NCL Graphics: Axes

axes_1.ncl: This is a simple script that uses dummy data with a Y axis that has irregularly-spaced values. The second frame shows how setting gsnYAxisIrregular2Linear to True will linearize the Y axis. Note what this does to the contours.

axes_2.ncl: This script shows how to convert an irregular axis to a log axis by setting gsnYAxisIrregular2Log to True.

axes_3.ncl: This script shows various ways you can control all four axes of a plot. Although this is an XY plot, these techniques apply for contour and vector plots as well.

axes_4.ncl: This script shows how to replace the default axes with a cartesian coordinate system.

If you want to be sure that point (0,0) is the center of the cartesian axes, then you can either modify the "attach_vert_axis" and "attach_horiz_axis" functions in this script, or do it the "lazy" way by setting:

res@trXMinF = -(max(x))
res@trXMaxF = (max(x))
res@trYMinF = -(max(y))
res@trYMaxF = (max(y))

Where "x" and "y" represent the range of your X and Y axes.

axes_5.ncl: This script shows how to convert a linear axis to a logarithmic axis in a contour plot, by setting gsnYAxisIrregular2Log to True.

Note that the original Y axis looks linear, but is considered "irregular" because it has a coordinate array. Hence, the gsnYAxisIrregular2Log will work.

axes_6.ncl: This script shows how to increase the range of the X and Y axes of a contour plot that has coordinate values set.

If you try to set any of trXMinF, trXMaxF, trYMinF, and/or trYMaxF to a value outside the range of the data's coordinate values, then you will get an error:

warning:ContourPlotSetValues: current transformation requires trXMinF
     to be within data coordinate range: resetting

In this example, the original latitude coordinate array goes from -87.86 to 87.86, and the level array from 200 to 1000. We show how to use the new function to increase the latitude array by two elements, -90 and 90, and the level array by one element, 150 mb. The data array is also increased by 2 elements in the lat dimension, and 1 element in the level dimension.

axes_7.ncl: This script creates a plot of dummy data that has both irregular X and Y coordinate arrays. It then linearizes the X axis by setting gsnXAxisIrregular2Linear to True.

Note the change in the plot along the horizontal direction.