Centroider

Centroider_Multi

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Last Updated Jan 2001

Purpose :

Find the center of the multiple objects stored in a CIM files.

Procedure :

This routine refuse the objects with one of this caracteristics:

Position of the maximum out of x_boxsize or y_boxsize defined from cim image. (This happen if the cutout was runned in a big object and the cutout take only a part of it)

Classification code defferent from that specified with the option /CLASS_TYPE=a.

Dimension of the cutout bigger than max_size, where max_size is 512x512 matrix.

Cutout with more than 20 blended objects

The total number of objects refused is reported in the DID file. This routine performs a multiple fit to the cutout images with a bidimensional circular gaussian or with a bidimensional elliptical gaussian to find the object center. The routine takes the object cutout stored in the cim file, normalizes the image, and starts the iterations sequence using, as starting point, the baricenter position. The parameters passed to the fit routine (GNTICK) are CENT_TYPE dependent; we have:

Circular Gaussian

number_parameters=4*number_obj+3

centroider_params((k-1)*4+1)=(image_max-bzero)/bscale !amplitude of gaussian

centroider_params((k-1)*4+2)=oop.x_position-cih.lx+1.5 !x position on the cutout

centroider_params((k-1)*4+3)=oop.y_position-cih.ly+1.5 !y position on the cutout

centroider_params((k-1)*4+4)=sqrt((oop.uf_xx+oop.uf_yy)/2.0) !sigma of circular gaussian

Elliptical Gaussian

number_parameters=6*number_obj+3

centroider_params((k-1)*6+1)=(image_max-bzero)/bscale !amplitude of gaussian

centroider_params((k-1)*6+2)=oop.x_position-cih.lx+1.5 !x position on the cutout

centroider_params((k-1)*6+3)=oop.y_position-cih.ly+1.5 !y position on the cutout

centroider_params((k-1)*6+4)=sqrt(oop.uf_xx) !sigma_x of ellipltical gaussian

centroider_params((k-1)*6+5)=sqrt(oop.uf_yy) !sigma_y of ellipltical gaussian

centroider_params((k-1)*6+6)=oop.uf_xy /(sqrt(oop.uf_xx)*sqrt(oop.uf_yy)) !Correlation coefficent

ENDIF

centroider_params(number_parameters-2)=0.001 !background plane x coefficient

centroider_params(number_parameters-1)=0.001 !background plane y coefficient

centroider_params(number_parameters-0)=(skyc-bzero)/bscale !background plane constant

GNTICK stops when one of the following controls are satisfied:

Number of iterations > centroider_option(1) (=NUM_IT_MAX)

[In this case centroider_error=-1]

Difference on the parameters (step i+1 - step i)

[In this case centroider_error=see Output Effects]

Somthing is wrong with the current estimate of one (or more) of the parameters (es. negative sigma, negative intensity at peak ...)

[In this case centroider_error=-2]

Output Effects :

This routine writes out only those quantites newly calcolated or upgrated to pre-existing oop file or to the cen file. These potentially affected variables are (using the oop structure):

Record Num.	Name	Comment
19	proc_info_flags	XXXXXXXXXn
60	x_cen	X centroid (pixel unit)
61	y_cen	Y centroid (pixel unit)
62	x_epsilon	X error (pixel unit)
63	y_epsilon	Y error (pixel unit)
64	chi_squared	sigma 0 centroider error fit
65	x_sigma	sigma on X direction
66	y_sigma	sigma on Y direction (only for elliptical centroider)
67	xy_sigma	correlation coefficent (only for elliptical centroider)
68	cen_iterations	Iteration number or flag (0,-1,-2,-3)
69	cen_local_sky	Local sky recomputed from the centroider fit using a slating plane
70	cen_int_density	Integrated density recomputed from the fit

Calling Sequence :

CENTROIDER_MULTI imagefile

[/XRANGE=(lx,ux)]

{default entire plate}

[/YRANGE=(lx,ux)]

{default entire plate}

[/CENT_TYPE=a] Type of centroider

{def=CIRCULAR}

CIRCULAR ----> Circular Gaussian + slanting plane as local background

ELLIPTICAL --> Elliptical Gaussian + slating plane as local background

[/NUM_IT_MAX=n] Max. number of iterations

{default = 50}

[/ERR_TOLL=t.] Max. differences on the parameters computed at (step i+1 - step i) multiplied for 1000

{default 0.001}

[/NO_ERR_FILE] Don't write the oop.object_number, oop.cih_id and flag centroider for the object where the centroider fails.

{default write on the file ****.centr_error with this format='(2x,i8,2x,i8,2x,i2)' oop.object_number,oop.cih_id,centroider_flag}

[/VERBOSE]

[/DEBUG] Debug mode

Availability :

GSSS AXP - yes
GSSS VAX - yes
PIXELS - no

History/Author :

Version/Date	Developer	Inst.	Comment
02-Oct-1997	Andrea Zacchei	CRA/OATo	Original Implementation

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