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howto:astrometry [2009/11/29 09:17]
wildi
howto:astrometry [2009/11/29 00:00] (current)
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 ====== Image astrometry parameters ====== ====== Image astrometry parameters ======
  
-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. +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. These parameters are arguments to the rts2-camd-* device drivers ​and are best set in the file  ///​etc/​rts2/​devices//​.
-For rts2-camd-dummy and rts2-camd-fli specify all parameters ​in file ///​etc/​rts2/​devices//​.+
  
-  ​* **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. 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. ​
  
   * **FLIP** - that depends on readout direction and used optics. Can be also regarded as indication of negative **XPLATE** - e.g. arcseconds rose in different direction along X axis then is common. It is 1 for most cameras, the only exception so far is Andor, which have 0 flip for EM channel and 1 for non-EM channel. This is set in the driver and unless you put extra mirror in optics, should be correct. If needed, you can set flip with //--flip// parameter passed to camera daemon. Again, **FLIP** is visible in **rts2-mon**,​ and can be changed from **rts2-mon**.   * **FLIP** - that depends on readout direction and used optics. Can be also regarded as indication of negative **XPLATE** - e.g. arcseconds rose in different direction along X axis then is common. It is 1 for most cameras, the only exception so far is Andor, which have 0 flip for EM channel and 1 for non-EM channel. This is set in the driver and unless you put extra mirror in optics, should be correct. If needed, you can set flip with //--flip// parameter passed to camera daemon. Again, **FLIP** is visible in **rts2-mon**,​ and can be changed from **rts2-mon**.
howto/astrometry.txt · Last modified: 2009/11/29 00:00 (external edit)