Several values can be entered on the Setup window for the ServoCAT ASCOM driver. These values include:
Serial Port (Required)
ArgoNavis is set to do refraction correction (Recommended)
Site Longitude (Optional)
A proper serial port setting is critical in order to establish proper communication between the ASCOM driver and the ServoCAT hardware.
The ArgoNavis default setting is to calculate refraction corrections, and to apply them to RA /Dec values before sending this information to the ServoCAT. If your ArgoNavis is set to this default setting, then indicate this with a check mark in the box on this screen. If your planetarium software also calculates refraction correction, you may wish to turn off this setting in the ArgoNavis and remove the check mark on this setup screen. This may avoid a situation where the refraction correction is doubly corrected.
The ServoCAT ASCOM driver only uses site longitude if the planetarium software queries the driver for Sidereal time. The value you enter here is not read from nor written to the ServoCAT or the ArgoNavis. Likewise, sidereal time is neither read from nor written to the ServoCAT or the ArgoNavis. If you find that your planetarium software is using an incorrect value for Sidereal time, and you have already set the proper site location in your planetarium software, it is possible that the planetarium software is ignoring these settings, and trying to get the value from the ServoCAT ASCOM driver. If this is the case, then you need to make sure that the proper site longitude is set here in the driver.
When entering your site longitude on the setup screen, please convert the longitude to decimal degrees. To do this, divide the value of longitude in seconds by 60 then add this to the value of your site longitude in minutes. Next divide the new value of the longitude in minutes by 60 and add it to the longitude in degrees. If your longitude is west (true for North America), indicate this by prefacing your decimal longitude with a negative sign, if your longitude is east, just enter it as-is. Valid values for longitude range from -180 to 180 degrees. If you do not want to worry about this setting, then leave it at 0. Note: a value of 0 will be used to indicate that no longitude has been given, so, if you are precisely at longitude 0, you will need to fudge it a bit to something like 0.00001 !
Decimal Degrees = Longitude degrees + Longitude minutes/60 + Longitude seconds/3600
If Longitude is West, then Decimal Degrees = - Decimal degrees
Example: 105 degrees 56 minutes 24 seconds West = -105.94
Please see the file ServoCAT ReadMe.htm for more details about the ASCOM ServoCAT Driver including a discussion of coordinate reference systems and refraction correction.