On 06/11/2013 12:51 PM, pastorgalactico wrote:

> Hello;
>
> Why in guide 9.0 to represent a star out up to 3 representations of the same star at nearby positions, for example;
>
> Polaris
> Out 4UC897-000295 RA: 2h31m52. +89 15 '50,632 "
>
> Polar TYC 4628 237 1 02 31 47.08 +89 15 50.9
>
> 02h31m47.0780s A2_1725_00116912 +89 15 '50,890 "
>
> This happens if we have to leave the catalog represented ucac4 and USNOA2 and high zoom.
> Is there any way to solve this.?

Not at present, no.

This is a problem of (_very_) long standing. I was able to address it with Guide's
"built-in" catalogs by doing a lot of pre-processing to flag which stars appeared in
other catalogs. I don't have such a system for added catalogs such as UCAC-4 and A2.0.

I don't think it's impossible to do this. Essentially, Guide would need to be
able to say: "First, draw Tycho-2 stars. Next, when drawing each UCAC-4 star,
check to see if is within (say) .5 arcseconds of a Tycho-2 star that has already
been drawn. If so, don't draw it. Next, draw the A2.0 stars; when doing so,
check to see if the star is within (say) two arcseconds of a UCAC or Tycho-2 star."

The tolerances would have to be flexible, and would vary from one dataset to the
next. A2.0 is nowhere near as exact as UCAC-4; if the positions are two arcseconds
apart, it's probably still a duplicate object. But a 2" separation between Tycho-2
and UCAC-4 may be "real".

A smarter algorithm would probably notice if multiple stars were within the
distance of a previously-catalogued star. Suppose you've got a mag 10.5 Tycho-2
star, and UCAC-4 shows a mag 10.5 star within 0.1" and a mag 12.3 star 1.2"
away. In this case, I'd bet that UCAC-4 has successfully split a close double
that Tycho-2 missed.

I long considered this to be a nice idea, but unfeasible because of the
processing power required. (Which is why I basically did the same thing for
Guide's built-in datasets, but did it ahead of time, processing the data over
a few nights.) I have to admit that, with current processors, it might be
becoming feasible to do this in real time.

The current method _does_ mean that you can get information from each of the
catalogs. But of course, that just means it should be possible to shut off the
scheme I've just described (perhaps by temporarily setting all of those distances
to zero arcseconds.)

-- Bill