# Connect two points with invisible vector and evenly spaced markers along the vector between them and Access Marking coordinates to draw circles around them.

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Vance Blake on 29 Jun 2020
Commented: Vance Blake on 29 Jun 2020
Hi, I am trying to use elements of this solution https://www.mathworks.com/matlabcentral/answers/233078-how-do-i-get-evenly-spaced-marks-in-my-plots to draw an invisible vector between two points, and then place markers along that vector that are equally spaced in increments of 8 units apart. I think this solution has just about everything I need, except I do not know how to access the markers coordinate data in order to draw circles around them using viscircles. Any help would be greatly appreciated.
% The 2 points I am trying to connect
P_1 = [52.7102,41.0737];
P_2 = [30.5984,56.2307];
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### Accepted Answer

Adam Danz on 29 Jun 2020
Assuming P_1 and P_2 and (x,y) coordinates, the steps are
1. compute slope between the two points
2. choose the number of points beteween and including the end points (see nPoints variable).
3. Given the slope, and point P_1, compute the coordaintes at equally spaced intervals in the direction of P_2.
% P_1 = (x,y)
% P_2 = (x,y)
P_1 = [52.7102,41.0737];
P_2 = [30.5984,56.2307];
plot(P_1(1),P_1(2),'bo')
hold on
plot(P_2(1),P_2(2),'bo')
% Get eq of line
coefs = polyfit([P_1(1),P_2(1)], [P_1(2), P_2(2)],1);
% Get distance
d = sqrt((P_2(1)-P_1(1))^2 + (P_2(2)-P_1(2))^2);
% number of points between and including end points
nPoints = 5;
% Compute distance of each point from P_1
pointDist = linspace(0,d,nPoints);
% Compute (x,y) coordinates of nPoints **in both directions** from P_1
x = P_1(1) + [-1;1].*(pointDist .* sqrt(1/(1+coefs(1)^2)));
y = P_1(2) + [-1;1].*(coefs(1).*pointDist .* sqrt(1/(1+coefs(1)^2)));
% Chose which set of coordinates to use
% Distance should decrease as each coordinate approaches P_2
isDecreasing = all(diff(sqrt((P_2(1)-x).^2 + (P_2(2)-y).^2),1,2) < 0, 2);
x = x(isDecreasing,:);
y = y(isDecreasing,:);
% Add intervals
hold on
plot(x, y, 'r+')
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Vance Blake on 29 Jun 2020
Thank You!

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