Lawrie Griffiths

Lawrie Griffiths has written 38 posts for leJOS News

Publishing data to MQTT

The MQTT message broker is very popular for publishing sensor data for Internet of Things (IoT) devices. This post shows you how to publish EV3 sensor data to it. The image above shows a flow that subscribes to the sensor data topic and prints it out using the very popular node-red visual web tool. To … Continue reading

openCV web streaming

This post is a start of a series on using openCV with leJOS robots controlled from Android phones. openCV is supported in the latest snapshot of leJOS and will be supported in the next release, which is coming soon. I will start off with a version of my Webcam HTTP streaming code. This uses openCV … Continue reading

Webcam HTTP streaming

To follow up my post on webcam streaming, here is an example of HTTP MJPG streaming. This allows you to open the stream in a browser using a URL like However, Chrome does not let you open this directly – it must be embedded in an HTML document, e.g.: Here is the EV3 code, … Continue reading

leJOS Navigation: Navigation model

This is the seventh in a series of posts on leJOS Navigation. This post is about the Navigation model. The navigation model is a way to integrate all the leJOS navigation features, and communicate with an application on the PC. The PC application typically shows your robot moving around in a mapped area, and lets … Continue reading

leJOS Navigation: Path finding

This is the sixth of a series of posts on leJOS Navigation. It describes how to do path finding. leJOS has a variety of path finders that all implement the PathFinder interface. The two most useful are ShortestPathFinder and NodePathFinder. Both of theses implementations require a line map of the environment. How to create this … Continue reading

leJOS Navigation: Mapping

This is the fifth in a series of posts on leJOS navigation. The first covered moving robot around using pilots, the second covered localization and pose providers, the third covered object detection and the fourth waypoint navigation. This post covers how to produce a static map the environment you are using for navigation. Such maps … Continue reading

leJOS Navigation: Waypoint Navigator

This is the fourth in a series of posts about leJOS navigation. The first dealt with moving the robot around using pilots, the second with finding out the robot’s location and heading using pose providers, and the third with detecting obstacles and other objects. This post deals with navigating using co-ordinates including following a series … Continue reading

leJOS Navigation: Object Detection

This is the third of a series of posts on leJOS navigation. It covers object detection. We first looked at pilots that move your robot around. We then found that you could easily add localization to your navigation application and keep track of the robot’s position and heading. Another thing that you are likely to … Continue reading

leJOS Navigation: Pose Providers

This is the second of a series of posts on leJOS navigation. The first dealt with pilots, which move mobile robots around. This post deals with pose providers which implement localization, i.e. they tell you where your robot is. The robot’s pose is its position and heading in space. In two-dimensional navigation, this is typically … Continue reading

leJOS Navigation: Pilots

This is the first of a series of posts on leJOS Navigation features. This post concentrates on how to move a mobile robot around. leJOS provides features for two-dimensional navigation, i.e. moving a robot around on a surface such as a the floor in your house or the ground outside. The leJOS navigation classes would … Continue reading

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