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Getting odd floating point results.

Nick S over 16 years ago

((lat2-lat1)*BETA*(lat2-lat1)*BETA + (long2-long1)*delta*(long2-long1)*delta)

I'm writing some C code and I am getting some screwy results. Basically lat1, lat2, long1, long2 are all latitudes and longitudes in radians, delta is another precalculated parameter. BETA is a defined constant.

As far as I can tell this code always results in an answer equal to BETA regardless of changing inputs. Additionally when I brake out the two addition terms: (lat2-lat1)*BETA*(lat2-lat1)*BETA and (long2-long1)*delta*(long2-long1)*delta), and compute them separately I get a result of "0". I have been trying to wrap my head around what is wrong without success for a day now. Any suggestions for things to try would be appreciated.

Thanks in advance.

Parents

0 ashley madison over 16 years ago in reply to Nick S

FWIW, here's the code I used to test:

#include <reg52.h>
#include <math.h>
#include <intrins.h>

#define ALPHA 6378137.0
#define BETA  6356752.0

float procedure( float lat1, float long1, float lat2, float long2 ) {
    float delta;
    delta = ALPHA * cos(lat1);
    return ((lat2-lat1)*BETA*(lat2-lat1)*BETA + (long2-long1)*delta*(long2-long1)*delta);
}

void main(void)
{
    float f;

    f = procedure(0.727414575, -1.24152067, 0.727336559, -1.24135643);

    for (;;) {
        _nop_();
    }
}

Reply

0 ashley madison over 16 years ago in reply to Nick S

FWIW, here's the code I used to test:

#include <reg52.h>
#include <math.h>
#include <intrins.h>

#define ALPHA 6378137.0
#define BETA  6356752.0

float procedure( float lat1, float long1, float lat2, float long2 ) {
    float delta;
    delta = ALPHA * cos(lat1);
    return ((lat2-lat1)*BETA*(lat2-lat1)*BETA + (long2-long1)*delta*(long2-long1)*delta);
}

void main(void)
{
    float f;

    f = procedure(0.727414575, -1.24152067, 0.727336559, -1.24135643);

    for (;;) {
        _nop_();
    }
}

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