How to create a 2d colormap having temperature reading at specific Longitudes and Latitudes

I have a 3 column matrix, lat,long and temperature. I want to create a color map of the country in which these readings are taken from. I dont have readings at every long/lat only about 79 locations within the country. I need to interpolate somehow so that the readings cover not only that specific spot but an area so that the whole country can be depicted in the colormap. I am able to call for the country using the following

worldmap({'Haiti','Dominican Republic'}) >> load coast >> plotm(lat, long)

that gives me an outline of the islands i am working with. Now i need to use the matrix (with 79 specific sites each defined by lat,lon and temperature) to show the avg temperature for that year.

PLEASE HELP i have been googling for hours, everything i find is people who have the third variable at every location for the area they are working with.

any help would be EXTREMELY appreciated.

Answer 1

[Youssef Khmou]

Cristina,

Here is an alternative approach, the third column represents the color, but it is not easy to create a color map ( you can create linear scale of colors independently), a color is 3by1 vector , we choose two values randomly and we fix the third as value of Temperature :

%  Plotting longitude latitude and temperature on map 
%worldmap({'Haiti','Dominican Republic'});
%load coast;
%plotm(lat, long);
hold on;
% Example of the matrix 
M(:,1)=floor(100*randn(79,1));
M(:,2)=floor(100*randn(79,1));
M(:,3)=floor(100*rand(79,1));

 %  the third column is temperature it represents the color, we need to
 %  normalize it
 M(:,3)=M(:,3)./max(M(:,3));
 axesm sinusoid;
 for n=1:79
 plotm(M(n,1),M(n,2),'o','MarkerFaceColor',[0.5 0.5 M(n,3)],'MarkerSize',12);
 end
 % values 0.5 are arbitrary , you can change them ( RGB).

[Cristina]

Thank you so much for responding, i tried this but it does not plot on the map plot. And in this case where do I input the temperature so that it creates randn based on the value that was recorded. Im new to MATLAB. I appreciate your help.

[Youssef Khmou]

you are welcome, i only used randn to simulate the 79x3 matrix that you have, did you relpace M with your matrix? you can post your matrix as M-file?

Answer 2

[Walter Roberson]

If you have a quite new MATLAB then see ScatteredInterpolant or possibly better for you, GriddedInterpolant. If you have a little older MATLAB see TriScatteredInterp .

[Cristina]

In this case should i make x a matrix of 2 rows (lat, lon)? I was reading examples and the way the geoid for example is loaded is a 180x360 matrix (1 degree per cell) so I want to make a matrix at about .1 per cell since its a small location from about 12-22N latitude and 65-77W longitude. I have 79 values for temperature at 79 locations. I want to use those temperatures with their corresponding coordinates to interpolate so that i can fill that matrix and then use it the way the geoid is used. This may be a strange way to go about it but because i am not familiar with MATLAb this seems to be the only way that makes sense to me.

[Cristina]

I am unclear because V (in my case temperature) is not a function of X,Y (lat, long) its just a reading i have. Also i am unclear how to defien xq yq to get vq.