Evaluating Polar Alignment with TPoint

After accurately mapping a dozen or more points use the button More Terms found on the left/center of the Fit Data dialog (highlighted above) to access the Suggest New Terms the Terms Wizard.

In order to achieve good all sky pointing as well as obtaining accurate polar alignment information reported by TPoint you must first fix as many pointing issues with the system as you can to obtain an accurate assessment of polar miss alignment. If not the overall pointing and polar alignment information will be compromised. The "Suggest New Terms" button found on the "More Terms" dialog is a very powerful and very easy to use tool.

By adding several additional "proper" terms (say 4 to 8) you will almost always see an appreciable improvement in RMS pointing and the TPoint values reported for polar alignment will also be accurate and can then be trusted. But not before! The following demonstrates exactly this. By adding additional "proper" terms is key to using TPoint effectively to determine polar alignment! And using only the 6 basic EQ terms you cannot fully trust the polar alignment information.

You will see from the following data provided why one can often "chase" their own tail when trying to make the polar alignment better using the information presented by TPoint.

NOTE:  With the Paramount ME one huge advantage to the mount design is you can make very precise and accurate adjustments to both Altitude and Azimuth quite easily. And most importantly,  after you have made an adjustment the amount TPoint has reported, the Paramount ME will not randomly move in either RA or DEC when tightening the knobs to hold it in the new position. For those without a Paramount ME use calibrated live video!

Details on how to make the adjustments <--- Click here

The Terms Wizard!

Software Bisque has over the years found that it is difficult/confusing at best for first time users of TPoint to figure out what terms to use on their own with no prior experience. Since this is no simple task this is expected and completely understandable. Don't worry! There are far too many variables to "play" musical terms. To address this TPoint for Windows has the ability to mathematically figure out which terms to use by performing a "best fit" so the user need not be overly concerned with the process of evaluating the model to figure out what terms apply and those that do not. This is a very good starting place

The Add Harmonic Terms dialog accessed by clicking "Suggest Terms" on the More Terms dialog is a great way to get started. Granted this may not always yield the very best set of terms, i.e. as needed when employing ProTrack by enabling tracking corrections in both RA and DEC based on the TPoint model but it is a very good starting point and highly recommended for TPoint beginner's.

Click Suggest Terms on the More Terms dialog to access the Add Harmonic Terms dialog shown below.

Add New Suggested Terms
 
Before assessing Polar Alignment information

Add Harmonic Terms

Let TPoint do the work!

Press the Start button highlighted above. Note on slower PC's this can take some time so be patient! After pressing the start button a new term has been found and applied. See Below! The RMS Before the term was 71.09 arcseconds and is now a lower 66.58 arcseconds. On the following dialog the values have been highlighted as New RMS and Prior RMS.

Add Harmonic Terms

(The Terms Wizard)

After the first term has been added click on the Start button a second time. Please refer to the TPoint manual for more. Or visit the following web site,

Again note the new RMS and PSD values. Was 42.85 arcseconds and is now 39.73.

After adding a new term

Note the new lower RMS value on the left

Keep adding new terms (Start | Add to Model) until the RMS value no longer decreases appreciably, the law of diminishing returns. Normally using

  and then

adding 6 to 12 new terms using this method should be plenty to achieve good RMS pointing, usually well under 1 arcminute RMS!

Finally result 20.24 arcseconds RMS!

Keep in mind that "fewer" terms is always best. And using improper terms can cause conflicts and actually make things worse! Do not add a term if you are unsure. Again, it is best to use the magic of the "Terms Wizard" - More Terms | Suggest New Terms if you are unsure as to which terms apply or if you are a new TPoint user.

Example Polar Alignment Information Before and after adding terms

TPoint reporting Polar alignment information before adding any new terms.

Az = 0.5 arcminutes / Alt = +2.1 arcminutes

Note the amount of polar alignment error reported
high Sigma values - Don't TRUST!

Now see below the more accurate TPoint Polar Alignment information after adding additional terms using "Suggested New Terms".

Az = 3.5 arcminutes / Alt = +1.3 arcminutes

NOTE LOWER SIGMA VALUES!
A completely different story and the results can be trusted!

Note the difference in the reported Polar Alignment information before and after adding proper terms by using the Terms wizard. The first report leads one to believe that the polar alignment is off by several arcminutes in both axis.

NOTE: If you do not any additional terms before looking at the  Polar Alignment Information reported by TPoint | Model |  Polar Alignment Information the reported values are not technically correct and therefore they cannot be fully trusted.