macOS Degrees to Radians

dieseltwitch · Dec 24, 2011

How do I convert Degrees to radians?

I'm wiring a program (Obj-C, command line) to calculate the earths declination at any given day of the year.

The formal is:
Declination Angle = asin(0.39795*cos((0.98563*(DOY - 173))))

I started by trying to evaluate how the computer deals with each ( ) and whats inside of it.

The first part (DOY - 173) is easy

The second part (0.98563 * (DOY - 173)) i run into a little bit of problems as this is degrees but needs to be converted to radians to make cos and asin work properly. right now I found that:
(0.98563 * (DOY - 173)) * (3.14159/180)

works but is their an easier way? I'm going to have a lot of these in the feature todo and would very much like to find an easier way.

Also how do I round values. I'm using float but I read don't need the earths declination down to the millionths of a degree?

I would also like to say thank you to any one who has been helping me in my other post. I hope that I'm not driving anyone nuts. I am actually going some where with this.

lloyddean · Dec 24, 2011

Code:

#include <math.h>				// M_PI

float RadiantoDegree(float radian)
{
    return ((radian / M_PI) * 180.0f);
}

float DegreetoRadian(float degree)
{
    return ((degree / 180.0f) * M_PI);
}

dieseltwitch · Dec 24, 2011

Ok so I think I understand this as a way to put in an argument that is a radian and get out a degree with out having to re-write it over and over.... my question is how do I employ it? I'm still new enough that I don't know how to call stuff correctly.

here is what I tried....

I get nothing in output, even with the NSLog... How come?

Code:

#import <Foundation/Foundation.h>
#import <math.h>
int main (int argc, const char * argv[])
{

    @autoreleasepool {
        float radian, degree;
        
        
        float RadiantoDegree(float radian);
        {
            return ((radian / M_PI)*180.0f);
        
        }
        float DegreetoRadian(float degree);
        {
            return ((degree / 180.0f)*M_PI);
        }
        
        float myTest,myInput;
        
        myInput = 5.0f;
        
        myTest = RadiantoDegree(myInput);
        NSLog(@"%f",myTest);
        
        
    }
    return 0;
}

lloyddean · Dec 24, 2011

Code:

#import <Foundation/Foundation.h>
#import <math.h>
        
        
float RadiantoDegree(float radian)
{
	return ((radian / M_PI) * 180.0f);
}

float DegreetoRadian(float degree)
{
	return ((degree / 180.0f) * M_PI);
}

int main (int argc, const char * argv[])
{

    @autoreleasepool {
        float radian, degree;
        
        degree = RadiantoDegree(radian);
        radian = DegreetoRadian(degree);
    }

    return 0;
}

dieseltwitch · Dec 24, 2011

Umm when i copy that directly I get these errors...

PS. you don't have to respond to night, unless you a nerd like I am and will stay up all night programing

lloyddean · Dec 24, 2011

My mistake - changed code above!

Senor Cuete · Dec 25, 2011

How about:

double Radians(double x) /*decimal degrees to radians*/
{
return(x * 0.017453293);
}

double Degrees(double x) /*converts radians to decimal degrees*/
{
return(x * 57.29577952);
}

or:

//M_PI defined in math.h:
#include <math.h>

double decimalDegreesToRadians(double x)
{
return(x/360.0 * (2.0 * M_PI));
}

double radiansToDecimalDegrees(double x)
{
return(x / (2.0 * M_PI) * 360.0);
}

You could optimize the second two functions by replacing the (2.0 * M_PI) with 6.2831853071795862. I just copied the first two functions from an astronomy program, so check to see if they're correct. If a type double is the default floating point type for your processor you should do the calculations as a double. There would be no performance advantage in using a smaller type such as a float.

JoshDC · Dec 25, 2011

Senor Cuete said:
You could optimize the second two functions by replacing the (2.0 * M_PI) with 6.2831853071795862.

The compiler will do this for you (gcc and clang do so even with "no optimizations"), so you'll only be making your function less readable.

GorillaPaws · Dec 25, 2011

JoshDC said:
The compiler will do this for you (gcc and clang do so even with "no optimizations"), so you'll only be making your function less readable.

Exactly. One should never use "magic numbers" in their code.

robvas · Dec 26, 2011

dieseltwitch said:
How do I convert Degrees to radians?

You can use this macro:

#define Deg_to_Rad(X) (X*M_PI/180.0)

Also how do I round values. I'm using float but I read don't need the earths declination down to the millionths of a degree?

floor() and ceil()

http://stackoverflow.com/questions/485525/round-for-float-in-c

Be careful working with floating point numbers, though! They are tricky.

http://www.codeproject.com/KB/recipes/float_point.aspx

Sander · Dec 27, 2011

You can use this macro:

#define Deg_to_Rad(X) (X*M_PI/180.0)

Always use extra parentheses in macro arguments:

Code:

#define DEG2RAD(X) ([b]([/b]X[b])[/b]*M_PI/180)

Consider what happens if I use the former with an expression instead of a constant:

Code:

double rad = Deg_to_Rad(deg + 45);

jiminaus · Dec 27, 2011

Or don't use macros. Use inline functions.

Senor Cuete · Dec 27, 2011

dieseltwitch said:
Also how do I round values. I'm using float but I read don't need the earths declination down to the millionths of a degree?

Generally you calculate such things to the maximum precision available to avoid rounding errors and display them as a lower precision when you show them to the user.

This probably means calculating them as doubles, not floats.

Search

Search

macOS Degrees to Radians

dieseltwitch

macrumors regular

lloyddean

macrumors 65816

dieseltwitch

macrumors regular

lloyddean

macrumors 65816

dieseltwitch

macrumors regular

lloyddean

macrumors 65816

Senor Cuete

macrumors 6502

JoshDC

macrumors regular

GorillaPaws

macrumors 6502a

robvas

macrumors 68040

Sander

macrumors 6502a

jiminaus

macrumors 65816

Senor Cuete

macrumors 6502

Our Staff