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

Construction

Object = new_apphot()

Object = CApphot:new()

Destruction

Object:delete()

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.

new_apphot

Creates a new instance of a CApphot object.

Construction and Destruction - Class Methods

new

Creates a new instance of the CApphot class. There are 2 constructor formats.

delete

Deletes the instance of the CApphot object.

Copy

Copies the properties of this CApphot object to a new CApphot object.

Operations

GetImageParams

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.

Measure

Performs an aperture photometry measurement at a (column,row) coordinate in an image.

SetBgMethod

Sets the method used to evaluate the background in the Measure method. Four options are provided: mean, median, mode, and value.

The following table describes "accessor" methods that return the parameters of a measurement. These methods return CApphot properties of similar name.

GetStatusCode

Returns an integer number indicating the status returned by the Measure and GetImageParams methods.

bullet.gif    The Measure method returns false if an error occurred. A negative error number can be retrieved using GetStatusCode.

bullet.gif    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.

GetErrMsg

Returns a string indicating "Success" or the error message generated by the photometry method (see GetStatusCode).

Accessor Methods

These methods return (access) the values of class properties.

X

Returns the X position of the center of the measuring apertures.

Y

Returns the Y position of the center of the measuring apertures.

NetCount

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.

NetCountErr

Returns the uncertainty in the net count for the object, measured in counts (or "ADU" or "DN").

NetCountErrT

Returns the theoretical uncertainty in the net count for the object, measured in counts (or "ADU" or "DN").

BgValue

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.

BgValueErr

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.

Mag

Returns the measured magnitude of the object. If the bApplyZeroPt flag was true, this includes the photometric zero point set in the nZeroPt value.

MagErr

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.

MagErrT

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.

SNR

Returns the Signal to Noise Ratio of the signal measured inside the object aperture of radius nRadius1. This method returns the class property nSnRatio.

SNRT

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.

Related Topics

Script Classes, CImage class, CalcAirmass, CalcJD, CalcHJD


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