[vsnet-chat 813] Re: vsnet charts

[Taichi Kato <tkato>]

(Re: vsnet-chat 810)

Fraser Farrell wrote:

> The ability to display VSNET charts at different scales would go a long
> way to reducing the crowding problem.  Not just with <20th mag USNO
> stars, but with (for example) clusters and rich starfields generally.
> I see real advantages in having two (or more) VSNET charts - CHTs - at
> different scales for some objects:

   Your suggested way seems to be feasible.  As a matter of fact, we have
already had experiences of dealing with charts different scales, especially
when making charts from Skiff's wide-field photometry.  The only omission
is the explicit column for the field scale.

> As for the other problem of showing legible labels on VSNET charts; I
> say this is a problem for the display software - not the CHT author.
> The CHT author cannot know the capabilities of the system which may be
> used to show or print the CHT.  This includes such things as screen
> fonts, colours, resolution and other issues that affect legibility.

   For those interested, our chart viewer (sorry on our domestic PCs, not
on Windows nor DOS/V) has a default function to avoid overlapping labels.
This routine has been provided from Takenaka-san (probably some of readers
remember his and Granslo's works on Nova Cas compliations).  This function
searches the "blank area" (by checking pixels) nearest and most appropriately
situated to the plotted star.  GIF charts generated by this program is
often linked from the relevant VSNET Web pages.  This strategy looks quite
similar to what Fraser has written:

> I wrote a rudimentary intelligence into the label display, which greatly
> improves legibility. VSSPlot searches several locations around the star,
> looking for the "emptiest space" to put the label.  The definition of
> "emptiest" being "minimum number of non-black pixels".  This checking
> does slow down CHT displaying, but the result is a lot better than a
> simple always-put-the-label-beside-the-star.

   We have another chart displaying tool (also on our domestic PCs ..),
which automatically adjust limiting magnitudes when changing the field
size.  Automatically limiting, or labelling on certain specified number of
brightest stars may be other feasible options.

Regards,
Taichi Kato

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp