i have number of points that have (x,y) .then i define a line and i want to realize which points are under the line?
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i have number of points that have (x,y) .then i define a line and i want to realize which points are under the line?
i write this :
....
r=[0 10 15 20 30];
t=[10 10 15 10 10];
f= line(r,t)
axis([0,30,0,20]);
d=(eldof(:,10))& (eldof(:,11)) <= f
then all of points are zero
why??
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Réponse acceptée
Image Analyst
le 18 Avr 2020
You need to call polyfit:
coefficients = polyfit(r, t, 1);
or you can call fitPolynomialRansac if you want the line to go exactly through the points on the bottom of your plot.
Then you have to get some x values and get a digital vector of line values. You can use your r locations, or you can use more or less than that. Then see which values are less than the y value of the line. For the same r points
yLine = polyval(coefficients, r);
belowLine = t < yLine; % A logical index vector.
2 commentaires
Image Analyst
le 20 Avr 2020
Those points are just a grid:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/285986/image.png)
I'm not sure what to do either. Can you draw the line on there that you want to detect if some point is below that line, and repost your picture with the line indicated?
Plus de réponses (1)
Mili Kian
le 21 Avr 2020
2 commentaires
Image Analyst
le 21 Avr 2020
Try this:
xy = [...
1 1
1 3
1 5
1 7
1 9
1 11
1 13
1 15
1 17
3 1
3 3
3 5
3 7
3 9
3 11
3 13
3 15
3 17
5 1
5 3
5 5
5 7
5 9
5 11
5 13
5 15
5 17
7 1
7 3
7 5
7 7
7 9
7 11
7 13
7 15
7 17
9 1
9 3
9 5
9 7
9 9
9 11
9 13
9 15
9 17
11 1
11 3
11 5
11 7
11 9
11 11
11 13
11 15
11 17
13 1
13 3
13 5
13 7
13 9
13 11
13 13
13 15
13 17
15 1
15 3
15 5
15 7
15 9
15 11
15 13
15 15
15 17
17 1
17 3
17 5
17 7
17 9
17 11
17 13
17 15
17 17];
x = xy(:, 1);
y = xy(:, 2);
plot(x, y, 'b.', 'MarkerSize', 20);
grid on;
% Make line
xRedLine = unique(x)
redLine = [8, 8, 8, 10, 13.1, 10, 8, 8, 8];
hold on;
plot(xRedLine, redLine, 'r+-', 'LineWidth', 3, 'MarkerSize', 15);
% Find values less than the red line for each x and plot a red square around them
for k = 1 : length(x)
thisX = round(x(k))
index = find(thisX == xRedLine);
if y(k) < redLine(index)
plot(thisX, y(k), 'rs', 'MarkerSize', 20);
end
end
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/286460/image.png)
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