SharpCap Forums

Hello, About a mile from my house, I have a radio tower with a small cross shaped structure at the top which I use for focusing, etc. What I would like to do is set up a sequence to slew my telescope to the tower and focus on the cross. I have a Skywatcher EQ-G mount. I can't get past the first step, however. When I try to slew the mount in the sequencer, I get the error shown. Any ideas as to what might be causing this and what a solution might be? Thanks, Bill

3:54:37 PM Starting :
3:54:37 PM Starting : Move the mount to Alt=50, Az=50
3:54:37 PM Error : 'CheckDotNetExceptions ASCOM.SkyWatcher.Telescope SlewToAltAzAsync System.Exception: Elevation topocentric can not be derived from the information provided. Are site parameters set? (See Inner Exception for details)' while running step Move the mount to Alt=50, Az=50
3:54:37 PM End : Sequence halted due to error.
3:54:37 PM Finished

Hi,

it looks like you are trying to move to AltAz co-ordinates using an equatorial mount - in order to do that, the mount needs to calculate the correct RA/Dec co-ordinates based on your altitude and azimuth values, since the mount is naturally equatorial. For that calculation to work, the mount software needs to know your latitude, longitude and elevation - I think it's the elevation that is missing. Hopefully there is somewhere in the ASCOM mount setup window to allow you to set this information, as it is info that needs to be configured on the mount ASCOM driver rather than in SharpCap.

cheers,

Robin

Hi Robin,

Thanks for the reply. I had thought of that. I specified the location coordinates and the elevation in the ASCOM telescope profile (see attachment). It did not seem to make any difference. Any other ideas as to how to always slew the scope to fixed position? Your insight is always greatly appreciate!

Best, Bill

Hi,

that wasn't quite what I was expecting you to do - I was expecting you to set the location in the Skywatcher setup window - as shown below
You can see in the background that even though the skywatcher window has my lat/long, it's not stored in the ASCOM profile, so maybe that is the issue.

cheers,

Robin

I looked in the mount profile and the elevation was getting passed correctly so that was not the issue. I did note, however, that if I put in RA DEC coordinates, everything works fine. Only ALT AZ gives me the error. The problem is that I cannot go to a fixed point using RA DEC because the coordinates are always changing.

Hi,

the problem is here that behind the scenes your mount is lying

Internally, SharpCap asks the mount if it can slew to AltAz co-ordinates - if it says yes then it sends the slew command. If the mount says no then SharpCap uses your lat/long to convert AltAz to RADec and asks the mount to slew to the calculated RADec co-ordinates. It all works fine as long as the mounts claims match up with its capabilities.

Can I ask if you are using the most recent skywatcher ASCOM driver? I just had a dig through the code of the driver I have here and I can't see quite how it could produce the error you are seeing, which makes me wonder you might have a different version installed?

cheers,

Robin

I updated the mount's ASCOM driver to the latest version but the problem persists. It still doesn't seem to like the elevation parameter. Any further ideas as to what to do? Thanks

Hi,

is it possible to use the EQASCOM/EQMOD driver with your mount (I think it supports most skywatcher ones). Maybe that is better behaved in this respect?

If you had a mount with an easy-to-adjust altitude setting, you could set the altitude for PA to 90 degrees (as if you were using the mount at the north pole) so that the RA axis points straight up. The you could GOTO RA/Dec co-ordinates, but they would work like azimuth and altitude. However it looks like the EQ-G has the same (rubbish) altitude adjustment as the EQ6, ie set it once and try to never adjust it again

Finally, you can persuade SharpCap to tell you what lat/long the ASCOM mount reports - the easy (ish) way is to do this

1) SharpCap Settings -> Polar Alignment, choose 'Use location from ASCOM mount'. Also enable 'correct for atmospheric refraction'.
2) Open camera
3) tick 'Connected' on the mount (if not already ticked)
4) Select polar alignment tool and move to the 'capture first image' step.

In the second column, it should have a section 'Location and Refraction Correction' which will show the lat/long that SharpCap has retrieved from the mount - if it shows an estimated figure then that means the mount refused to give a lat/long to SharpCap (which would kind of tie in with it not being able to do the AltAz goto). If it shows the correct figures then it's very weird because the ASCOM driver obviously knows the location but is not using it correctly!

cheers,

Robin

Hi Robin,

I tried using the mount with the EQASCOM/EQMOD driver as you suggested, and it seems to work just fine with that set up. I was not aware of the EQASCOM/EQMOD driver so thanks a lot for that suggestion! I guess there must be some sort of bug in the Synscan driver.

Best, Bill

Hi Bill,

yes, I think there is a bug - as best as I could work out the Synscan ASCOM driver knows the lat/long, but isn't using it when trying to convert AltAz to RADec, which then fails with the error you were seeing.

EQMOD/EQASCOM is a bit clunky in some ways, but is very fully featured and is probably used by more people than the Synscan driver.

cheers,

Robin