Establishing VPs and horizons in Landscape photos?


#18

I see a problem with the last diagram that I drew. It shows a distance between the eye and the picture plane as it was based on drawing sketches to scale. I’m guessing the setup will be different with a camera as I’d image this length would be the lens focal length.

Nick if you had time to draw a sketch that would be sound.

Shawn, I’ve got no woes with buying a book on this - would you mind explaining a little about what the book describes for this process? And is it without the use of software? I thought matchmoving was purely for video. I won’t necessarily have stereo images otherwise I just use imagemodeler or matchmover.

Working in engineering, it would be quite reasonable to have these factors to work with:

  1. image with metadata alone or

  2. image and gps data for image

  3. image, gps and site survey

  4. stereo images and any of the above

But I want to be able to deal with the worse option which will often be the case.


#19

The book covers too much to enter here. But it shows the old way of how to use any CG rendering software that has camera lens settings to solve how a photo was taken and be able to add assets into the image so that everything is in scale and lines up correctly. That’s how I used to do things in the '90s before matchmoving software arrived.

Maybe someone has written an online PDF that shows the same thing? But it would have been written a long time ago though, and not be hosted anymore.


#20

Yeah I know the technique you are describing then, it is a common one in vfx and matchmoving. What we are talking about is very different, did you see the diagrams MisterS posted up? What he would like to do is be able to draw by hand (on paper, without any 3d software) an image that is in perfect perspective and is drawn as if from a specific camera position, with a specific camera focal length. It should be entirely possible to do this without touching a computer, and if you are good at it then you can design objects on paper, give them to a modeller, and there should be absolutely no need for the modeller to have to eyeball the camera to match your design on paper as you described. You can give him a camera position and focal length and it will match without any problems.

I should be able to have a look at your diagram today, ill see if i can dig out some of my old perspective exercises and post them up too, they may actually be at work though, ill have a look on Monday…


#21

Oh. If you’re drawing a scene from scratch on paper that needs perspective and vanishing points and curvachure on the horizon and on edges of buildings, there are tips everywhere for that. Marvel may have something online from the '70s still. Any drafting for illustration books will explain it, also.


#22

I’m after a specific setup, ignoring the earths curavature at this stage, on how to produce a perspective drawing with a specific field of view, I can then reverse engineer that I guess to overlay onto a photograph.

Dude, you kind of come across like you know it all but there’s no substance to your replies - they’re just becoming irritating. If there are tips litterally everywhere on that, why don’t you just share! or move on!

Nick - cheers for helping out, if you find those sketches then that will be sweet.


#23

All those things are what MisterS is already doing. Did you look at the diagrams?
It’s actually a lot harder than I expected to find good material on this subject. I have a number of books on perspective but they all either get to a certain level of complexity and then assume that’s good enough, or they get very in depth but dont really relate is back to real world cameras. Books on perspective can be phenomenally hard work to read through as the ideas are quite conceptual and take considerable explaining… On that note, Gnomon just released 3 training dvds on perspective construction. I haven’t had a chance to have a look at them yet, but gnomon generally have a high standard so check those out if you get a chance!


#24

I saw those - and yes Gnomon DVDs are usually pretty good. This is the second perspective book that I’ve bought and am reading - not sure I want to commit to 3 DVDs though on the subject. I’m already mid way through a matte painting course, so the dollars add up.


#25

Yeah they arent’ super cheap, I can understand that.
Anyway, I had a perspective grid that I had drawn out for practice here at work, and it illustrates how to position a specific field of view. Notice that your vanishing points (VP’s) can move around freely as long as they remain a 90 degree angle from the station point (SP). That is how you can rotate an object but still make sure that the perspective is in the same world. Your field of view is created in the same way as the vanishing points, but can be any angle you wish. In this case I chose 60 degrees which is about the same as the human eye can see. Where this intersects the horizon, I made a large circle that touches both points. I then created a 1.778 framing within this 60 field of view, which is HD resolutions normal aspect ratio. The only thing I’m not 100% sure of is this: The field of view is actually a cone of vision, hence it is round, but to get a framing that is the same field of view, I’m not sure whether the framing should meet the edges of the cone of vision on its sides and extend outside this on its corners, or whether it should remain fully inside. Only real way to test is to reverse engineer a 3D scene and see how it works. But depending on the camera that you are theorising to have shot this image that you are drawing, you can get the rest of the info on the cam and use that to figure out exactly what lens this would be.

Let me know if anything doesn’t make sense. I’ll try and put up an actual drawing soon that uses this stuff to create a final image…

N

EDIT: The uploader seems a bit screwed at the moment, I can’t upload the image, will try again later, what this space…


#26

Any joys on that diagram?

You could always email it to me if you’re having woes trying to upload. I get that sometimes though thought that was due to dodgy aussie internet connections. UK is pretty swift though. :slight_smile:

david_spittle at hotmail dot com


#27

Sorry to leave you hanging, I never got around to trying the upload from home, I’ve been working pretty long hours trying to get a shot done so haven’t had time to do it (i know, a three minute job, just got pushed down my list of priorities :banghead: )
Unfortunately the time i tend to check this forum is when i am at home, whilst the diagram is still at work… I’ll either get a working upload or send it through to your email tomorrow over lunch.


#28

Hey, no worries, there’s no hurry. :slight_smile:


#29

Here we go:


#30

Slightly sharper?

For larger, go to this link:

http://imageshack.us/a/img203/9403/perspectivegridcgsociet.jpg


#31

A couple of things I didnt mention before. The grid that I drew out for the ground plane consists of perfect 1m X 1m squares. Its also easy to measure exactly what distance any point in the scene is from the camera.
One other thing I need to find out about regarding field of view is that i know in this image I have plotted a 60 degree cone of vision and translated that into a HD aspect ratio framing of the same field of view, but I have only seen the field of view constructed from where the 60 degree field of view lines intersect the horizon. This makes for pretty uninteresting framing, I need to do some research into how the FOV changes when the camera is pointing up or down. I would imagine it should stick to the lines and then at the horizon the lines should converge again at the same angle above ghe horizon? I’m not entirely sure, perhaps someone else here has the answer?
If the perspective setup here isn’t clear, tell me and i’ll try and explain more clearly :slight_smile:

N


#32

Sorry for the delayed response - I’ve been away for a few days. I’m off on holiday again on Wednesday - not sure if I’ll have time to experiement with this before I go but I’ll be in touch shortly after I get back. I’ll see if I can work out how to adjust the horizon line or see if I know anyone that can help.

Much appreciated for the info, thanks a lot.


#33

Hey

I just looked in my book and this is actually covered very briefly, I didn’t know what I was looking for before but ‘perspective Cone of vision’ has thrown up a few diagrams on google too.

I’ve not got time before my holiday to get my head around it properly, but I think this is what we’re looking for.

I’ll CAD up some diagrams soon and post here, sorry the res is pretty low.


#34

I’m not sure if this is correct. The bright yellow lines indicate the tilt of the camera, in this case 8 degrees measured against the horizon line.

One yellow line is measured 90 degrees to the other at E2 on the RHS and should give another vanishing point - (but does it really>?!) what that does, I don’t know! It can’t be verticals as they’d be going the wrong way which makes me wonder whether this is completely wrong.

So this may (or may not) demonstrate how to draw a white square in the correct perspective using 45 degree VPs and ignoring the converging lines that exist in the photo (as that would defeat the purpose of the excersise)

So I’ve tilted the ground rather than move the camera… I think…

I guess next is - how to get your vertical VPs.

Blue = FOV 58degrees
REDs = 45VP, the faded one level with the COV measured 45degrees, and the darker one at the horizon, squished a bit.

The other lines are to measure along the arbitary ruler at the bottom, so the closest corner of the square begins 2 units right and 1 back. helped by the 45measuring points.

Is it correct…?


#35

So the above diagram is correct apart from the yellow lines. Can’t find the orig PSD to edit.

Anyway, move the yellow lines up to the next horizontal (faded) green line, and flip vertically, this will give you your vertical vanishing point. I tried it on a new sketch and it worked - well at least it looks right!

And this helps too:

http://epicgames.com/community/2012/11/free-art-tool-released-thanks-to-epic-friday/


#36

Hey, sorry it’s been a while! The diagram looks good, interesting method there to get the vertical vanishing point. I’ll have to deconstruct a 3D scene at some point so I can do some exhaustive testing to see exactly how to get a specific camera FOV, but the diagram you found offers some good insight, thanks for that. Look forward to testing all this stuff out when I get a chance.

N


#37

Your diagram was correct to use the camera’s FOV to establish the CP, and from there the rest of the diagram can be drawn.

And to get the FOV, you’d need some converging lines and then construct the diagram in a different order from that.