Pipeline Data Registration

From Tauwiki

[edit] The steps in the Pipeline Data Registration module are:

1. Get level_1f file containing x, y and RA,DEC values from UVS_calc_radec module.

2. Take 10 frames and convert RA, DEC to x, y

3. Create image and find point sources

4. Select 3 bright points

(steps 2 to 4 are done for second set)

5. Convert x, y to RA,DEC

6. Pass RA,DEC as reference to CD creation program. Get x, y from point sources of new set. Create CD.

7. Pass new CD to program that creates x, y (for reference set).

8. Convert RA, DEC to new x, y using created CD. The image will be created using new x,y.

Loop repeats.

[edit] Testing - Status :

I.Conversion from RA,DEC to x,y:

WCStransform(used previoulsy) is giving wrong result.This method was taking CDELT and CROTA (which is the average of CROTA1 and CROTA2 if the difference is < 2 degrees). The CROTA1 and CROTA2 are not equal. If the difference is <2, IDL suggests using average. But we found this created CD that is not exact. So we replaced WCStansform by ad2xy and xy2ad from idl which use CD elements. This is working properly when compared with IDL.

WCStransform is calling CelestialTransform internally which is doing right. So we used this CelestialTransform internally when implimented ad2xy and xy2ad equivalent to wcssph2xy and wcsxy2sph. Now registration program will take previous CD or 8.8E-4 (ref.CD) if the point sources are not conistent, or CD created are outside range.

Test Report: Used LATPOLE =0 and LONGPOLE=180. Is it correct?. Results: CD = -6.223917E-4, 5.9604645E-7, 1.1920929E-7, 8.7851286E-4,

RA_CENT = 1.0, DEC_CENT = 45.0

ra = 0.7178767, dec = 45.0; [WCS]: xnew = 965.260, ynew = 511.819; [IDL]: 832.524, 512.1778.

ra = 0.72666556, dec = 45.006; [WCS]: xnew = 951.145, ynew = 518.829; [IDL]: 822.507, 519.16.

ra = 1.0, dec = 45.399; [WCS]: xnew = 512.359, ynew = 966.20; [IDL]: 512.087, 966.203.

But with the reference CD, 0.00088, the result is right for WCStransform, beacuse CD is not affecting.

II. RA, DEC from Spacecraft will not be precise:

Precision of RA is 0.1 degree. Now first CRVAL is obtained from header and subsequent values are obtained by incrementing based on scanrate (fixed) instead of getting from header. This can be calculated from shift in bright points. This has been coded, but not included (commented out). Cross-correlation method can also be used to find shifts. This is to be implemented while comparing with standard catalog. So that can be included here also if needed.

(One approach for loss of precision problem is use x, y without using the converted RA, DEC. But then we need other code for alignment, and also RA, DEC have to be calculated.)

III Point Source Extractor Parameter Values:

S of the S,W, and Z values is independent and given a random nature. This causes spread of points which results in extra random points. So we removed this random nature. Then the smear flag should be true for the point source extractor to detect points. The kappa sigma value (k value) is the deviation from the median pixel value. So the pixel values more than median + k will be considered for bright source detection. This depends on the background. The default value of 2.0 is fine if there are no much bad pixel values. The k value can be made larger if the detected sources are not real ones. But we use it for alignment only and not for recording sources. So this value is less important than smear flag.