CApphot Class Description
The CApphot class manages the operation of
aperture photometry routines. These routines are used for computing
the total brightness of a point sources. For astronomical
applications, this is used to measure stars and other objects that
are unresolved or of small angular extent. The aperture may be a
circle or an ellipse. The background is subtracted from the
measurement and may be computed locally or assigned a specified
value.
Usage
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Construction
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Object = new_apphot()
Object = CApphot:new()
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Destruction
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Object:delete()
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Properties
This class contains numerous properties that
describe the measurement. These are used to pass data to and from
the photometry functions. See CApphot Properties. Values returned by the
GetImageParams and Measure methods also used class properties and
may be retrieved using either the properties or the Accessor Methods
below.
Creation - Non-class Functions
This function is normally used to create a new
CApphot object as an alternative to the class-based
new method.
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new_apphot
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Creates a new instance of a CApphot object.
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Construction and Destruction - Class Methods
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new
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Creates a new instance of the CApphot
class. There are 2 constructor formats.
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delete
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Deletes the instance of the CApphot
object.
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Copy
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Copies the properties of this CApphot object to a
new CApphot object.
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Operations
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GetImageParams
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Reads the image header and fetches the values of
camera gain, readout noise, exposure time, and the photometric zero
point and its error. These values are returned as class properties.
See CApphot
Properties.
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Measure
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Performs an aperture photometry measurement at a
(column,row) coordinate in an image.
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SetBgMethod
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Sets the method used to evaluate the background in
the Measure method. Four options are provided: mean, median,
mode, and value.
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The following table describes "accessor" methods
that return the parameters of a measurement. These methods return
CApphot
properties of similar name.
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GetStatusCode
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Returns an integer number indicating the status
returned by the Measure and GetImageParams methods.
 The
Measure method
returns false if an
error occurred. A negative error number can be retrieved using
GetStatusCode.
The
GetImageParams method returns false if an error occurred.
The various errors are bit-wide OR-ed into a single positive number
which is returned by GetStatusCode. The errors may be sorted
out using the BitTest
function.
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GetErrMsg
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Returns a string indicating "Success" or the error
message generated by the photometry method (see GetStatusCode).
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Accessor Methods
These methods return (access) the values of
class
properties.
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X
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Returns the X position of the center of the
measuring apertures.
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Y
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Returns the Y position of the center of the
measuring apertures.
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NetCount
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Returns the net count for the object, measured in
counts (or "ADU" or "DN"). If the bRemoveBg flag is true, this is the net count above
the background. Otherwise, this gives the total count above
zero.
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NetCountErr
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Returns the uncertainty in the net count for the
object, measured in counts (or "ADU" or "DN").
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NetCountErrT
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Returns the theoretical uncertainty in the net
count for the object, measured in counts (or "ADU" or "DN").
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BgValue
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Returns the background value per pixel, measured
in counts (or "ADU" or "DN"). If the bRemoveBg flag is true, this value was subtracted
from the total to calculate nNetCount.
This is identical to the BgCount method in previous
versions.
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BgValueErr
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Returns the error in the background value (per
pixel). This is a 1-sigma mean error, not the error of the mean
background, and is measured in units of counts (or "ADU" or "DN").
If the bRemoveBg flag is true, this
value was subtracted from the total count to calculate nNetCount. This is identical to the
BgCountErr method in previous versions.
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Mag
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Returns the measured magnitude of the object. If
the bApplyZeroPt flag was true, this
includes the photometric zero point set in the nZeroPt value.
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MagErr
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Returns the random error in the value of
nMag as calculated from the noise
measured in the background sample. This method returns the class
property nMagErr. To include the
uncertainty of the photometric zero point in this returned error,
specify a non zero vbalue for nZeroPtErr.
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MagErrT
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Returns the theoretical random error in the value
of nMag as calculated using only the
instrumental values but not the actual noise measured in the
background sample. This method returns the class property
nMagErrT. To include the uncertainty of
the photometric zero point in this returned error, specify a non
zero vbalue for nZeroPtErr.
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SNR
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Returns the Signal to Noise Ratio of the signal
measured inside the object aperture of radius nRadius1. This method returns the class property
nSnRatio.
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SNRT
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Returns the theoretical Signal to Noise Ratio of
the signal measured inside the object aperture of radius
nRadius1. This method returns the class
property nSnRatioT.
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Related Topics
Script
Classes, CImage
class, CalcAirmass, CalcJD, CalcHJD
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