How to loop function for a 2 column matrix

Hi,

I have this calculation here to calculate the distance between 2 points on a globe with their latitudes and longitudes.

[arclen, az] = distance([40.333, -10.036 ], [40.333, -9.46]);

km = deg2km(arclen);

display(km)

This displays:

>> stationdist

km =

   48.8236

However, I have multiple latitudes and longitudes like so:

loc1 = [40.333	-10.036;
40.333	-9.46;
40.333	-9.767;
40.333	-12.219;
41.383	-13.888;
42.581	-15.461;
43.78	-17.032;
45.05	-18.505;
46.544	-19.672;
48.039	-20.848;
49.529	-22.017;
50.278	-22.603;
53.019	-24.752;
55.506	-26.71;
57.004	-27.879;
58.207	-29.725;
58.843	-31.267;
59.102	-33.828;
59.363	-36.397;
59.623	-38.954;
59.773	-41.297;
59.902	-43.015;
59.823	-42.399;
59.799	-42.004;
59.753	-45.112;
59.434	-45.666;
59.068	-46.083;
56.916	-47.422;
55.842	-48.093;
53.692	-49.433;
53	-51.1;]

I need to perform the calculation between each row, then each distance needs to be a sum of itself and previous distances. It should look like this, assuming only 4 columns are used and that stations are calculated to be roughly 50km apart.

>> stationdist

km =

   48.8236
   96.3574
   156.3246
   201.4127

How would I create this loop with my given matrix?

Charlie

Answer 1

[Stephan]

You do not need a loop - the distance function is vectorized and accepts vector-inputs. You simply need to use indexing to get what you want:

[arclen, az] = distance([loc1(1:end-1,1), loc1(1:end-1,2)], [loc1(2:end,1), loc1(2:end,2)]);
km = deg2km(arclen);

This should return a vector of km with all values.

[Charlie Hillary]

Thanks, a lot more simple than prev. thought!

Charlie

Answer 2

[Ameer Hamza]

I don't have the mapping toolbox, so following code is untested

dist = zeros(size(loc1,1)-1,1);
for i = 1:size(loc1,1)-1
    [arclen, az] = distance(loc1(i,:), loc1(i+1,:));
    dist(i) = deg2km(arclen);
end
stationdist = cumsum(dist)

[Charlie Hillary]

Hi Ameer,

This worked great too, thanks a lot. I will now find a way to sum the distances!

Charlie