MATLAB Label points along a curve with nice offset

Using MATLAB's text to label points along a parametric curve often results in the label blocking the curve. This can be avoided for simple curves by using the text alignment properties or by offsetting the points. However, these techniques do not work for curves that change direction.

This tool, ptlabel_along, interpolates the provided curve to place points at just the desired parameter values. It also computes the local slope of the line and uses that to offset the text perpendicular to the line. This makes labeling parameter values along curves easy and beautiful.

Example Use

th = linspace( 0, 360, 181 );
thmark = 0:15:359;
x = cos( th * pi / 180 );
y = sin( th * pi / 180 );
plot( x, y );
axis equal
axis off

ptlabel_along( x, y, th, thmark );

Documentation

[HL, HT] = PTLABEL_ALONG( XC, YC, TC, T ) plots and labels points at parameter T along a parametric curve (XC, YC, TC). The text labels are nicely offset from the curve.

[HL, HT] = PTLABEL_ALONG( XC, YC, TC, T, DST ) as above, but with the label offset distance fraction specified in DST (0.02). The offset distance is specified as a fraction of the X-Axis length. A Positive DST will place the labels on the left side of the curve, negative DST to the right.

[HL, HT] = PTLABEL_ALONG( XC, YC, TC, T, DST, LINESPEC ) as above, but will plot the desired parametric points with line specifier string LINESPEC ('k.').

The line or point plot handle is returned in HL. The text label handle is returned in HT.

If the data or plot aspect ratios change significantly after the call to PTLABEL_ALONG, the text labels may not look properly offset.

License

This software is Copyright (c) Rob McDonald 2021 and is released under the terms specified in the license.