Right Ascension and Declination Parsers

Routines for converting right ascension and declination from degrees or radians into strings and back again. More...

Functions
double	radToDeg (long double angleInRadians)
double	degToRad (long double angleInDegrees)
std::string	lsst.utils::raRadToStr (double raRad)
std::string	lsst.utils::raDegToStr (double raDeg)
std::string	lsst.utils::decRadToStr (double decRad)
std::string	lsst.utils::decDegToStr (double decDeg)
std::string	lsst.utils::raDecRadToStr (double raRad, double decRad)
std::string	lsst.utils::raDecDegToStr (double raDeg, double decDeg)
double	lsst.utils::raStrToRad (std::string raStr, std::string delimiter=":")
double	lsst.utils::raStrToDeg (std::string raStr, std::string delimiter=":")
double	lsst.utils::decStrToRad (std::string decStr, std::string delimiter=":")
double	lsst.utils::decStrToDeg (std::string decStr, std::string delimiter=":")

Detailed Description

Routines for converting right ascension and declination from degrees or radians into strings and back again.

Right ascensions and declinations (raDecs) are easiest read as strings in the form hh:mm:ss.ss +dd:mm::ss.s, but for calculations, they need to be in degrees or radians. These functions perform those calculations. The function names themselves use the following abbreviations

• ra Right Ascension
• dec Declination
• str String
• deg Degrees
• rad Radians.

So, for example raStrToRad() converts a right ascension in the form of a string to radians.

The ouput strings are in fixed length Ra = hh:mm:ss.ss and Dec= +dd:mm::ss.s with all zeros present (not replaced with whitespace).

Input strings must be of a similar format, although some variation is allowed. The default delimiter (the colon) can be supplied as an optional argument

Function Documentation

string lsst::utils::decDegToStr

(

double

decDeg

)

Definition at line 102 of file RaDecStr.cc.

                                    {

    double dec = decDeg;    //Shorthand
    
    string sgn = (dec<0) ? "-" : "+";

    //Rounding the declination prevents 14.999999999 being represented
    //as 14.:59:60.00
    dec = fabs(round(dec*1e6)/1e6);

    int degrees = (int) floor(dec);
    dec -= degrees;

    int min = (int) floor(dec*60);
    dec -= min/60.;

    double sec = dec*3600;
    sec = floor(sec*100)/100.;

    string str = sgn;
    return boost::str(boost::format("%s%02i:%02i:%05.2f") % sgn % degrees % min % sec);
   
}

string lsst::utils::decRadToStr

(

double

decRad

)

Definition at line 97 of file RaDecStr.cc.

                                    {
    return decDegToStr( radToDeg(decRad) );
}

double lsst::utils::decStrToDeg	(	std::string	decStr,
		std::string	delimiter = ":"
	)

Definition at line 195 of file RaDecStr.cc.

                                                            {
    
    //Regex the degrees, minutes and seconds
    string regexStr = "([\\d]+)";
    regexStr.append(delimiter);
    regexStr.append("(\\d+)");
    regexStr.append(delimiter);    
    regexStr.append("([\\d\\.]+)");
    
     //http://www.boost.org/doc/libs/1_40_0/libs/regex/doc/html/boost_regex/captures.html
    static const boost::regex re(regexStr);
    boost::cmatch what;

    if(! boost::regex_search(decStr.c_str(), what, re)) {
        string msg= boost::str(boost::format("Failed to parse %s as a declination") % decStr);
        throw LSST_EXCEPT(except::RuntimeError, msg);
    }  

    //Convert strings to doubles. Automatically pass the exception up the stack
    double degrees = boost::lexical_cast<double>(string(what[1].first, what[1].second));
    double mins = boost::lexical_cast<double>(string(what[2].first, what[2].second));
    double secs = boost::lexical_cast<double>(string(what[3].first, what[3].second));
    
    degrees += ((secs/60.) +mins)/60.;
    
    //Search for the presence of a minus sign. This approach catches the case of -0 degrees
    string pmStr = "^-";
    static const boost::regex pm(pmStr);
    if(boost::regex_search(decStr, pm)) {
        degrees *= -1;
    }
    
    return degrees;
}

double lsst::utils::decStrToRad	(	std::string	decStr,
		std::string	delimiter = ":"
	)

Definition at line 190 of file RaDecStr.cc.

                                                            {
    return degToRad( decStrToDeg(decStr) );
}

double degToRad

(

long double

angleInDegrees

)

Definition at line 67 of file RaDecStr.cc.

                                            {
    const long double pi = 3.141592653589793115997963468544;
    return angleInDegrees * pi / 180.;
}

string lsst::utils::raDecDegToStr	(	double	raDeg,
		double	decDeg
	)

Definition at line 134 of file RaDecStr.cc.

                                                    {
    string val = raDegToStr(raDeg);
    val = val + " "+decDegToStr(decDeg);
    return val;
}

string lsst::utils::raDecRadToStr	(	double	raRad,
		double	decRad
	)

Definition at line 127 of file RaDecStr.cc.

                                                    {
    string val = raRadToStr(raRad);
    val = val + " "+decRadToStr(decRad);
    return val;
}

string lsst::utils::raDegToStr

(

double

raDeg

)

Definition at line 79 of file RaDecStr.cc.

                                 {

    double ra = raDeg;  //Shorthand
    
    //Convert to seconds of arc
    ra = round(ra*1e6)/1e6;
    ra *= 86400/360;
    
    int hr = (int) floor(ra/3600.);
    ra -= hr*3600;
    
    int mn = (int) floor(ra/60.);
    ra -= mn*60;    //Only seconds remain
    
    return str( boost::format("%02i:%02i:%05.2f") % hr % mn % ra);
}

double radToDeg

(

long double

angleInRadians

)

Definition at line 61 of file RaDecStr.cc.

                                            {
    const long double pi = 3.141592653589793115997963468544;
    return angleInRadians * 180./pi;
}

string lsst::utils::raRadToStr

(

double

raRad

)

Convert a right ascension in radians to a string format

Parameters

raRad

Ra in radians

Definition at line 75 of file RaDecStr.cc.

                                   {
    return raDegToStr( radToDeg(raRad) );
}

double lsst::utils::raStrToDeg	(	std::string	raStr,
		std::string	delimiter = ":"
	)

Definition at line 155 of file RaDecStr.cc.

                                                          {
    
    //Regex the hours, minutes and seconds
    string regexStr = "(\\d+)";
    regexStr.append(delimiter);
    regexStr.append("(\\d+)");
    regexStr.append(delimiter);    
    regexStr.append("([\\d\\.]+)");
    
         static const boost::regex re(regexStr);
    boost::cmatch what;
    //This throws an exception of failure. I could catch it, 
    //but I'd only throw it again
    if(! boost::regex_match(raStr.c_str(), what, re)) {
        string msg= boost::str(boost::format("Failed to parse %s as a declination") % raStr);
        throw LSST_EXCEPT(except::RuntimeError, msg);
    }  
       

    //Convert strings to doubles. Again, errors thrown on failure
    double hours = boost::lexical_cast<double>(string(what[1].first, what[1].second));
    double mins = boost::lexical_cast<double>(string(what[2].first, what[2].second));
    double secs = boost::lexical_cast<double>(string(what[3].first, what[3].second));
    
    double raDeg = secs/3600.;
    raDeg += mins/60.;
    raDeg += hours;
    raDeg *= 360./24.;
    
    //printf("%g %g %g --> %g\n", hours, mins, secs, raDeg);
    return raDeg;

}

double lsst::utils::raStrToRad	(	std::string	raStr,
		std::string	delimiter = ":"
	)

Definition at line 150 of file RaDecStr.cc.

                                                          {
    return degToRad( raStrToDeg(raStr) );
}