GPS and Goto Accuracy

[BarnMiguel]

Hi,

I've been using a GPS coordinate converter app (Coordinate Tools) which gave me 1 50' W for Oxford but I noticed on Google maps the value was actually 1 10' W. Goto accuracy was very good and I always got the object in the FOV but last night I used the correct coordinates and the Goto was terrible even after a few attempts and a polar realignment (with alignment afterwards). Am I using the correct coordinates? Is the polar realignment on the skywatcher mounts poor? I've used EQMod to find the position of polaris with good results but have yet to try with the new coordinates.

I've never been able to achieve >30s exposures which I guess I'm stuck with because of the equipment I have. I will be able to guide, I tried it last night but calibration was about to finish but my laptop ran out of power! I want to try and get at least good polar alignment but just can't seem to achieve it. Is it possible to get close to 1min exposures with a 200PDS and EQ5 Pro unguided?

Thanks for reading,

Mike

[ronin]

Have you swapped between the corodinates that the gps seems to be giving (degrees and minutes) and what Google supply (Decimal degrees).

Centre of Oxford is -1.25 google, = 1 15'W

The value you give of 1 50'W (-1.8) is out by Fairford, so no where near Oxford, unless you are giving Oxford as the nearest big place.

At this time I am suspecting a misread = is it 1 50' or 1 5' and/or you have not converted from degrees and minutes to decimal values for degrees. Pretty easy for the last one as minutes never get above 60 so "look" right half the time.

[BarnMiguel]

I think the app I was using incorrectly converts decimal to degrees/minutes as the decimal value was -1.17 for the dark(er) site I got to which was converted to 1 50' W. Google does give the gps in decimal but I've been using the converted value checked by putting the degrees/minutes into google maps which gives the correct location as -1.17 for 1 10' W which is where i realised the converted app was wrong.

It just seems strange that my goto and polar realignment seemed so much more straight forward and accurate when I used 1 50' W which like you say is quite a bit west of Oxford.

[ronin]

Agreed it makes little sense, but from experience several bits make little sense on some goto's. More then once to change a piece of data I have found it easier to clear everything. Sometimes the only way I could change one bit of data was to clear it all and start again.

I think that part of the problem is these came out 10-12 years ago and computing power was limited, we are now used to much more. Lets face it no qwerty keyboard, no mouse, no touch screen. All goto scope interfaces are now quite antique. Where is the Android app for me to run one from a Nexus7 or iPad ?

If you have a custom location in the scope I would half think of deleting it and re-entering it as if new.

Looking at it, it almost reads as if the numbers are converted the wrong way.

Oxford centre is -1.25, if you were a little West, Botley, then very close to -1.30.

If 1.30 is entered as decimal but taken as 1 30' then this converts to 1.5, 1.5 looks a lot like 1 50'

It is almost as if you are inputting in decimal and the tool is thinking they are degree+minutes, and the conversion is the wrong way round.

Out of interest for Latitude you do have 51.75 = 51 45N ? More or less.

[malc-c]

Pop down to maplin and pick up a USB GPS dongle for £30 - it will give you the exact position and altitude that is good enough for setting up the handset

[BarnMiguel]

I use my mobile for gps coordinates so I have the correct latitude (51 44') I was just confused as to why the goto accuracy was so poor when putting the correct longitude compared to being very good when using the wrong longitude.

I will do a full reset on the mount for when I try it next as that seems a reasonable cause. Thanks for the suggestion.

[mallorcasaint]

One of the best maps to ue is itouchmap.com which will give you your coordinates in Degrees, Mins and seconds ( the correct format ) from your address.