Planet roundness issue when planet is not in the center

[nethskie]

Hi guys can you help me figure out how to resolve this? when i'm rendering a planet when i put it on the left or right side (not centered) the shape of the planet is becoming distorted (stretched) or not that round i already tried playing with the camera settings but no effect. Is there a work around for this? i checked some renders here and on deviantart and it seems i'm not the only one having this issue. I'm using TG2 2.4 free version by the way... thanks

[Kadri]

Did you looked here , Nethskie ?

http://www.planetside.co.uk/forums/index.php?topic=14364.msg140694#msg140694

[Dune]

I'll say a word about this. The problem is that the eye has a certain angle of viewing, and for a natural looking landscape you'd have to use that angle. As soon as you reduce that, you get a telephoto lens idea and the distance is reduced, the image gets 'flatter'. But that angle also gives distortion. I noticed that very much in my medieval city, and I would love a TG 'lens' that could annihilate/reduce the lines towards the vanishing point in the center of the planet. But I'm quite sure that's hardly possible.

[bigben]

You can use panoramic stitching software to remap your image to a cylindrical projection which should make your planets round.  http://archive.bigben.id.au/tutorials/360/background/images/cylindrical.jpg  If you do, you may want to increase the height of your render to allow for cropping later on.

[nethskie]

@Kadri

I'm using the default FOV i tried to lower it but it is changing the planet position i'm aiming for. For me this problem is worse because even my eclipse raw renders when placed not in the center the planet02/moon looks warped and would make the post work harder than it should be. This issue is also limiting me in creating a scene with multiple planets because planets in the sides looked oblong or elongated.

[bigben]

Get a round ball, take a photo of it with a camera using a standard or wide angle lens, with the ball near the corner of the image.
Look at the shape of the ball....  same thing.  1. It's normal, not a fault with TG or any other renderer 2. It gets worse the further away from the centre of the image you place the sphere.

[Kadri]

You could plan your image before and put the important part more in the center and make a crop render.
Maybe not usable all the time and i didn't tried this so a am not sure if this will work but in theory you should get less distortion in this way.

This isn't a problem for me so i didn't much bother about this but you could find a workflow with post lens correction or as Ben said with stitching software etc.

http://forums.cgsociety.org/showthread.php?t=872687 
http://www.dxo.com/en/photo/dxo_optics_pro/features/optics_geometry_corrections/distortion
https://www.seas.harvard.edu/news-events/press-releases/flat-lens-offers-perfect-image

Maybe others who are more onto photography or Matt could make better suggestions about this.
He works on movies too so he probably had first hand experience with this kind of problems.
I am curious what he thinks about making TG2 images distortion free with a new lens option etc.

[bigben]

Not quite... It's not really a case of lens correction. The distortion referred to on most of those pages refers to deviations from the ideal rectilinear projection.  CG render engines use the math required to create the exact projection so they don't suffer from pincushion/barrel distortion.

Here are some screengrabs from PTGui showing remapping of a 120° render from TG
1. Rectilinear (ie, what TG creates
2. Cylindrical
3. Equirectangular

There are many other projection types but these last 2 will keep planets round. It's obvious that if you use this method, you will probably want to render some extra space around your scene to allow for the change in shape of the image.

[Kadri]

Thanks Ben good to know 

[nethskie]

Thanks guys i finally understood that the final work around would be really post edits. I have successfully made the image I wanted.



http://www.planetside.co.uk/forums/index.php?topic=15053.0

[Oshyan]

And a gorgeous image it is!

- Oshyan

[Dune]

Thanks Ben! But what would happen to a straight horizon in cylindrical or Equirectangular remapping? It would probably bulge down. So if I want to make a city with all vertical lines, all the way from left to right and a straight horizon, I'd best make three or more (larger than necessary) renders with different camera angles and stitch those together, like you would in photography.

[bigben]

A new (old) projection was added to some panoramic software a few years ago... vedutismo (aka pannini). This provides a great compromise for ultrawide angle images >120° (and even >180°).
http://vedutismo.net/
Projection comparison
http://www.flickr.com/photos/ben-kreunen/3425343943/in/set-72157616445270083
My Original projection comparison with notes
http://archive.bigben.id.au/tutorials/360/background/projections.html
Remapped images taken with full-frame fisheye
http://www.flickr.com/photos/ben-kreunen/sets/72157627460745756/

When creating ultrawide angle renders I'd probably use a maximum of 90-100° and tile renders to get the rest of the width
For correcting verticals you also have to specify the pitch for each tile when stitching.
.. and yes, it pays to render a greater fov than your final image to allow for the fact that the remapped image usually won't be rectangular and will require cropping.

[bigben]

Thanks guys i finally understood that the final work around would be really post edits. I have successfully made the image I wanted.

Nice and clean for a desktop image.