GMT Cartesian coordinate transformations come in three flavors:
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