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Initial commit of clabel_along an improved clabel for MATLAB
clabel_along( C, X, Y ) labels all contours in C, placing labels at the intersections between the contours and the curve in X, Y. Labels are rotated to align with the contour.
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‎README.md‎

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# MATLAB contour labels along a curve
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The placement of contour labels by MATLAB's `clabel` can be very
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frustrating. Some control can be gained with `'LabelSpacing'`, but
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`clabel` still has a mind of its own. The user can take full control
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with `'manual'` mode, but that doesn't work well in terms of
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automation and consistency.
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This tool, `clabel_along`, allows the user to specify a curve along
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which to place the contour labels.
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![Example clabel_along result](example.png)
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## Example Use
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[c, h] = contour( peaks );
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clabel_along( c, [1 37], [40 1] );
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clabel_along( c, [25 25], [37.5 30] );
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clabel_along( c, [27.5 27.5], [27 25] );
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## Documentation
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H = clabel_along( C, X, Y ) labels all contours in C, placing labels
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at the intersections between the contours and the curve in X, Y.
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Labels are rotated to align with the contour.
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H = clabel_along( C, X, Y, V ) as above, but only labels the contours
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with levels contained in vector V. If V is empty (default), then all
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contours are labeled.
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H = clabel_along( C, X, Y, V, ROTATE ) as above, but ROTATE is a
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boolean flag to enable label rotation. If ROTATE is TRUE (default),
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then the labels are rotated. The rotation angle is based on the slope
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of the contour at the intersection point and is corrected for the
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aspect ratio of the data and the plot.
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If the data or plot aspect ratios change significantly after the call
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to clabel_along, the labels may not look properly aligned.
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The graphics handles for all of the labels are returned in H.
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## Dependencies
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`clabel_along` requires Douglas Schwarz's
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[intersections](https://www.mathworks.com/matlabcentral/fileexchange/11837)
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routine to calculate the intersectinos between the curve and the contours.
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## License
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This software is Copyright (c) Rob McDonald 2021 and is released under the terms specified in the [license](license.txt).
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‎clabel_along.m‎

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function h = clabel_along( c, x, y, varargin )
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%CLABEL_ALONG Label contours along a curve
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% H = CLABEL_ALONG( C, X, Y ) labels all contours in C, placing labels
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% at the intersections between the contours and the curve in X, Y.
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% Labels are rotated to align with the contour.
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%
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% H = CLABEL_ALONG( C, X, Y, V ) as above, but only labels the contours
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% with levels contained in vector V. If V is empty (default), then all
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% contours are labeled.
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%
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% H = CLABEL_ALONG( C, X, Y, V, ROTATE ) as above, but ROTATE is a
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% boolean flag to enable label rotation. If ROTATE is TRUE (default),
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% then the labels are rotated. The rotation angle is based on the slope
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% of the contour at the intersection point and is corrected for the
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% aspect ratio of the data and the plot.
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%
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% If the data or plot aspect ratios change significantly after the call
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% to CLABEL_ALONG, the labels may not look properly aligned.
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%
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% The graphics handles for all of the labels are returned in H.
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%
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% CLABEL_ALONG requires Douglas Schwarz's INTERSECTIONS routine to
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% calculate the intersectinos between the curve and the contours. It is
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% available from the Matlab File Exchange
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% https://www.mathworks.com/matlabcentral/fileexchange/11837
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%
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% Example:
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% [c, h] = contour( peaks );
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% CLABEL_ALONG( c, [1 37], [40 1] );
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% CLABEL_ALONG( c, [25 25], [37.5 30] );
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% CLABEL_ALONG( c, [27.5 27.5], [27 25] );
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%
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% See also CONTOUR, CONTOURF, CONTOURC, CLABEL, INTERSECTIONS, DASPECT, PBASPECT.
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% Rob McDonald
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% [email protected]
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% 25 March 2021 v. 1.0 -- Original version.
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if ( ~exist( 'intersections', 'file' ) )
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error( 'clabel_along:intersections_not_found',...
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'clabel_along could not find intersections.\nIt is available from the MATLAB file exchange:\nhttps://www.mathworks.com/matlabcentral/fileexchange/11837' );
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end
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% Handle values of contours to label. Empty for all (default).
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if ( nargin < 4 )
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v = [];
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else
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v = varargin{1};
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end
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% Handle rotation disabling flag. True to rotate (default).
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if ( nargin < 5 )
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rotate = true;
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else
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rotate = varargin{2};
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end
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% Grab aspect ratios to correct rotation
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% Data aspect ratio
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da = daspect();
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ard = da(2) / da(1);
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% Plot aspect ratio
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pa = pbaspect();
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arp = pa(2) / pa(1);
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% Initialize handle array
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h = [];
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% Loop over contours in c array
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nlimit = size( c , 2 );
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icont = 1;
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while( icont < nlimit )
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% Pull out contour level and number of points in this contour line
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level = c( 1, icont );
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n = c( 2, icont );
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% Only proceed for empty v (all) or contour in v
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if ( isempty( v ) || any( level == v ) )
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% Pick off contour points
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xc = c( 1, icont+1:icont+n );
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yc = c( 2, icont+1:icont+n );
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% Calculate the intersection points between the contours and the
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% guide curve using Douglas Schwarz's routine
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% https://www.mathworks.com/matlabcentral/fileexchange/11837
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[ xint, yint, iout ] = intersections( xc, yc, x, y );
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% Loop over all intersections
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nint = length( xint );
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for iint = 1:nint
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th = 0;
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if ( rotate )
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% Calculate text rotation angle based on curve slope and
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% plot and data aspect ratios.
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iprev = floor( iout( iint ) );
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if ( iprev == length(xc) )
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iprev = iprev - 1;
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end
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inext = iprev + 1;
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% Calculate aspect ratio adjusted slope
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dx = ( xc( inext ) - xc( iprev ) );
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dy = ( yc( inext ) - yc( iprev ) ) * ard * arp;
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% Calculate angle
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th = atan( dy / dx ) * 180.0 / pi;
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end
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hh = text( xint(iint), yint(iint), num2str( level ), 'rotation', th, 'HorizontalAlignment', 'center', 'VerticalAlignment', 'middle' );
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% Append text handle
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h = [h hh];
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end
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end
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% Increment to next contour line
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icont = icont + n + 1;
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end

‎example.png‎

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