How manage for loop to calculate distances?

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Guilherme de Melo
Guilherme de Melo 2023-11-17
评论： Dyuman Joshi 2023-11-17
Ran in:
Helo,
I am trying to calculate distance in km using two variables with a set of latitude and longitude. I tried to use the "distance" funtion inside of two for loop but it is giving an error. Code is in follow:
lat= [-8, -8.2, -8.21, -8.34, -8.9];
long = [-18, -18.2, -18.3, -18.4, -18.45];
total=length(lat);
i=0;
j=0
j = 0
for i=1:total
for j=1:total
i=i+1;
j=j+1;
all_distances(:,k)=distance(lat(:,i,j),long(:,i,j),lat(:,i+1,j+1),long(:,i+1,j+1),wgs84Ellipsoid("km"));
end
end
Index in position 3 exceeds array bounds. Index must not exceed 1.
I should have a new "all_distances" variable with 5 values of distance, but it is only showing the error:
Index in position 3 exceeds array bounds (must not exceed 1).
Someone know what is the problem? Thanks in advance!
  1 个评论
Steven Lord
Steven Lord 2023-11-17
Don't try to change the loop variables inside a for loop. On one hand, any changes you make will be thrown away when the next iteration of the loop starts. On the other hand, during the last iteration of the j loop you increment i and j and make j one greater than the length of lat, which seems wrong the way you're trying to use it. You're taking one step off the end of the gangplank, and MATLAB doesn't want to get wet!

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采纳的回答

Dyuman Joshi
Dyuman Joshi 2023-11-17
编辑：Dyuman Joshi 2023-11-17
Ran in:
As the goal here is to find the distance between consecutive points -
%Data
lat= [-8, -8.2, -8.21, -8.34, -8.9];
long = [-18, -18.2, -18.3, -18.4, -18.45];
%Define a reference to find distance as linear distance in km
wgs84 = wgs84Ellipsoid("km");
len = distance(lat(1:end-1), long(1:end-1), lat(2:end), long(2:end), wgs84)
len = 1×4
31.2277 11.0741 18.1132 62.1796
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Guilherme de Melo
Guilherme de Melo 2023-11-17
Yes, its perfect. It worked on my personal code. Thank you very much. Maybe you could edit your main answer to the public understand better the problem. I will accept your answer.

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更多回答（1 个）

Torsten
Torsten 2023-11-17
编辑：Torsten 2023-11-17
I should have a new "all_distances" variable with 5 values of distance, but it is only showing the error:
Why 5 ? You should have 4 + 3 + 2 + 1 = 10 distances if you have 5 positions.
You get a symmetric matrix distance(i,j) where distance(i,j) is the distance from position i to position j.
Maybe "pdist2" is the correct code to use in your case.
In your code, lat and long are arrays of size 1x5. So why do you suddenly use them as three-dimensional arrays in
all_distances(:,k)=distance(lat(:,i,j),long(:,i,j),lat(:,i+1,j+1),long(:,i+1,j+1),wgs84Ellipsoid("km"));
?
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Dyuman Joshi
Dyuman Joshi 2023-11-17
How is "distance" defined in this context?
Is there a mathematical formula you are using as a reference?
Guilherme de Melo
Guilherme de Melo 2023-11-17
Well, distance in km from geographical coordinates (my two variable Lat/Long). Do you know "distance" function of MATLAB? https://www.mathworks.com/help/map/ref/distance.html

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