It is remarkable that I've struggled to find any examples in the Octave documentation or other people's tutorials or examples on how to plot an image (or matrix) with axis coordinates that aren't the pixel or cell numbers.
% These are our eventual axis coordinates.
x = linspace(-10,10,100);
y = x - 2;
% Generate an Airy disk
rad = sqrt( xg.^2 + yg.^2);
airy = besselj(1,rad)./rad;
airyintensity = abs(airy).^2;
% The normal imagesc invocation. Note axis ratio.
% Now invoke with axis vectors before the image/matrix
% Demonstrate the coordinates a little more clearly
% Coordinate axes are taken to be the center of the
% image pixel.
% What about non-linear axes. Not handled correctly like this.
% This case is dealt with another time,