Solved

geometry tranform problem

Posted on 2004-09-16
4
203 Views
Last Modified: 2010-04-07
Hi,

My linear algreba's a little shaky, hence the question...

I have a non axis aligned box parameterised something like:

vector3 center
vector3 extents
vector3 eulers

To draw this thing I apply transformations like this:

extents -> eulers -> center
ie. scale -> rotate -> translate

I want to recalculate the translate when I update the scale to give the same tranformation such that a particular side of the box remains in the same position.

The box is editable by the user who can pull the edges to scale the box, or use a widget to rotate the box. With zero rotations the box behaves ok, I calculate the center to compensate for the adjusted edge. However when the box is rotated this calculation is not so simple I cannot get the same behaivour, the box moves around.

The end result needs to be a 4x4 matrix that represents the tranformation so there maybe another representation would be better.

Any help really appreciated.

faraz
0
Comment
Question by:_faraz
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
4 Comments
 
LVL 2

Expert Comment

by:cmreichl
ID: 12084358
The reason for this behavior is that the rotation equations your using are doing calculations about the origin...   Therefore if your object is not at the origin the whole object is then rotated as if the origin was its center.  An easy fix would be to remember its center, convert the numbers to the origin, and then convert back once rotation is calculated.  (Since your just calculating numbers and not actually moving the object, this isn't an inefficient method).

-Chris
0
 

Author Comment

by:_faraz
ID: 12084606
This was my original 'solution', however it doesn't really give the expected (from the user's point of view) result. The user expects the rotation to occur about the current center of the box, not the original center. As the box is scaled the center obviously shifts, the rotation occurs around the correct center before the translation is applied, but this invalidates the translation.

I think the problem is actually more to do with keeping the opposite edge to the one thats begin moved stationary.

It may be simpler to work by transforming faces/vertices (user experience is the same) then calculate the matrix from the vertices when I need it, maybe with the coord frame defined by the planes since this bit is not performance critical. That way I'm not dealing with a representation based on transformations, I just apply a transformation to vertices as I need it.

hmm...I'll give this ago, thanks for your help (got me thinking about this in a different way!)

faraz
0
 
LVL 1

Accepted Solution

by:
Computer101 earned 0 total points
ID: 12388724
PAQed, with points refunded (250)

Computer101
E-E Admin
0

Featured Post

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Recently, in one of the tech-blogs I usually read, I saw a post about the best-selling video games through history. The first place in the list is for the classic, extremely addictive Tetris. Well, a long time ago, in a galaxy far far away, I was…
Performance in games development is paramount: every microsecond counts to be able to do everything in less than 33ms (aiming at 16ms). C# foreach statement is one of the worst performance killers, and here I explain why.
This video Micro Tutorial shows how to password-protect PDF files with free software. Many software products can do this, such as Adobe Acrobat (but not Adobe Reader), Nuance PaperPort, and Nuance Power PDF, but they are not free products. This vide…
In this video, viewers are given an introduction to using the Windows 10 Snipping Tool, how to quickly locate it when it's needed and also how make it always available with a single click of a mouse button, by pinning it to the Desktop Task Bar. Int…

729 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question