making it easier to interact with the system.

What it is and how it works D-POINT, the 6 degrees of freedom (DoF) digital pen

An interesting project has just popped up on GitHub open source digital pen. Named D-POINT, it uses the coupling optical-inertial tracking ensuring 6 degrees of freedom input with low latency, pressure sensitivity and sub-millimeter precision. The pen can be used on any flat surface and works with webcam consumer grade.

The main body of the pen was 3D printed and is made up of two halves, which can be combined with each other. The pen contains a force sensor, a lithium battery that charges via USB-C, and a development board based on Arduino for logic and Bluetooth.

D-POINT 6 degrees of freedom digital pen

The digital pen prototype uses 8 ArUco markers. These are visual signals also used in applications computer vision for estimating the position and orientation of objects or devices within three-dimensional space. They are particularly used in camera-based tracking and recognition systems.

I six degrees of freedom describe the possible movements that the pen can make along the three different directions or axes: along the x axis (forward and backward), along the y axis (left and right), along the z axis (up and down), rotation around the x-axis, the y-axis and the z-axis.

Visual Pose Estimation (VPE)

The visual estimation of the poseo Visual Pose Estimation (VPE), is a process that uses visual information, often acquired from a camera or vision system, to estimate the position and orientation of an object relative to a reference coordinate system. The technique is widely used in computer vision, robotics, augmented reality and other fields where it is necessary to know the position and orientation of objects or devices within three-dimensional space.

6 DoF digital pen structure

A camera or vision system captures an image of the scene where the object of interest is located. This image may contain visual features, such as landmarks or markers, that can be used to establish the location and orientation of the object. The ArUco markers, mentioned above, are used just like known reference points.

Pose estimation algorithms calculate the position and theorientation of the object with respect to the camera or vision system.

D-POINT is based on a four-step approach: First use OpenCV, a cross-platform software library for computer vision, in order to detect the angles of each ArUco marker visible on the pen. We then move on to exploit a simple 2D motion model to estimate and correct the effects of rolling shutter on the observed positions.

The PnP algorithm, short for “Perspective-n-Point,” is then used to estimate the position and orientation of the object in 3D space relative to the camera. Given a set of known 3D points and their corresponding 2D projections on the camera, the PnP algorithm estimates the object’s pose relative to the camera.

Finally, using the information collected, D-POINT calculates the position and orientation of the pen tip with respect to the drawing surface.

Design files and source code available for those who want to build the smart digital pen

The author of the D-POINT project explains that the device was created for the purposes of discussing a degree thesis. At the moment, therefore, there is nothing “plug and play“: anyone interested can still use the design files and source code published on GitHub to create the 6 DoF pen themselves and improve it further.

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