• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0

Algorithmic suggestions for determining when a 'throwing' action occurs

0 posts in this topic


I'm working on a project that involves using the Kinect to play a simple 'basket ball' type game. I've implemented a basic method of determining when the player is 'making a shot', based on relative positions and velocities of their hand. Generally it does work well, however it is rather specific requiring the player to make what I've 'determined' to be the 'correct' throwing action.

So I'm wondering what algorithms or methods might exist that could help me build a more robust, yet at the same time more forgiving means of determining when a player is 'throwing' the ball. I know that sounds counter intuitive. I guess when I say robust/forgiving I mean that it can detect a range of 'throw' attempts, not a narrow definition.

Thinking about it I suppose i'm looking for a weighting or scoring system, that evaluates the player motion giving a value to it each frame and when its above a certain value it is considered a throw. In which case i'm no longer looking for an algorithm but have to re-focus on developing a heuristic to score the motion, which is probably beyond the scope of this post.

There isn't much data to work with, although I have the full skeleton of the player, i'm currently just using the hand position (x,y,z) and from that I can determine the current velocity (compared to previous position) and obtain other useful values such as overall magnitude, angle etc.

I've graphed out the motion of the hand perform a sequence of throws in the graphic attached. This clearly shows very obvious structures to the throwing motion, which i'm hoping would be sufficient for constructing an algorithm around. (graph x-axis is time, y-axis is various units)

Blue line is my current attempt to detect when a throw starts (exceeds a fixed velocity in z axis) and ends (falls below a fixed velocity) The actual values are irrelevant, but 1000 = false (not throwing) 1500 = true (throwing).

The Hand position is then yellow Y axis (height), dark green (at the bottom of graph) Z axis (depth).
The hand velocity is blue for y axis and black for z axis, frequently these match up not only in time, but also in value, suggesting a close to 45 degree angle of throw, though that is non-optimal, should be around 50-65 degrees.
Finally the light green line is the overall magnitude of the velocity in Y and Z axis.

There are issues with my current method, in that since i'm waiting for the z axis velocity of the hand to exceed a specific value, this can mean i'm losing useful data before this point. Indeed it can lead to bogus results when I try to calculate the throwing velocity/force/angle using the data at the start and end points of the throw. This is something i'd like to address, by having an algorithm which can more correctly determine when a throw has started, hence my overall question of this post.

One though I had was to back track from the 'end' point of the throw, when the ball is/should be released from the hand, as this seems to be the simplest point to determine as generally either

a. The difference in y axis between current and last frame should negative. I.e. the players throw has gone through its own apex.
b. The velocity in the z -axis (forward/back from the players body) has dropped to nothing or negative indicating they are no longer moving their hand/arm forward.

Then its a case of looking backwards for some indication of when the throw starts.However again this is very specific and looking at the graph, there are very clear patterns in the throwing motion that I can't help feeling could be utilised with some algorithm to provide a more robust method of detecting the start/end points of a throw. Perhaps something like pattern matching?

So I'd be interested to hear of any suggestions of algorithms or methods to explore.


Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  
Followers 0