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)
double	sexagesimalStrToDecimal (std::string inStr, std::string delimiter)
	Convert a sexagesimal string to a decimal double. More...
std::string	lsst.utils::raRadToStr (double raRad)
	Convert a right ascension in radians to a string format. More...
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

std::string lsst::utils::decDegToStr

(

double

decDeg

)

Definition at line 101 of file RaDecStr.cc.

                                       {

    double dec = decDeg;    //Shorthand

    std::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.;

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

}

std::string lsst::utils::decRadToStr

(

double

decRad

)

Definition at line 96 of file RaDecStr.cc.

                                       {
    return decDegToStr( radToDeg(decRad) );
}

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

Definition at line 215 of file RaDecStr.cc.

                                                            {
    return sexagesimalStrToDecimal(decStr, delimiter);
}

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

Definition at line 210 of file RaDecStr.cc.

                                                            {
    return degToRad( decStrToDeg(decStr, delimiter) );
}

double degToRad

(

long double

angleInDegrees

)

Definition at line 66 of file RaDecStr.cc.

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

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

Definition at line 133 of file RaDecStr.cc.

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

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

Definition at line 126 of file RaDecStr.cc.

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

std::string lsst::utils::raDegToStr

(

double

raDeg

)

Definition at line 78 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 boost::str( boost::format("%02i:%02i:%05.2f") % hr % mn % ra);
}

double radToDeg

(

long double

angleInRadians

)

Definition at line 60 of file RaDecStr.cc.

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

std::string lsst::utils::raRadToStr

(

double

raRad

)

Convert a right ascension in radians to a string format.

Parameters

raRad

Ra in radians

Definition at line 74 of file RaDecStr.cc.

                                      {
    return raDegToStr( radToDeg(raRad) );
}

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

Definition at line 199 of file RaDecStr.cc.

                                                          {
    double ra_hours = sexagesimalStrToDecimal(raStr, delimiter);
    if (ra_hours < 0) {
      std::string msg= boost::str(boost::format("Right ascension %s is negative!") % raStr);
      throw LSST_EXCEPT(except::RuntimeError, msg);
    }

    return ra_hours * (360.0/24.0);  // hours to degrees
}

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

Definition at line 194 of file RaDecStr.cc.

                                                          {
    return degToRad( raStrToDeg(raStr, delimiter) );
}

double sexagesimalStrToDecimal	(	std::string	inStr,
		std::string	delimiter
	)

Convert a sexagesimal string to a decimal double.

Helper function to parse sexagesimal string in either hours:minutes:seconds or degrees:minutes:seconds, and then convert this to a decimal double. Note that no conversion between hours and degrees is performed.

Parameters

inStr	String to parse and convert
delimiter	Delimiter separating minutes and seconds from hours or degrees.

Definition at line 156 of file RaDecStr.cc.

  {
    // Regex the hh:mm:ss or dd:mm:ss with delimiter.
    std::string regexStr = "(\\d+)";
    regexStr.append(delimiter);
    regexStr.append("(\\d+)");
    regexStr.append(delimiter);
    regexStr.append("([\\d\\.]+)");

    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_search(inStr.c_str(), what, re)) {
        std::string msg= boost::str(boost::format(
            "Failed to parse %s as a right ascension or declination with regex %s")
            % inStr % regexStr);
        throw LSST_EXCEPT(except::RuntimeError, msg);
    }

    //Convert strings to doubles. Again, errors thrown on failure
    double hh_or_dd = std::stod(std::string(what[1].first, what[1].second));
    double mm = std::stod(std::string(what[2].first, what[2].second));
    double ss = std::stod(std::string(what[3].first, what[3].second));

    hh_or_dd += (mm + ss/60.0)/60.0;

    //Search for leading - sign.
    std::string pmStr = "^-";
    static const boost::regex pm(pmStr);
    if(boost::regex_search(inStr, pm))
        hh_or_dd *= -1;
    return hh_or_dd;
}