Pitney Bowes MapInfo Professional - Manual (Page 405)

What is Precision?
The most basic component of any GIS is the spatial data that defines the map features. This spatial data
could not exist without the coordinate systems that are used to specify the location information. Coordinate
precision is a measure of storing spatial data as accurately as possible. Of course, this can be no more
precise than the original data provided. Precision is a measurement of how accurately you can store
and retrieve the spatial data and has nothing to do with the quality of the data. The number of reliable
digits in your coordinate is termed significant digits. Precision is measured in terms of these significant
digits.
• For topics related to precision and map bounds, see Understanding Precision in MapInfo Professional
in the Help System.
Understanding Affine Transformations
An affine transformation allows you to match the points on two vector maps that use different coordinate
systems so they can be used together. The base map stays the same while the derived map is transformed
mathematically to match up coordinates to the base map.
MapInfo Professional provides the definitions for scale, translation, rotation, reflection, and shearing
necessary to support an optional affine transformation for any coordinate system definition. You can
also define a coordinate system with bounds and/or with an affine transformation. This is described in
detail in
Accounting for Affine Transformations and Explicit Bounds in Projection Types .
Description of an Affine Transformation
There are several basic types of transformation that can be applied to the base map using an affine
transformation. These include scaling, translation, rotation, shearing, and reflection.
• For more information, see Understanding Affine Transformations in the Help System.
The scale factor of a transformation indicates the distance between the fixed points of one map versus
the fixed points of the second map. If the only difference between two maps is the scale, the affine
transformation of the derived map is only the same map zoomed in or out around a fixed point. The
orientations of the lines connecting the points, and the angles between these lines, remain the same.
The scaling in the case of the figure below is around the 0,0 point.
The difference between these images is the scale. To create an affine transformation that maps the base
image (A) to the derived image (B), change only the scale.
The translation factor of a transformation is when every point on an image follows a parallel path and
no rotation takes place.
405 MapInfo Professional User Guide
Chapter 15: Working with Coordinate Systems and Projections