Re: [guide-user] Re: colors in horizon.dat

Bill Gray Feb 2, 2018

Hi Rudi, Bernd,

First off: Rudi, Guide does have a built-in 'horizon.dat' and
'objects.dat'. You won't see the files in the Guide folder, though,
until _after_ you have turned on horizon objects and they've been
displayed. (And they don't get displayed unless your viewpoint is
on the surface of the earth; the moon and Mars have their own horizon
files, and the geocenter has no horizon file.)

You're right about the colors for circles. (The comments you found
are for TDF files; none of those coloring tricks work in the horizon
drawing code.)

In 'horizons.dat' and 'objects.dat', circle colors can only be set
as index values from 0 to 15. Colors for filled areas and polylines
can be set as red/green/blue decimal values (which is no longer a
common way of specifying colors, and hasn't been for some years now.)

I've posted a fix for this. Download

(about 620 KBytes) and unZIP it there. It'll overwrite some existing
files, updating both Guide and the horizon and object files.

With this, colors for 'f' (filled objects), 'c' (circles), and 'l'
(polylines) can be specified as six-character hexadecimal codes.
'996633' should come out as a light brown.

You'll also see a band at 60 degrees above the horizon (roughly).
This _could_, in theory, have been done by adding

c 996633
0 90 30

("draw a circle with RGB color #996633, centered on azimuth 0,
altitude 90, with a radius of 30 degrees"). However, projection
effects will make that not all that close to showing an altitude
of 60 degrees. The circle drawing really only works for circles
less than about ten degrees across.

So instead, I put this line into 'horizons.dat' :

i alt_mark 0 60 1

If you look in 'objects.dat', you'll see that an 'alt_mark' consists
of six 60-degree segments, each of which draws six ten-degree pieces.
Each of those pieces consists of two triangles, which make a 10x10
degree square. (Well, ten degrees wide in azimuth... at an altitude
of sixty degrees, that's compressed by a factor of two.)

Also, note that for the purposes of these files, an altitude of
zero means "at your visible horizon", which is affected by refraction
and your height above sea level. You may have to change the '60'
in the above line to get the altitude marker where you really want it.

And a final comment: Bernd, you mentioned in a private e-mail
that you have at least ten different horizon files for different places,
and would like a way to swap them around. Not to raise your hopes too
much, but it occurs to me that the most sensible way of doing so would
be to have lines in 'horizon.dat' that would say

L -69.9 +44.01 bowdoinh.txt bhm_objs.txt

...i.e., "if you are at longitude 69.9 West, latitude 44.01 North,
stop processing this horizons.dat file; switch instead to bowdoinh.txt,
getting your objects from bhm_objs.txt'."

You could have a series of such lines -- at least ten, in your
case. If Guide read through all ten and effectively said, "No,
that's not where we are", it would continue and just display the
default horizon.

-- Bill

On 2018-02-02 06:51, chasseurdesgalaxies@... [guide-user] wrote:
> Hi Bernd,
> I tried to reproduce your problem, because I am also interested to have a "fixed" 60° line around the zenith. (I have a "workaround" but it moves position, when i move the map from the zenith position. I will come back on this).
> BUT, I don't even have ahorizon.dat file in my Guide folder?? (Despite the fact that I have switched on thea horizon line and can switch it off and change color).
> Found this (first link) and installed the horizon.dat file : ,
> ... but it doesn't work for me either !??
> Here, , somewhere in the middle of the text under "Defining your own custom .TDF symbols" it is said as follows:
> "It used to be that color was always set with lowercase 'c' followed by a number from 0 to 15. That was a legacy of the old DOS days, in which objects could only have one of a palette of sixteen colors. This is still available for purposes of keeping Guide backward-compatible, but Guide 8.0 can set "full colors" with an uppercase 'C'.
> The easy way to set this is to create your symbol with either a 'c' or 'C'-type color selected basically at random. Then fire up Guide, click on an object in the dataset, and then on "Display", and then on the color button. Select a new color and click OK, and the symbol will be rewritten to use the new color".
> Sorry, I can't help you further. (What is strange is, that the last word in the last quoted link is saying "useless" ??)
> What I am doing is creating an aperture cercle (in "Settings \ Tips, Grids, ect") of 60° (in my case). By setting the cercle to 120 ° (you need to add the degrees sign (°) behind the number, I have a cercle of 30° above the horizon). And with this cercle you can change color as you want.
> But, as I said, there is the drawback that, if you move the map from the exact zenith position, the cercle follows and does not stay around the zenith position.
> Rudi