Pointing Model Tab

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Pointing Model Tab

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Operation

Enable Pointing Correction: When checked this enables APCC's pointing correction logic.

Enable Tracking Correction: When checked this enables APCC's tracking rate correction logic.

Note:  You must have a model loaded in order to enable pointing or tracking correction.  See the section on APPM for further details in preparing a model.

Model..:  Opens the pointing model window. In this window you can view and change the pointing model.

APPM: Runs the Astro-Physics Point Mapper (APPM) utility, which is included with APCC Pro. APPM is what is used to create pointing models used for pointing and tracking rate correction.

Temp: If no supported temperature sensor is present then in this field you can enter the temperature in Celsius. Temperature is used in the refraction calculations. At this time, devices with ASCOM ObservingConditions  the THUM (Temperature Humidity USB Monitor) sensor is supported.

PointinModel-Operation-NoTHUMAttached  

If a supported temperature sensor (THUM) is attached to the computer then the temperature from the sensor will not be editable. The temperature field will change color to indicate this. Hovering the mouse over the temperature field will show humidity and dew point. APCC will read the THUM device throughout your session when connected.

NOTE: When using a THUM temperature/humidity sensor do not install or run the THUM service. Only one application at a time can connect to the THUM, per the design of this device. So, if the THUM service is running APCC cannot read data from the THUM (nor can it connect to the THUM service app)..

 

PointinModel-Operation-WithTHUMAttached

 

A Note about Temperature:

Even a modest temperature change can make a measurable impact on refraction. APPM will record the temperature at each plate solve for later use. Even though there may not be a significant change in temperature on any given night, there may be a significant change from the night the Pointing Model was created. APPM and APCC can account for the difference in temperature between nights to provide the greatest pointing and tracking rate correction accuracy possible.

For the purposes of refraction the best air temp would be that measured at least 10-15 feet above the ground.

For the purpose of calculating focus point the temperature of the focuser/OTA is best used. Your focusing software will account for these temperature changes. It is not a function of APCC.

Pressure: Here you can enter the approximate atmospheric pressure. This is used for refraction calculations. The atmospheric pressure varies based on two principal factors:  the weather, and your altitude above sea level.  Note that this differs from typical weather forecast "barometric pressure" which is the atmospheric pressure normalized to sea level.  Do not use barometric pressure values.   Light is being refracted by the actual air mass above your telescope, not the equivalent normalized sea-level air mass.   As an example: mean sea-level atmospheric pressure = average barometric pressure = 1013 mB.  The Astro-Physics observatory is at an altitude of about 228 meters above sea level - none too high.  The sea-level value of 1013 mB is equivalent to about 987 mB of actual atmospheric pressure here at AP.  At a remote observatory in Chile at an altitude of 2295 meters, that same sea-level value is equivalent to about 770 mB.

For any given altitude, the atmospheric pressure will have a certain range of variability that can be expected.   Within the range at your observing spot's altitude, you will find that higher pressure corresponds with nights where it is clear enough to actually use the telescope, and lower pressure corresponds with cloudy or even stormy weather.   When manually entering a value here, enter one that corresponds with the high pressure value for your altitude that you would be likely to find on a good clear night.    In a future release, APCC will add support for weather station software so that this value can be kept updated in real time.

Pointing Correction Status

If Enable Pointing Correction is checked this group box shows the RA and Declination adjustments that are currently applied to the mount. RA is shown in RA minutes and seconds - Declination is shown in arc-minutes and seconds. They are updated approximately once per second.

Pnt_Mod_Pnt_Cor_Stat_2016-1209

Under certain circumstances the boxes will read with other values:

Not Tracking

The mount is not tracking.

Parked

The mount is parked.

Slewing

The mount is slewing.

Near Pole

Dec > 80 or Dec <= -80 degrees

Tracking Correction Status

If Enable Tracking Correction is checked this group box shows the RA and Declination rate adjustments, in RA-seconds/hour and arc-seconds/hour respectively, that are currently applied to the mount. They are updated approximately once per second.

Pnt_Mod_Trk_Cor_Stat_2016-1209

Under certain circumstances the boxes will read with other values:

Not Tracking

The mount is not tracking.

Parked

The mount is parked.

Slewing

The mount is slewing.

Near Pole

Dec > 80 or Dec <= -80 degrees

Pointing Model

This group box shows some of the major terms extracted from the pointing model. It is not all-inclusive of all terms and properties used in the pointing model. The pointing model will also take into account refraction and interpolation of residual pointing terms to provide greater accuracy than just these major terms. With time refinements and additional terms may be made visible.

Point-Mod-Grp-Box-2014-0724

NOTE: All coordinates are in JNOW. In APPM plate solves involving catalogs with J2000.0 coordinates are precessed to JNOW for the purpose of creating pointing models.

This said, you may find these terms useful for evaluating certain mechanical aspects of your setup. There are two columns for the terms. The left column contains the East model's term values. The right column contains the West model's term values. HOWEVER, do not treat these values as absolute.  APCC's sophisticated modeling uses a "best fit" approach.  The values may tell you whether you have a problem with orthogonality or with your polar alignment, but the exact values from the model are not appropriate guides for making precise polar alignment adjustments, or for shimming an OTA.

Offset Error - Hour Angle

This is the index error in the Right Ascension axis. For instance in a perfect telescope system if the scope is pointing at exactly RA=10h 00m 00s but the telescope coordinates show RA=10h 02m 04s, then the error is 00h 02m 04s. This type of error can usually be fixed by syncing to a known RA/Dec coordinate (e.g. via a plate solve).

Offset Error - Declination

This is an index error in declination. For instance in a perfect telescope system if the scope is pointing at exactly Dec=35d 00m 00s but the telescope coordinates show Dec=35h 04m 07s, then the error is 00h 04m 07s. This type of error can usually be fixed by syncing to a known RA/Dec coordinate (e.g. via a plate solve).

Non-perpendicularity (HA,Dec)

This is the non-perpendicularity between the Declination axis and the Right Ascension axis. There are RA and Dec components to this error but they are both combined in the value shown.

Non-perpendicularity (Dec,OTA)

This is the non-perpendicularity between the Declination axis and the OTA. There are RA and Dec components to this error but they are both combined in the value shown.

Polar Axis Elevation

This is the polar alignment error in Altitude. A positive value means the axis is pointing higher than the true pole. Refraction is not included.

Polar Axis Azimuth

This is the polar alignment error in Azimuth. A positive value means the axis is pointing to the West of the pole when facing the pole.

Tube Flexure

This is the amount of flexure in the tube. There are RA and Dec components to the flexure but the value shown combines both.

Flexure in Cantilever Axis

A cantilevered beam is one that is anchored at one end only. In the case of the telescope it is the flexure of the RA and Dec axes caused by gravity. There are RA and Dec components to the flexure but the value shown combines both.