For loop not working as desired

Hi,

I am calculating the distance and velocity between GPS coordinates (lat,long,height) and it appears to work well when I used single values. However, I have a matrix of 79 GPS coordinates (3x79 matrix) and I want to find the distance and speed between each two consecutive points. When I try to use a for loop the output I get is all zeros apart from the first and last value.

I am probably doing something silly but I can spot it...any suggestions are appreciated :)

for k=1:77

    R=6378.1e3; 
    latDistance = copter_llh(1,k+1) - copter_llh(1,k);
    lonDistance = copter_llh(2,k+1) - copter_llh(2,k);
    a = sin(latDistance / 2) * sin(latDistance / 2) + cos(copter_llh(1,k))...
        *cos(copter_llh(1,k+1)) * sin(lonDistance / 2) * sin(lonDistance / 2);
    c = 2 *atan2(sqrt(a), sqrt(1 - a));
    distance = R * c * 1000; % convert to meters

    height = copter_llh(3,k+1) - copter_llh(3,k);
    distance = sqrt((distance^ 2) + (height^2));
    velocity = distance/0.1*60; % stepsize =0.1min ___speed in m/s
    distance(:,k)=(distance);
    velocity(:,k)=(velocity);

end

[dpb]

Start with the deltas can be gotten entirely out of the loop...

lat=diff(copter_llh(1,:),1,2);
lon=diff(copter_llh(2,:),1,2);
ht=diff(copter_llh(3,:),1,2);

The above does all 78 differences for a 79-column array; your loop only will return 77 differences from 2-1 thru 78-77; I'm not understanding the why of that; perhaps there's something irregular in the last column or it wraps around or something???

After that, the products can be computed with .* "dot" operator if you fix the lengths to be consistent and the distance computed from the dot multiply of the vectors as well.

Should be able to eliminate the loop entirely.

Answer 1

[Star Strider]

I can’t run your code, but one item that would seem to be a problem is:

    distance = sqrt((distance^ 2) + (height^2));
    velocity = distance/0.1*60; % stepsize =0.1min ___speed in m/s
    distance(:,k)=(distance);
    velocity(:,k)=(velocity);

You’re assigning ‘distance’ and ‘velocity’ scalars and then as arrays. Won’t work. This example illustrates the same problem:

for k1 = 1:10
    xt = k1^2;
    xt(k1) = xt;
end

Renaming the scalar solves the problem:

for k1 = 1:10
    xt2 = k1^2;
    xt(k1) = xt2;
end

[Buzz]

Yeah, thank you. Whoops..

[Star Strider]

My pleasure!