[Tom Bishop]

Are you standing by your point that Stellarium shows that the stars don't maintain their angular separation as they rotate? It's a really simple question.

I haven't seen any evidence that they do. If you think so, I look forward to you providing the compelling evidence for your topic of interest.

That’s not what you said though, is it?

You said they didn’t, and you offered a laughably pathetic attempt at science to justify your statement.

That’s not the same thing as saying you haven’t seen evidence that they do, is it?

So, again, are you standing by your statement, or are you admitting you were wrong?

Nope, I wasn't wrong at all. I looked at Stellarium and couldn't find circular star trails.

I do see that you have neglected to prove that the polar layout would produce distortion, that every layout produces distortion, or find the one which does not prove distortion. So far the evidence you have produced for your circular star trails remains at zero.

[SteelyBob]

Nope, I wasn't wrong at all. I looked as Stellarium and couldn't find circular star trails.

So you’re standing by taking linear measurements on a picture which has the normally flat line of the horizon wrapped around in a circle? You don’t see a problem with that exercise?

[Tom Bishop]

Nope, I wasn't wrong at all. I looked as Stellarium and couldn't find circular star trails.

So you’re standing by taking linear measurements on a picture which has the normally flat line of the horizon wrapped around in a circle? You don’t see a problem with that exercise?

No. I just see a misunderstanding of the polar projection, and planispheres. If you were representing the sky on a piece of paper you would do so on a circle.

[SteelyBob]

Nope, I wasn't wrong at all. I looked as Stellarium and couldn't find circular star trails.

So you’re standing by taking linear measurements on a picture which has the normally flat line of the horizon wrapped around in a circle? You don’t see a problem with that exercise?

No. I just see a misunderstanding of the polar projection, and planispheres. If you were representing the 180 degree view of the sky on a piece of paper you would do so on a circle.

Indeed you might choose to do that. But if you were to attempt to use a ruler to try to infer the angle subtended at the eyes of an observer between any two points, then other than cases involving measurement from the centre of the azimuthal projection, you will get a wrong answer. As you have done in your example.

You don’t need to even understand azimuthal projections to grasp this - it’s pretty obvious if you think about it.

[JSS]

Yes, that's what an extreme fisheye does. But many lenses, in fact most have only minor distortion in the center, and get worse at the edges and especially the corners.

There were straight lines all across the entire image at various angles. You keep repeating your weak argument.

The only reason I'm repeating myself is you are not listening.  Drawing a handful of short lines on a cropped image doesn't prove anything.

Worse, there is a bigger problem here than your lines. How do you know the photographer didn't adjust the picture after taking it to make the curved lines of the bridge straight?

I know if I was going to make a picture to sell or display, I'd straighten out the bridge as it would look better.  Can you prove the artist didn't do this?  How?

I haven't seen circular star trails in Stellarium, and nor would Stellarium be a real world observation enough to count as compelling evidence for perfectly circular star trails.

You should learn to correctly operate the software you use to try and prove your points.

As has been stated many times, the circular star trails produced by Stellarium are indeed compelling evidence since you can use that software to predict the position of the stars anywhere in the world, take pictures and compare them with yours. They will match. That's pretty compelling.

I just see multiple claims here. I haven't seen demonstration of these claims. I look forward to you demonstrating each and every one of your claims beyond dispute.

Claims that anyone with a camera and free software could easily prove for themselves. Have you tried it?  What were your results?

If I showed you a photograph that I took, and a matching screenshot of Stellarium that matched the stars displayed, would that suffice for a demonstration beyond dispute?

[Tom Bishop]

Nope, I wasn't wrong at all. I looked as Stellarium and couldn't find circular star trails.

So you’re standing by taking linear measurements on a picture which has the normally flat line of the horizon wrapped around in a circle? You don’t see a problem with that exercise?

No. I just see a misunderstanding of the polar projection, and planispheres. If you were representing the 180 degree view of the sky on a piece of paper you would do so on a circle.

Indeed you might choose to do that. But if you were to attempt to use a ruler to try to infer the angle subtended at the eyes of an observer between any two points, then other than cases involving measurement from the centre of the azimuthal projection, you will get a wrong answer. As you have done in your example.

You don’t need to even understand azimuthal projections to grasp this - it’s pretty obvious if you think about it.

I would need to see more evidence that it is impossible to portray the shapes an observer sees when looking up at the domed concave celestial sky onto a flat circular plane.

Here is an inverse example with a RE globe. If you are looking down at a globe and saw the great lakes in the shape of a circle for argument's sake (drawn orange circle), why don't you think that this circular shape can be maintained in a projection?

https://gisgeography.com/azimuthal-projection-orthographic-stereographic-gnomonic/



It literally says that this projection simulates what the observer would see from that position over the globe.

If the observer is hovering over the globe (if it was a globe) and sees the shape of a circle in the United States (orange circle) from that position, why shouldn't it also be a circle in the associated flat projection described?

[Tom Bishop]

The only reason I'm repeating myself is you are not listening.  Drawing a handful of short lines on a cropped image doesn't prove anything.

Worse, there is a bigger problem here than your lines. How do you know the photographer didn't adjust the picture after taking it to make the curved lines of the bridge straight?

You know that there are lines all throughout this image:



Oh, but now it's "cropped" and was adjusted in post-processing. What happened to your argument about distorted lenses? You were arguing:

I am saying that you can not use random images off the internet to prove or disprove stars move in circles or ellipses. You don't know how the picture was taken or how it may have been processed.  Your random internet images of elliptical stars are not reliable, and other random images of circular images are not reliable. Because you don't know enough about either.

Incorrect. If there are references in the image, you can see if the lens is warped or not.

No, you can not.  Did you forget the picture I posted showing the blinds?  There were straight lines there, and very obviously warped ones.  Unless you think my blinds actually look like that.

It appears that you have conceded this argument. I said that if there are references in the image you can see if the lens is warped or not. You couldn't counter this argument.

You could not maintain that argument about distorted lenses so therefore you have to argue something different and imagine other processing effects. Therefore I was correct. You can indeed tell if it's a distorted lens by looking at the lines throughout the image.

[JSS]

The only reason I'm repeating myself is you are not listening.  Drawing a handful of short lines on a cropped image doesn't prove anything.

Worse, there is a bigger problem here than your lines. How do you know the photographer didn't adjust the picture after taking it to make the curved lines of the bridge straight?

You know that there are lines all throughout this image:



Oh, but now it's "cropped" and was adjusted in post-processing. What happened to your argument about distorted lenses?

Yes Tom, you cropped it. Are you denying you cropped the image you posted below? Cropping means selecting a smaller section of a large image. Pay attention.

The argument is we do not know what kind of distortions the lens has and if it was adjusted in post processing.  Unless one of us contacts the photographer, there is no way to know.  That's my point.

You can't maintain that argument about distorted lenses so therefore you have to argue something different. Therefore I was correct, and you can indeed tell if it's a distorted lens by looking at the lines throughout the image.

No, you were not correct. You can not determine the amount of distortion in one part of an image by measuring some lines elsewhere like you did.

I see you ignored my offer to demonstrate my claims, again. If you are going to demand people demonstrate their claims, it's rather rude to constantly ignore them when they offer to do so.

[Tom Bishop]

Nope. Do the lines over any of the image. They're straight. They're straight because it is a rectilinear lens.

You are shifting from arguing about the distortion caused by lenses and are arguing about post-processing. This is a different argument than the "lenses can cause distortion" argument you have been peddling. I said "If there are references in the image, you can see if the lens is warped or not." You replied with "No, you can not." If you can't maintain your argument you lose.

[JSS]

Nope. Do the lines over any of the image. They're straight. They're straight because it is a rectilinear lens.

You are shifting from arguing about the distortion caused by lenses and are arguing about post-processing. This is a different argument than the "lenses can cause distortion" argument you have been peddling. I said "If there are references in the image, you can see if the lens is warped or not." You replied with "No, you can not." If you can't maintain your argument you lose.

It's the same argument: Measuring lines tells you nothing about the scene as you lack the information to determine that.

It doesn't matter if it's because the lens is curved, or post processing, optical illusions or any other reason. You have no way to know, therefore it's not proof.

Again I challenge you, how can you prove the lines are straight because that's how the picture was taken, or because it was post processed to straighten them out?

No you can't.  Drawing a few lines in the center of the image doesn't help determine the curve at the edge.  It doesn't tell you what part of the image was straight and now bent, and what was bent and now straight.

You keep claiming it was taken with a rectilinear lens.  Source?  Not that it matters in the least as was proved to you earlier, they also have distortion, which you also seem to have forgotten.

Also, are you ever going to respond to the following?  You made a demand, I responded, and you have ignored it multiple times now.

I just see multiple claims here. I haven't seen demonstration of these claims. I look forward to you demonstrating each and every one of your claims beyond dispute.

Claims that anyone with a camera and free software could easily prove for themselves. Have you tried it?  What were your results?

If I showed you a photograph that I took, and a matching screenshot of Stellarium that matched the stars displayed, would that suffice for a demonstration beyond dispute?

So, would you?  If I provide you with a screenshot and a photo I took that line up, will you accept that Stellarium produces accurate output?

You could also do this yourself, as I said. The only reason you haven't seen any demonstrations is because you don't want to look.  I'm not proposing anything extreme here, just that software widely used to predict the positions of stars does what it says.

[Tom Bishop]

Nope. Do the lines over any of the image. They're straight. They're straight because it is a rectilinear lens.

You are shifting from arguing about the distortion caused by lenses and are arguing about post-processing. This is a different argument than the "lenses can cause distortion" argument you have been peddling. I said "If there are references in the image, you can see if the lens is warped or not." You replied with "No, you can not." If you can't maintain your argument you lose.

It's the same argument: Measuring lines tells you nothing about the scene as you lack the information to determine that.

It doesn't matter if it's because the lens is curved

Wrong again. Measuring these lines tells you that there is lens distortion in the image.

The rest of your post speculating about possible post-processing is irrelevant to this point you keep insisting on, and which you continue to be wrong about. It is possible to tell if there is lens distortion with straight lines in the image.

[JamesonM]

I read this thread with interest. I’m an amateur astronomer and do some astrophotography. I use stellarium (I saw some other threads wondering about it’s validity). Star trails are a problem we fight in astrophotography regularly because they ruin long exposure images. Anyway, I can take a video of myself setting up and capturing a celestial object if that helps. I’d do it live - so no modification involved. It’s just a refractor and cmos camera, so nothing tricky.

[JSS]

Nope. Do the lines over any of the image. They're straight. They're straight because it is a rectilinear lens.

You are shifting from arguing about the distortion caused by lenses and are arguing about post-processing. This is a different argument than the "lenses can cause distortion" argument you have been peddling. I said "If there are references in the image, you can see if the lens is warped or not." You replied with "No, you can not." If you can't maintain your argument you lose.

It's the same argument: Measuring lines tells you nothing about the scene as you lack the information to determine that.

It doesn't matter if it's because the lens is curved

Wrong again. Measuring these lines tells you that there is lens distortion in the image.

You took one image, measured straight lines in part of it and claimed the rest of the image is not distorted.

Well, look at the blinds. I can measure several straight lines, can I claim the rest of the image is not distorted?

Prove I don't have curved blinds.

Prove the middle blind isn't actually curbed and I post-processed it to make it straight?

You can't do any of these, just as you can't tell in your star trails picture what the original geometry of the scene was after lens distortion and unknown 'curve corrections' which as you stated earlier, must mean a picture is not showing reality.

The rest of your post speculating about possible post-processing is irrelevant to this point you keep insisting on, and which you continue to be wrong about. It is possible to tell if there is lens distortion with straight lines in the image.
[/quote]

It's entirely relevant, as it's my main point.  You can't know what the original scene looked like from a picture with unknown properties and unknown transformations.

I'm speculating there likely have been corrections made. You are speculating that there have not. The POINT is that neither of us can prove it, therefore the photo is useless as proof of what you claim.

[Tom Bishop]

Prove I don't have curved blinds.

Your arguments just get worse and worse.

Lets just end it here and let anyone reading decide whether it is reasonable that you have curved blinds and that the lines on the structures of a metal bridge are curved in just the right way to look straight to a distorted camera lens. 

[JSS]

Prove I don't have curved blinds.

Your arguments keep getting worse and worse.

Lets just end it here and let anyone reading decide whether it is more reasonable that you have curved blinds and that the lines on the structures of a bridge are curved in just the right way to look straight to a distorted camera lens. 

You are misrepresenting my point, again.

Everyone knows it's reasonable to assume I don't have curved blinds.

But from that picture, they can't PROVE it.  Something being reasonable isn't proof.  I could have hand-made some curved blinds which is an unreasonable thing to do, but possible. But from that photo nobody can prove it.  Just as you can't prove stars go in ovals just because you found a distorted picture. It doesn't matter if you think it's a reasonable assumption or not, it's not proof.

My arguments are fine, your interpretation and misunderstanding of them is the problem.

[Tom Bishop]

Prove I don't have curved blinds.

Your arguments keep getting worse and worse.

Lets just end it here and let anyone reading decide whether it is more reasonable that you have curved blinds and that the lines on the structures of a bridge are curved in just the right way to look straight to a distorted camera lens. 

You are misrepresenting my point, again.

Everyone knows it's reasonable to assume I don't have curved blinds.

But from that picture, they can't PROVE it.  Something being reasonable isn't proof.  I could have hand-made some curved blinds which is an unreasonable thing to do, but possible. But from that photo nobody can prove it.  Just as you can't prove stars go in ovals just because you found a distorted picture. It doesn't matter if you think it's a reasonable assumption or not, it's not proof.

My arguments are fine, your interpretation and misunderstanding of them is the problem.

Everyone also knows that it's reasonable that the lines on a metal bridge or similar structure are straight, and not curved in the right amount to look straight to a distorted camera lens.

Your arguments are poor.

[JSS]

Prove I don't have curved blinds.

Your arguments keep getting worse and worse.

Lets just end it here and let anyone reading decide whether it is more reasonable that you have curved blinds and that the lines on the structures of a bridge are curved in just the right way to look straight to a distorted camera lens. 

You are misrepresenting my point, again.

Everyone knows it's reasonable to assume I don't have curved blinds.

But from that picture, they can't PROVE it.  Something being reasonable isn't proof.  I could have hand-made some curved blinds which is an unreasonable thing to do, but possible. But from that photo nobody can prove it.  Just as you can't prove stars go in ovals just because you found a distorted picture. It doesn't matter if you think it's a reasonable assumption or not, it's not proof.

My arguments are fine, your interpretation and misunderstanding of them is the problem.

Everyone also knows that it's reasonable that the lines on a bridge or similar structure are straight, and not curved in the right amount to look straight to a distorted camera lens.

Your arguments are poor.

Again, it doesn't matter what is reasonable or not.  Everyone knows it's reasonable to think the Earth is round, will you accept that line of reasoningtoo?

To me, it's reasonable that the lines on a bridge using a wide angle lens will look curved, and if they are straight it means some post-processing correction was applied.

Reasonable doesn't matter.  Can I prove it?  No.  Can you prove it?  No.

[Tom Bishop]

Again, it doesn't matter what is reasonable or not.

Actually, it does. It's an increasingly desperate argument to resort to that. Your desperate arguments now have you calling for the possibility of curved blinds and metal bridges curved in just the right way so that it seems straight in the right places to a distorted camera lens. You are arguing this so you can justify your argument.

This 'possibility' is just garbage. You are spamming our forum. Kindly stop.

[JSS]

Ok, here is another picture to illustrate my point that if you don't know the details, you can't prove what the shape of an object in a picture is.

In it is a ruler and a cable. That cable may be straight, it may be curved up, it may be curved down. Maybe both.

A challenge to you, Tom. Based on the ruler which I assure you is straight in reality, tell me which way that cable is curved and by how much and how you have determined this.

If you can't determine if or how the cable curves, how can you determine it the oval curves of those star trails is real?

[JSS]

Again, it doesn't matter what is reasonable or not.

Actually, it does. It's an increasingly desperate argument to resort to that. Your desperate arguments now have you calling for the possibility of curved blinds and metal bridges curved in just the right way so that it seems straight in the right places to a distorted camera lens. You are arguing this so you can justify your argument.

This 'possibility' is just garbage. You are spamming our forum. Kindly stop.

Please see my post above.

Also, pay very close attention to what the words 'reasonable' and 'possible' and 'proof' mean.  Saying something is reasonable is not proof.

I am not calling for the possibility of bridges curving, I have stated clearly that the image produced will be curved, and is often corrected.  Distortion correction is almost required with wide angle lenses if you want straight lines.  Find me a 180 degree wide angle that produces completely straight lines with no distortion. It does not exist.