Thanks Bill - this is exactly what I wanted to do. I knew that Guide could
produce useful projections but I could not find exactly the combination to do
it.

BTW because Guide has many facilities that I have never used, I was unable to
understand Konstantin's suggestion. My thanks to him as well for taking the
time.

thanks and regards

Lawrence

>Re: Sky projections
> Posted by: "Bill J Gray" pluto@... feliks314159
> Date: Sat Sep 8, 2007 1:10 pm ((PDT))
>
>Hi Lawrence,
>
> Short answer: go to the Inversion dialog, and select "Zenith Up". Keep the
>simple cylindrical projection (or at least some sort of cylindrical projection).
>
> Longer answer, explaining why the above works:
>
> As you found, just selecting a simple cylindrical grid (or any other cylindrical
>projection), and doing nothing else, gets you a projection in which following a
>vertical grid line shows changing azimuth, but constant right ascension. Following
>a horizontal one gets you a constant declination. This is similar to, say, a
>Mercator projection of the earth, where meridians of longitude are vertical lines
>on the map and parallels of latitude run horizontally. The North and South poles
>become lines at the top of the map... which, for star charts, means the areas
>around Polaris and Octans. (Which is why you don't _usually_ use a cylindrical
>projection for star charts.)
>
> Switch to "Zenith Up", and Guide stops projecting RA/decs and starts projecting
>alt/azimuths. Suddenly, it's the lines of constant azimuth that project as vertical
>lines and the lines of constant altitude that become horizontal lines on the chart.
>And instead of the north and south celestial poles getting horribly distorted, it's
>the areas around the zenith and nadir that look ugly.
>
> Actually, as Konstantin suggests, you could make a user-defined "horizon" that
>shows what you're looking for. As you may have seen, you can go into Display...
>Backgrounds, turn on "Horizon Objects", and get a slew of objects (trees,
>mountains, houses, cars, streetlights, etc.) shown around your horizon.
>If you edit the files 'horizon.dat' and 'objects.dat' in your Guide folder,
>you'll see that you can modify these. Most people do so just to alter the
>horizon to show what's blocked at their site. A few people have added circles
>above a particular declination or altitude, to show the area they can't image
>because of their equatorial mount or "Dobson Hole" situation. But you could,
>in theory at least, make a box that shows your observatory shutter.
>
> Dunno if I'd recommend this, though, because (unlike the objects around
>your horizon) your shutter moves from time to time. I didn't really have that
>in mind when I put the horizon system together!
>
>-- Bill