build a circle using the latitude and longitude values

Hi, I need to build a circle using the latitude and longitude values ​​as the center of the circle.

busStop_latit; %array (28,1)
busStop_long;  %array (28,1)
%latit and long with which I want to use to build the circle

I need to define "true" if new latitude and longitude values ​​are internal to the constructed circle, "false" if these new values ​​are external to the circle. How is it possible to build the circle and write these two conditions in matlab?

latitude;   %matrix (3600,4)
longitude;  %matrix (3600,4)
%i want to use only the 1st column oh the two matrix
pos_busStop=ones(28,1);
distance;   %matrix (3600,4) and I want to use only the 1st column for this mtrix too
idx=zeros(3600,1);
for i=1:3600
 if lat(i,1)<lat_new(1,:) && lon(i,1)<long_new(1,:)
    idx(:,1)=1
 end
 pos_busStop(:,1)==distanza(idx,1);
end 

[Adam Danz]

It sounds like you're trying to detect if a set of (lon,lat) coordinates are within a set distance to a target in which case you don't need to compute a circle. You just need to compute the distance of each (lon,lat) coordinate to the target and determine if it's less than or equal to the specified distance. That can be done using pdist2().

[Angela Marino]

Yes, but i don't know how to write the code

[Adam Danz]

On second thought, pdist2() with 3600 coordinates may overwhelm that function. It would be easiest just to use the euclidean distance equation directly. I'll add a demo in the answers section that you can apply to your data.

Answer 1

[Adam Danz]

Here's a demo that you can apply to your data.

% Define the center of the circle
target = [lon,lat];  % where lon and lat are single, "scalar" values

% Define the radius of the circle (distance from target to furthest accepted point)
r = 12.2; 

% Compute the distance of each (lon,lat) coordinate from target
% lonVec is a vector of longitudinal coordinates
% latVec is a vector of latitudinal coordinates
% hypot(A,B) is a Matlab function that computes the Euclidean distance between (A,B)
dist = hypot(lonVec-target(1), latVec-target(2)); 

% Detect which coordinates are within range
withinRange = dist <= r;   % withinRange is a logical vector the same size as lonVec | latVec

[Angela Marino]

thanks a lot I'll try it!

[Adam Danz]

If you get stuck, provide more detail about your inputs, examples would be best, and show what you tried to do so I can get a sense of what needs corrected.

[Angela Marino]

this is how I modify my code. Because I would like to be evaluated the distance between each row of column 1 of the vector lat (3600*4) with each row of the vector lat_ferm (28 * 1) to find the minimum for everyone and save the position of every minimum value in the "withinRange" vector which must be 3600 rows and 1 column

[Adam Danz]

I can't work with images since I cannot copy-paste code from an image.

Could you provide the variables that define the targets and the variables that define all of the coordinates you're measuring? They could be included in an attached mat file (just those variables) or you might be able to repoduce them here as a formatted comment.

[Angela Marino]

pos_fermateR2=ones(28,1);

% Define the center of the circle
target = [long_ferm(:,1),lat_ferm(:,1)];  % where lon and lat are single, "scalar" values

% Define the radius of the circle (distance from target to furthest accepted point)
r = 12.2*ones(28,1); 

% Compute the distance of each (lon,lat) coordinate from target
% lonVec is a vector of longitudinal coordinates
% latVec is a vector of latitudinal coordinates
% hypot(A,B) is a Matlab function that computes the Euclidean distance between (A,B)
for i=1:3600
   
       
dist = hypot(abs(lon(i,1)-target(:,1)), abs(lat(i,1)-target(:,2))); 

% Detect which coordinates are within range
   % withinRange is a logical vector the same size as lonVec | latVec
  withinRange = dist <= r;
      if veloc(i,1)==0 && veloc(i-1,1)~=0
         pos_fermateR2(:,1)==distanza(withinRange,1);
    end
end

[Adam Danz]

Try using pdist2. Your lat and lon values contain a lot of NaNs which will propagate through to the final output.

target = [long_ferm(:,1),lat_ferm(:,1)];  
dist = pdist2(target, [lon(:,1),lat(:,1)]);
inCirlce = dist <= 12.2; 

inCircle is a matrix of logical values.

size(inCirlce)
ans =
          28        3600

where inCircle(i,j) tells you whether [lon(j,1),lat(j,1)] is within range of the target target(i,:). 1 means in or on cirlce and 0 means outside or NaN value was present.