Change Of Coordinate Transformations
Change of Coordinate Transformations |
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Change of Coordinate Transformations
- An example of various coordinate transformations applied to simple geometry.
Contents
Basic Description
A Change Of Coordinate Transformation is a transformation that converts coordinates from one coordinate system to another coordinate system. Transformations such as scaling, rotating, and translating are usually looked upon as changing or manipulating the geometry itself. However, with change of coordinate transformations, it is important to realize that the coordinate representation of the geometry is modified, rather than the geometry itself.
The Change of Coordinate Systems in general is also common for converting coordinates from system to another, such as from Cartesian coordinates to Cylindrical coordinates.
A More Mathematical Explanation
- Note: understanding of this explanation requires: *Linear Algebra
Change of coordinate transformations are different for vectors and points.
Vectors
[...]Change of coordinate transformations are different for vectors and points.
Vectors
- Consider a coordinate system A, and a vector . The coordinates of relative to coordinate system A is . It is also apparent that
- In which and are unit vectors along the x and y-axes of coordinate system A. Now consider a second coordinate system, B. In coordinate system B,
- More generally, given along with and , may be found using the formula above.
- In 3-dimensional space, given then
- In which , , and are unit vectors along the x, y, and z-axes of coordinate system A.
- Given:
- , , , and
- Then:
- Explanation:
- The formula, , was used for the change of coordinate transformation. The dot product of 5 and is 5, and the dot product of 7 and is 7. Since a zero vector, the dot product of 13 and is 0.
- Given:
Points
- Consider a coordinate system A, and a point . Point may be expressed as:
- In which and are unit vectors along the x and y-axes of coordinate system A, and is the origin of coordinate system A. Now consider a second coordinate system, B. In coordinate system B,
- More generally, given along with , , and relative to coordinate system B, then may be found using the above formula.
- In 3-dimensional space, given then
- In which , , and are unit vectors along the x, y, and z-axes of coordinate system A, and is the origin of coordinate system A.
- Given:
- , , , , and
- Then:
- Explanation:
- The formula, , was used for the change of coordinate transformation. The dot product of 6 and is 6, the dot product of 4 and is 4, and the dot product of 21 and is 21. , or 17, is then added to the resulting vector.
- Given:
Matrix Representation
- The change of coordinate transformation varies for points and vectors and thus results in two different equations. However, by using homogeneous coordinates, both cases may be handled with the following equation:
- When , the equation handles the change of coordinate transformation for points; when , the equation handles the transformation for vectors. As long as the -coordinate is set correctly, there is no need to keep track of two different equations. Thus the change of coordinate matrix may be defined as:
- Click here for an overview of matrix multiplication.
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Additional Resources
References
Luna, Frank D. Introduction to 3D game programming with DirectX 10. Plano, Tex: Wordware Pub., Inc., 2008. Print.
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