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How to refine obstructed horizon
#1
Hi all,

I am sort of a newbie and I am trying to make obstructed horizon closer to what I can really see in my restricted observing area.

This is my file:

0 90
30 90
45 90
60 90
100 0
170 0
210 90
225 90
240 90
300 90
330 90
359 90 

Try different ways but gets out of shape.

and below is a picture of what it looks like.
Above the dotted lines is what I can not see.
Straight or curved, anyone can help?

Thanks in advance!


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#2
Firstly, your file is saying that you can only see the sky at all between 100 and 170 degrees azimuth. That is very extreme. Are you certain that is correct?

An example using an Overhead Sky Chart would probably be easier to understand. The sky is more naturally depicted.

I'm not certain how to interpret the dashed lines that you have drawn on your chart. You can't see *above* them? That would be very unusual... and I'm not sure SkyTools can do that. The way it works is that you define a "horizon" above which you can see things. This is for obstructions like houses or trees. If you are trying to define a region below a given altitude in the sky all the way to the horizon, then that isn't going to work, at least not directly. Is your telescope under a roof?
Clear skies,
Greg
Head Dude at Skyhound
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#3
(2021-11-11, 06:15 PM)theskyhound Wrote: Firstly, your file is saying that you can only see the sky at all between 100 and 170 degrees azimuth. That is very extreme. Are you certain that is correct?

An example using an Overhead Sky Chart would probably be easier to understand. The sky is more naturally depicted.

I'm not certain how to interpret the dashed lines that you have drawn on your chart. You can't see *above* them? That would be very unusual... and I'm not sure SkyTools can do that. The way it works is that you define a "horizon" above which you can see things. This is for obstructions like houses or trees. If you are trying to define a region below a given altitude in the sky all the way to the horizon, then that isn't going to work, at least not directly. Is your telescope under a roof?

Thank you
Yes unfortunately I observe from a balcony and that is my limit E to S
And there is the large overhang from the balcony above that prevents me from seeing above the dotted line
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#4
Hmm.... the problem is that the SkyTools feature is designed as a horizon, rather than a window. What isn't obvious is that SkyTools uses the obstructed horizon in all of its calculations. Its not just a line on a chart, so there has to be a clever and very fast algorithm to determine if a position in the sky is visible at any given time. So, its not only that there is no "top" to the horizon feature to make a window, but that its built into the algorithm. I'm not sure how I'd even add that.

I do have an idea, however, that might get you close to a full solution. First, start by defining the visible part of the sky in m ore detail. When you transition, you need to tell it not to interpolate between two widely different azimuths. So instead of:

60 90
100 0
210 90

Use:

60 90
61 0
209 0
210 90

That will make the jump from an altitude of 0 to 90 much more "straight."

The second thing is a trick, and it won't be perfect, but it should help. What type of mount are you using? Is it an alt/az mount, like a Dob? Or is it an EQ mount? If its an Alt/Az mount, you can set the Dobson's hole at the zenith. I'm not exactly sure where your maximum altitude is from your chart, but lets assume its 70 degrees. The radius of a Dobson's hole that extends from the zenith to 70 degrees would be 20 degrees. So you would enter twice that (40 degrees) in the telescope setup for the Dobson's hole.

By putting these two things together you should be able to eliminate most of the sky you can't see. You won't get a straight line across just like your roof, but it will be fairly close.
Clear skies,
Greg
Head Dude at Skyhound
Reply
#5
(2021-11-11, 06:43 PM)theskyhound Wrote: Hmm.... the problem is that the SkyTools feature is designed as a horizon, rather than a window. What isn't obvious is that SkyTools uses the obstructed horizon in all of its calculations.  Its not just a line on a chart, so there has to be a clever and very fast algorithm to determine if a position in the sky is visible at any given time. So, its not only that there is no "top" to the horizon feature to make a window, but that its built into the algorithm. I'm not sure how I'd even add that.

I do have an idea, however, that might get you close to a full solution. First, start by defining the visible part of the sky in m ore detail. When you transition, you need to tell it not to interpolate between two widely different azimuths. So instead of:

60 90
100 0
210 90

Use:

60 90
61 0
209 0
210 90

That will make the jump from an altitude of 0 to 90 much more "straight."

The second thing is a trick, and it won't be perfect, but it should help. What type of mount are you using? Is it an alt/az mount, like a Dob? Or is it an EQ mount? If its an Alt/Az mount, you can set the Dobson's hole at the zenith. I'm not exactly sure where your maximum altitude is from your chart, but lets assume its 70 degrees.  The radius of a Dobson's hole that extends from the zenith to 70 degrees would be 20 degrees. So you would enter twice that (40 degrees) in the telescope setup for the Dobson's hole.

By putting these two things together you should be able to eliminate most of the sky you can't see. You won't get a straight line across just like your roof, but it will be fairly close.
Thank you
Is an sct c11
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#6
If you are using your scope mounted equatorially, then the Dobson's hole option doesn't apply. In that case you will just have to keep in mind that things that are overhead aren't accessible. You can pick targets from a chart, for example, or see how long it takes after the SkyTools "start" time for objects overhead to typically appear below your roof, and add that amount of time for objects near the zenith.
Clear skies,
Greg
Head Dude at Skyhound
Reply
#7
(2021-11-11, 07:10 PM)theskyhound Wrote: If you are using your scope mounted equatorially, then the Dobson's hole option doesn't apply. In that case you will just have to keep in mind that things that are overhead aren't accessible. You can pick targets from a chart, for example, or see how long it takes after the SkyTools "start" time for objects overhead to typically appear below your roof, and add that amount of time for objects near the zenith.

Thanks. Forgot to say is CPC (no equatorial)

I will try that.
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