Using T-Point and Automapper II to confirm your Alignment

  1. Read the instructions for Tpoint and Automapper II.

  2. Download the USNOSA database and add it to TheSky. Watch out its 633 MB in size and contains 50,000,000 stars. This is needed to give TheSky and CCDSoft a good database for Astrometry solutions.

  3. Make sure you can Automap points using Automapper II, CCDSoft, Tpoint and The Sky. Make sure you set the slew speed on Autostar II to the maximum otherwise it will error. I also remember setting a 8 second delay after the slew with Automapper II.

  4. Get familiar with Tpoint and learn how to add terms and interpreting the data. Read the guides that came with Automapper II and Tpoint. Otherwise email me and I will help you.

  5. Setup an Automapper II run and map 150-250 points with Tpoint anything less will provide sub-accurate results (this will take a few hours).

  6. With respects to Tpoint:

    1. Set the pressure to 0 (if using a LX200Gps).

      Observing parameters window in Tpoint
    2. Reject any outliers. Points that have mapped in error. The dots in the scatter graph will be 500+ arc-seconds out and all by itself.

      What outliers look like in Tpoint
    3. Once you have the data, add terms so the PSD reduces never add a term that increases this value, add one term at a time.

      Adding terms in Tpoint Reduced PSD value in Tpoint
    4. Stay away from the suggested harmonic terms. In rare cases I might add one as long as it reduces the PSD by a good amount and doesn’t increase the sigma of the other terms.

      Suggested harmonic terms Good harmonic terms
    5. As you add terms the sigma on each term should get smaller not larger otherwise reject it.

      Highlighted sigma information
    6. Reject a term if the value number isn’t at least three times larger then the sigma value (disregard positive or negative numbers). Don’t reject ME or MA terms.

      List of terms that match our criteria
    7. Once this is done you can evaluate your polar alignment with confidence. The lower the polar alignment sigma the better its accuracy.

      Successful polar alignment

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