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Scaling (geometry)

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Scaling is a type of linear transformation used in affine geometry. It involves changing the size of an object through a specific multiplier. This multiplier is known as the scale factor. Scaling can enlarge an object or shrink it down. When an object grows, the process is called dilation or enlargement. When an object shrinks, it is called contraction or reduction.

Dilation and contraction
Dilation and contraction

There are two primary ways to categorize scaling based on direction. The first is uniform scaling, also called isotropic scaling. In this method, the scale factor is identical in all directions. Because every dimension changes by the same amount, the resulting shape is similar to the original. A scale factor of one results in congruent shapes, which are identical in size and shape. Common examples include resizing a photograph or building a scale model of an airplane.

Non-uniform scaling, or anisotropic scaling, occurs when scale factors differ across axes. This type of scaling changes the actual shape of the object. For instance, a square might become a rectangle through non-uniform scaling. If the sides are not parallel to the scaling axes, a square could even become a parallelogram. This can happen visually when viewing a billboard from an oblique angle. It also occurs when a shadow falls on a surface that is not parallel to the object.

Mathematics uses specific equations to define these changes. For a simple linear relationship, the equation y = Cx uses C as the scale factor. Here, C serves as the constant of proportionality between y and x. You can calculate a scale factor by dividing the image size by the preimage size. In measurement fields, the scale factor of an instrument is sometimes called its sensitivity. The ratio of any two corresponding lengths in similar figures is also referred to as a scale.

In higher mathematics, scaling is represented using matrices. To scale a 3D object, you multiply each point by a scaling matrix. This matrix uses a vector, such as v = (vx, vy, vz), to define the factors for each axis. Scaling changes dimensions in predictable ways based on these factors. The diameter of an object changes by a factor between the smallest and largest scale factors. The area changes by a factor between the smallest and largest product of two factors. The volume changes by the product of all three scale factors.

Scaling can be applied to any number of dimensions. In n-dimensional space, uniform scaling is achieved through scalar multiplication. This means multiplying every coordinate of every point by the same constant. Non-uniform scaling uses a symmetric matrix. In this context, the eigenvalues of the matrix represent the scale factors. The corresponding eigenvectors represent the axes where those factors apply. If a scaling matrix is diagonal, the axes of scaling are simply the coordinate axes.

Computer graphics often use projective geometry to handle scaling. This involves representing points using homogeneous coordinates. In this system, a point is written as (px, py, pz, 1). Scaling is performed by multiplying this coordinate vector by a projective transformation matrix. This method is essential for rendering complex 3D scenes accurately. It allows for sophisticated transformations that maintain the mathematical integrity of the digital objects.

Scaling also applies to mathematical functions on a graph. If you scale a function vertically, you change its height. A factor greater than one causes dilation, while a factor between zero and one causes contraction. Horizontal scaling changes the width of the function. If the product of the horizontal and vertical scaling factors equals one, the transformation is called a squeeze mapping. These principles allow mathematicians to manipulate and study the properties of complex curves and surfaces.

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File:Sierpinski triangle evolution.svg
Sierpinski triangle evolution.svg
File:Dilation and contraction.svg
Dilation and contraction.svg
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