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 = CApphot:new()
Destruction	Object:delete()

Data Members

This class contains a large number of parameters that describe the measurement. These are used to pass data to and from the photometry functions. See CApphot Data Members. Values returned by the GetImageParams and Measure methods also used class data members and may be retrieved using either the data members or the Accessor Methods below.

Construction

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 data members 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 data members. See CApphot Data Members.
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 data members of similar name.

GetStatusCode

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.

GetErrMsg

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

Accessor Methods

These methods return values of class data members having a similar name.

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. If the bApplyZeroPtErr flag was true, this includes the photometric zero point error set in the nZeroPtErr value. This is identical to the MagError method in previous versions.
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. If the bApplyZeroPtErr flag was true, then this includes the photometric zero point error set in the nZeroPtErr value. This is identical to the MagErrorT method in previous versions.
SNR	Returns the Signal to Noise Ratio of the signal measured inside the object aperture of radius nRadius1.
SNRT	Returns the theoretical Signal to Noise Ratio of the signal measured inside the object aperture of radius nRadius1.