Horizons

XenBear

Hey there,

I've got a quick question about horizons, how do you work out where they are in an image? I really need to know this as it makes creating environments a whole lot easier and from the looks of things realistic.

It is easy to figure out where the horizon is on some images as they are visible but what about enclosed environments? For example how do you work out where the horizon is on this image?


Thanks a lot.

divi

it's harder on pictures like that since you can't really say which horizontal parts of the building are built exactly a) parallel to each other and b) parallel to the horizon in reality which means that you can only really make an approximation. so you kind of decide which parts you want to use that feel as parallel to the ground as possible. example would be the building furthest to the left. draw a line that spans all across the image and that's parallel to the top of the window. another line at the bottom of the same window and another line where the brick wall meets the ground. if everything is actually build parallel in reality they will meet in one point and thats where you draw a straight horizontal line that represents your horizon.

hope it makes sense somehow .
cheers

edit: another somewhat quicker but less exact way would be to juse make a guide in photoshop and check what feature in the image aligns with it. the crack between rows of bricks work quite nicely for that in the picture you have there. it has to be done on something that sits in an angle to the camera like the house on the left though

renderhjs

one way would be to follow all perspective vectors of 1 axis and use their average screen crossing point as y- screen coordinate of the horizont somewhat like this:

Zwebbie

The horizon is always at the height of your eyes; or in this case, the lens of the camera.

Here are my 2 cents. A straight line should indicate the horizon, if the object is placed correctly anyway.

Vailias

Zwebbie: height yes, but if the camera or your head is tilted at all, the horizon changes its level in the scene.

I think renderhjs has got it right, as if you look at the lines in the grass, where the grass is level they point to about the same area.

XenBear

I'm kinda getting it but bear with me (it is a stupid question). How do you know where to draw the perspective lines in the image?

jocose

Perspective lines can be drawn along any shape that share the same plane of perspective. It's usually easiest to look for lines that are normally straight (like the bottoms of the roof, bottoms of buildings, the top of the roof). If you draw lines along the angle of these far out enough you will notice that they all terminate at a single vanishing point.

You know your drawing the lines right if they all intersect at the exact same point.

This is probably my favorite tutorial on perspective. Read it carefully if you are still confused:

http://www.khulsey.com/perspective_basics.html

XenBear

Oh, right thanks. That article cleared a lot of stuff up for me, I think I get it now. Thanks again everyone.

Ben Apuna

That link jocose posted is pretty good place to start. XenBear if you want to pursue perspective in more detail you should check out this book. [ame]http://www.amazon.com/Perspective-Made-Easy-Ernest-Norling/dp/0486404730/ref=sr_1_1?ie=UTF8&s=books&qid=1240379176&sr=8-1[/ame]

XenBear

Ok I'll read it if I can get my hands on it, thanks.