Generate a kml file plotting a multi-colored line

I would like to generate a kml file plotting a line where its color is related to a mesaured value in that location. For example:

Lat Lon Concentration

10 70 57

11 71 58

12 72 59

13 73 57

The line should be blue in the begining and end, and red in the location (12; 72) as the concentratoin there is higher.

Answer 1

[Suraj Kumar]

Hi Alessio,

To generate a KML file using MATLAB to plot a line where the colour of the line segments is related to a measured concentration value, go through the following steps and attached code:

1. Setup the data including the longitude, latitude and concentration values. Then normalize the concentration values to colours in a 0-1 range.

minConc = min(concentration); 
maxConc = max(concentration); 
normalizedConc = (concentration - minConc) / (maxConc -     minConc); 

2. Then you can map the concentration to the colours using ‘jet’ colourmap and interpolate the normalized concentration values to RGB colours using the ‘interp1’ function in MATLAB.

cmap = jet(256);  
colors = interp1(linspace(0, 1, size(cmap, 1)), cmap, normalizedConc);

3. Create a new KML file for writing with a standard header structure and create a line segment for each point.

kmlFileName = 'multicolored_line.kml'; 
fid = fopen(kmlFileName, 'w'); 
% KML Header 
fprintf(fid, '<?xml version="1.0" encoding="UTF-8"?>\n'); 
fprintf(fid, '<Document>\n'); 

4. For each line segment define a unique style in the KML file including its colour and width.

fprintf(fid, '<Style id="lineStyle%d">\n', i); 
fprintf(fid, '  <LineStyle>\n'); 
fprintf(fid, '    <color>%s</color>\n', kmlColor); 
fprintf(fid, '    <width>2</width>\n'); 
fprintf(fid, '  </LineStyle>\n'); 
fprintf(fid, '</Style>\n'); 

5. Close the KML file with appropriate footer tags and output the script file.

% KML Footer 
fprintf(fid, '</Document>\n'); 
fprintf(fid, '</kml>\n'); 
fclose(fid); 

To learn more about the ‘jet’ or ‘interp1’ function in MATLAB, kindly go through the documentations linked below:

• https://www.mathworks.com/help/matlab/ref/jet.html
• https://www.mathworks.com/help/matlab/ref/interp1.html

Hope this works for you!