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dx / d(phi), dx / d(lambda);
dy / d(phi), dy / d(labmda).

dx / d(phi), dx / d(lambda);
dy / d(phi), dy / d(lambda).

A nice addition to the elliptical portrayal of the TI is to show the major and minor semiaxes, too: then, at a glance, you can assess the grid convergence. I also show a standard circle (representing no distortion) concentric with each TI because it improves the reader's ability to gauge the amount of distortion represented by each ellipse.

A nice addition to the elliptical portrayal of the TI is to show the directions of the local meridian and parallel: then, at a glance, you can assess the grid convergence. I also show a standard circle (representing no distortion) concentric with each TI because it improves the reader's ability to gauge the amount of distortion represented by each ellipse.