Package astLib :: Module astCoords

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Module astCoords

source code

module for coordinate manipulation (conversions, calculations etc.)

http://astlib.sourceforge.net

Functions

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float

hms2decimal(RAString, delimiter)
Converts a delimited string of Hours:Minutes:Seconds format into decimal degrees.

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float

dms2decimal(decString, delimiter)
Converts a delimited string of Degrees:Minutes:Seconds format into decimal degrees.

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string

decimal2hms(RADeg, delimiter)
Converts decimal degrees to string in Hours:Minutes:Seconds format with user specified delimiter.

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string

decimal2dms(decDeg, delimiter)
Converts decimal degrees to string in Degrees:Minutes:Seconds format with user specified delimiter.

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tuple

eq2cart(RA, DEC, r)
Convert Equatorial coordinates to Cartesian coordinates.

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tuple

cart2eq(x, y, z)
Convert Cartesian coordinates to Equatorial coordinates.

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float or numpy array, depending upon type of RADeg2, decDeg2

calcAngSepDeg(RADeg1, decDeg1, RADeg2, decDeg2)
Calculates the angular separation of two positions on the sky (specified in decimal degrees) in decimal degrees, assuming a tangent plane projection (so separation has to be <90 deg).

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float [newRA, newDec]

shiftRADec(ra1, dec1, deltaRA, deltaDec)
Computes new right ascension and declination shifted from the original by some delta RA and delta DEC.

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list

convertCoords(inputSystem, outputSystem, coordX, coordY, epoch)
Converts specified coordinates (given in decimal degrees) between J2000, B1950, and Galactic.

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calcSkyArea(RA1, RA2, DEC1, DEC2, units=True)
Calculates the area of the quadrangle on the sky given by the intersection of a right ascension lune and declination zone.

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list

calcRADecSearchBox(RADeg, decDeg, radiusSkyDeg)
Calculates minimum and maximum RA, dec coords needed to define a box enclosing a circle of radius radiusSkyDeg around the given RADeg, decDeg coordinates.

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aitoff(lon, lat)
Make Aitoff map projection.

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Function Details

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hms2decimal(RAString, delimiter)

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Converts a delimited string of Hours:Minutes:Seconds format into decimal degrees.

Parameters:

RAString (string) - coordinate string in H:M:S format
delimiter (string) - delimiter character in RAString

Returns: float

coordinate in decimal degrees

dms2decimal(decString, delimiter)

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Converts a delimited string of Degrees:Minutes:Seconds format into decimal degrees.

Parameters:

decString (string) - coordinate string in D:M:S format
delimiter (string) - delimiter character in decString

Returns: float

coordinate in decimal degrees

decimal2hms(RADeg, delimiter)

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Converts decimal degrees to string in Hours:Minutes:Seconds format with user specified delimiter.

Parameters:

RADeg (float) - coordinate in decimal degrees
delimiter (string) - delimiter character in returned string

Returns: string

coordinate string in H:M:S format

decimal2dms(decDeg, delimiter)

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Converts decimal degrees to string in Degrees:Minutes:Seconds format with user specified delimiter.

Parameters:

decDeg (float) - coordinate in decimal degrees
delimiter (string) - delimiter character in returned string

Returns: string

coordinate string in D:M:S format

eq2cart(RA, DEC, r)

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Convert Equatorial coordinates to Cartesian coordinates. Return a tuple (x, y, z) in the same unit of the input distance. This is the inverse of cart2eq.

Parameters:

RA (float) - Right Ascension in decimal degrees
DEC (float) - Declination in decimal degrees
r (float) - Distance to the object.

Returns: tuple

Tuple of (x, y, z) in same unit as the input distance.

cart2eq(x, y, z)

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Convert Cartesian coordinates to Equatorial coordinates. Returns a tuple of (RA, DEC, r), with RA and DEC given in decimal degrees and r in the same unit as the input.

Parameters:

x (float) - x coordinate
y (float) - x coordinate
z (float) - x coordinate

Returns: tuple

Tuple of (RA, DEC, r)

calcAngSepDeg(RADeg1, decDeg1, RADeg2, decDeg2)

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Calculates the angular separation of two positions on the sky (specified in decimal degrees) in decimal degrees, assuming a tangent plane projection (so separation has to be <90 deg). Note that RADeg2, decDeg2 can be numpy arrays.

Parameters:

RADeg1 (float) - R.A. in decimal degrees for position 1
decDeg1 (float) - dec. in decimal degrees for position 1
RADeg2 (float or numpy array) - R.A. in decimal degrees for position 2
decDeg2 (float or numpy array) - dec. in decimal degrees for position 2

Returns: float or numpy array, depending upon type of RADeg2, decDeg2

angular separation in decimal degrees

shiftRADec(ra1, dec1, deltaRA, deltaDec)

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Computes new right ascension and declination shifted from the original by some delta RA and delta DEC. Input position is decimal degrees. Shifts (deltaRA, deltaDec) are arcseconds, and output is decimal degrees. Based on an IDL routine of the same name.

Parameters:

ra1 (R.A. in decimal degrees) - float
dec1 (dec. in decimal degrees) - float
deltaRA (shift in R.A. in arcseconds) - float
deltaDec (shift in dec. in arcseconds) - float

Returns: float [newRA, newDec]

shifted R.A. and dec.

convertCoords(inputSystem, outputSystem, coordX, coordY, epoch)

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Converts specified coordinates (given in decimal degrees) between J2000, B1950, and Galactic.

Parameters:

inputSystem (string) - system of the input coordinates (either "J2000", "B1950" or "GALACTIC")
outputSystem (string) - system of the returned coordinates (either "J2000", "B1950" or "GALACTIC")
coordX (float) - longitude coordinate in decimal degrees, e.g. R. A.
coordY (float) - latitude coordinate in decimal degrees, e.g. dec.
epoch (float) - epoch of the input coordinates

Returns: list

coordinates in decimal degrees in requested output system

calcSkyArea(RA1, RA2, DEC1, DEC2, units=True)

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Calculates the area of the quadrangle on the sky given by the intersection of a right ascension lune and declination zone. By default, the area is returned in square degrees.

Parameters:

RA1 (float) - Right ascension in decimal degrees
RA2 (float) - Right ascension in decimal degrees
DEC1 (float) - Declination in decimal degrees
DEC2 (float) - Declination in decimal degrees
units (bool) - True: Area is given in square degrees. False: Area is given as a fraction of the total sky.

calcRADecSearchBox(RADeg, decDeg, radiusSkyDeg)

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Calculates minimum and maximum RA, dec coords needed to define a box enclosing a circle of radius radiusSkyDeg around the given RADeg, decDeg coordinates. Useful for freeform queries of e.g. SDSS, UKIDSS etc.. Uses calcAngSepDeg, so has the same limitations.

Parameters:

RADeg (float) - RA coordinate of centre of search region
decDeg (float) - dec coordinate of centre of search region
radiusSkyDeg (float) - radius in degrees on the sky used to define search region

Returns: list

[RAMin, RAMax, decMin, decMax] - coordinates in decimal degrees defining search box

aitoff(lon, lat)

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Make Aitoff map projection.

Take traditional longitude and latitude in radians and return a tuple (x, y).

Notice that traditionally longitude is in [-pi:pi] from the meridian, and latitude is in [-pi/2:pi/2] from the equator. So, for example, if you would like to make a galactic map projection centered on the galactic center, before passing galactic longitude l to the function you should first do: l = l if l <= numpy.pi else l - 2 * numpy.pi

Keyword arguments: lon -- Traditional longitude in radians, in range [-pi:pi] lat -- Traditional latitude in radians, in range [-pi/2:pi/2]