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5.1 Cartesian transformations

GMT Cartesian coordinate transformations come in three flavors:

- Linear coordinate transformation
- Log coordinate transformation
- Power (exponential) coordinate transformation

These transformations convert input coordinates to locations on a plot. There is no coupling between and (i.e., and ); it is a one-dimensional projection. Hence, we may use separate transformations for the - and -axes (and -axes for 3-D plots). Below, we will use the expression , where is either or (or for 3-D plots). The coefficients in depend on the desired plot size (or scale), the chosen domain, and the nature of itself.

Two subsets of linear will be discussed separately; these are a polar (cylindrical) projection and a linear projection applied to geographic coordinates (with a 360° periodicity in the -coordinate). We will show examples of all of these projections using dummy data sets created with gmtmath, a ``Reverse Polish Notation'' (RPN) calculator that operates on or creates table data:

    gmtmath -T0/100/1  T SQRT = sqrt.d
    gmtmath -T0/100/10 T SQRT = sqrt.d10

Subsections

- 5.1.1 Cartesian linear transformation (-Jx -JX)
  - 5.1.1.1 Regular floating point coordinates
  - 5.1.1.2 Geographic coordinates
  - 5.1.1.3 Calendar time coordinates
- 5.1.2 Cartesian logarithmic projection
- 5.1.3 Cartesian power projection

Next: 5.1.1 Cartesian linear transformation Up: 5. GMT Coordinate Transformations Previous: 5. GMT Coordinate Transformations Contents Index