Heat map of 2-D scatter plot data

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Kenny Kim
Kenny Kim 2015-5-15
评论： Walter Roberson 2015-5-15
I have a n by 2 matrix called new_data, and I want to make a heat map plotting density of scatter distribution.
I want to add values varying from 0 to 1 to another array called z that has size of (xmax-xmin,ymax-ymin) in which value of 1 would be added to the z component that matches x and y coordinate and add values less than 1 as the distance from the coordinates increase (kind of like dropping ink on paper, and less ink with increasing distance from epicenter).
Here's my code til now:
x = new_data(:,1);
y = new_data(:,2);
z = zeros(round(max(x)) - round(min(x)), round(max(y)) - round(min(y)));
for i = 1:size(new_data,1);
x(i) = x(i) - min(x);
y(i) = y(i) - min(y);
end
for i = 1:size(new_data,1);
z(round(x(i)),round(y(i))) = z(round(x(i)),round(y(i))) + 1;
end
Could anyone help me with this Gaussian value addition or provide any other ideas for plotting scatter density?

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采纳的回答

Walter Roberson
Walter Roberson 2015-5-15
for i = 1:size(new_data,1);
d = sqrt((x(i) - round(x(i))).^2 + (y(i) - round(y(i)).^2); %distance
deltaz = exp(-d); %gets exponentially less with increasing distance
z(round(x(i)),round(y(i))) = z(round(x(i)),round(y(i))) + deltaz;
end
  2 个评论
Kenny Kim
Kenny Kim 2015-5-15
编辑：Kenny Kim 2015-5-15
I tried a modification of your code and it seems to work, except that my new_data has 27000 rows and thus would require 13 hours or more to process it. Changing x to x1 has nothing to do with this.
for i = 1:size(new_data,1);
for j = 1:size(z,1);
for k = 1:size(z,2);
d = sqrt((j - x1(i)).^2 + (k - y1(i)).^2); %distance
if d <= 20
deltaz = exp(-d); %gets exponentially less with increasing distance
z(j,k) = z(j,k) + deltaz;
end
end
end
end
Walter Roberson
Walter Roberson 2015-5-15
Vectorize, Vectorize, Vectorize!
ndrow = size(new_data,1);
zrow = size(z,1);
zcol = size(z,2);
zcolvec = 1 : zcol;
for i = 1 : ndrow;
x1i = x1(i);
y1i = y1(i);
for j = 1 : zrow;
jdist2 = (j-x1i).^2;
d = sqrt(jdist2 + (zcolvec - y1i).^2);
deltaz = exp(-d);
dinrange = d <= 20;
z(j, dinrange) = z(j,dinrange) + deltaz(dinrange);
end
end

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更多回答（1 个）

Image Analyst
Image Analyst 2015-5-15
If you have the Image Processing Toolbox, perhaps one way is to use the distance transform:
numPoints = 30;
x = rand(1,numPoints);
y = rand(1, numPoints);
rows = 240;
columns = 320;
binaryImage = false(rows, columns);
for k = 1 : length(x);
r = ceil(rows * y(k));
c = ceil(columns * x(k));
binaryImage(r, c) = true;
end
imshow(binaryImage);
edm = bwdist(binaryImage);
edmMax = max(edm(:));
edm = edmMax - edm;
imshow(edm, []);
colormap(hot(256));
colorbar;
hold on;
scatter(columns * x, rows * y, '*')

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