advanced Heatmap plotting question

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chang liu
chang liu 2020-8-21
评论： chang liu 2020-8-31
hi matlab experts, i have the following data matrix (see attached data.mat file)
i don't care about the all 0 column.
first column is x coordinate, second is y coordinate.
4th column is the value
as you can tell this is some sort of a scan that covers a 30x30 xy area
so for example, the first row of this data is -15,-15,0, 2921. it means, at x= -15 and y= -15, the data value is 2921 (ignore the 0)
question:
1) how do you plot a simple heatmap using this data?
2) more difficult: i really care about the values that are less than 3000. for me, any value less than 3000 means 'valid', any value above 3000 is invalid. so in addition to a normal heatmap that will just display the values in a temperature sense (like from cool to hot) , i really want another graph that clearly shows me what areas are 'valid' and what areas are 'invalid' in a black and white color sense (or green/red, whatever, as long as its just two colors) . one that i could easily look at and say, hey, at x=5 y=5, the value is invalid (above 3000)
thanks a lot!

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回答（1 个）

Alan Stevens
Alan Stevens 2020-8-21
The following will do it, though there are probably neater ways to do the colouring:
load('data.mat')
x = Z0(:,1); y = Z0(:,2); z = Z0(:,4);
x = reshape(x,31,31); y = reshape(y,31,31);z=reshape(z,31,31);
zlo = z<=3000;
C = 100*zlo;
surf(x,y,z,C)
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Alan Stevens
Alan Stevens 2020-8-27
If you add the colormap command just before the surf command like so:
...
C = 100*zlo;
colormap([0 0 0; 1 1 1]);
surf(x,y,z,C)
...
you will just get two colours (or just one for some situations!) .
The colormap above will result in black (the [0 0 0]) and white (the [1 1 1])..
By changing the values in the second row (i.e. the [1 1 1] values) you can adjust the colour (each of the digits must be between 0 and 1: they are RGB values). For example [127/255 1 212/255] is aquamarine (I can't think what yellow is off the top of my head).

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