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| howto:astrometry [2009/04/30 22:06] – pkubanek | howto:astrometry [2009/11/29 09:17] – wildi |
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| ====== Image astrometry parameters ====== | ====== Image astrometry parameters ====== |
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| RTS2 is able to support on-line astrometry, with corrections being fed back to the telescope as correction parametes, thus significantly improving the telescope pointing. Following is list of parameters which affect astrometry, and a guide how to set them up. | RTS2 is able to support on-line astrometry, with corrections being fed back to the telescope as correction parameters, thus significantly improving the telescope pointing. Following is list of parameters which affect astrometry, and a guide how to set them up. |
| | For rts2-camd-dummy and rts2-camd-fli specify all parameters in file ///etc/rts2/devices//. |
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| * **XPLATE** and **YPLATE** - size of pixel in arcseconds in X and Y direction. This is specified by //--plate <x>:<y>// parameter, passed to camera daemon (preferably in ///etc/rts2/devices// file). If you have 0.3 arcsec in X and 0.2 arcsec in Y (=non-square pixel size), you specify //--plate// 0.3:0.2 (//not supported on the astrometry side, though :-|//). **XPLATE** and **YPLATE** are normal variables, displayed in **rts2-mon**. Camera daemon change them when you change binning - their change should be immediately visible. You can also change them directly in **rts2-mon** - but those changes will not be recorded (if you restart camera daemon, they will be lost). **XPLATE** and **YPLATE** are present only when //--plate// parameter is included among camera daemon parameters. Precision needed for the astrometry to run smoothly is relatively high (~5%), so it is best to get the values from dry runs of the astrometric routine. Crude estimate may be done in various ways, pixel_size[arcsec]=pixel_size[um]*206.265/focal_length[mm] being a quite useful formula. A good way is also getting some known field (with a nebula or a small galaxy) and trial-error with the astrometric routine. | * **XPLATE** and **YPLATE** - size of pixel in arcseconds in X and Y direction. This is specified by //--plate <x>:<y>// parameter, passed to camera daemon (preferably in ///etc/rts2/devices// file). If you have 0.3 arcsec in X and 0.2 arcsec in Y (=non-square pixel size), you specify //--plate// 0.3:0.2 (//not supported on the astrometry side, though :-|//). **XPLATE** and **YPLATE** are normal variables, displayed in **rts2-mon**. Camera daemon change them when you change binning - their change should be immediately visible. You can also change them directly in **rts2-mon** - but those changes will not be recorded (if you restart camera daemon, they will be lost). **XPLATE** and **YPLATE** are present only when //--plate// parameter is included among camera daemon parameters. Precision needed for the astrometry to run smoothly is relatively high (~5%), so it is best to get the values from dry runs of the astrometric routine. Crude estimate may be done in various ways, pixel_size[arcsec]=pixel_size[um]*206.265/focal_length[mm] being a quite useful formula. A good way is also getting some known field (with a nebula or a small galaxy) and trial-error with the astrometric routine. |
