Hi all,

I need to work out a method for matching perspective in 3d scenes (Poser) to the perspective in 2d images.  Didn't find any easy buttons for this, so I'm making up my own.

Seems like what I need to do is establish vanishing lines, trace them back to the horizon line, and then try my best to eyeball my 3d perspective into place with the perspective guides in Poser.

So, right now I'm working on how to get those vanishing lines extended all the way to the horizon.  Obviously I increase the canvas size.

Then, the best I can come up with is using the line tool to follow whatever straight architectural-type lines I have.  Trouble is, to be accurate I have to zoom in as far as possible, which means I can't make the line very long.  When I zoom out, I can barely see the line, so I can't accurately use the line tool again using the original as a guide.  Is there a way I can automatically turn a line segment into a ray, for lack of a better term?  That is, take the line segment I've made and extend it out to infinity?  If I need to use a different tool, maybe a vector tool, that's fine too, the task remains the same.

Hmmmm, this should work.
Use a paint brush, zoom in tight and just left click on the spot you want...then zoom out and hold down the ctrl button and left click again. You should have your long line at that point.

Hope this helps.

Sorry, I don't follow.  How would a paint brush create a line?  And how would that line be parallel to the original line?

If you're on CS2, there is the Vanishing Point tool in Filters that will do what you want without having to draw the extra lines. The Help section has a detailed explanation of how to use it.

If you wanted to make it parallel you could just copy it and move it up or down, right?

Grab the paintbrush and make a left click somewhere on the page. Now before you click again hold down the ctrl key, move your mouse cursor to another location and then left click once. You should see a line appear between your first left click and you last one.

Bushi is correct too. 
A lot easier than what I'm suggesting, but it really depends on what the circumstances are.

Hope this helps.

I'm on CS2, and I read the help section on VP, but It doesn't seem to do what I need.  All it seems to be able to define is planes, not lines, and it doesn't seem to offer any help with my problem, which basically is how do I place vanishing lines accurately when I need to zoom way out to see both ends of the line I'm drawing, yet zoom way in to see that I'm placing the line accurately?

Illustrator also doesn't seem to have jack shit for this simple artist's task which on a drawing board would take all of two seconds, given a ruler and a pencil.

Sorry bushi, I'm not cursing at you - I'm just really getting tired of simple crap that takes teeth-pulling to get done.  I'm open to suggestions, obviously.

Quote - If you wanted to make it parallel you could just copy it and move it up or down, right?

Yes, I thought about that, but this is a task I want to be able to repeat quickly, as I'll be doing it a lot.  With perspectives that have VPs way off (most of the time), this makes the process unworkable.  (also, not to nitpick, but to ensure clarity, I'm not so much interested in parallel lines as I am in simply extending an existing line - I know, that's still parallel, but you know what I mean I think).

I tried to transform a shape I'd made with the line tool in Illustrator (transform>scale), but for some reason illustrator destroys the angle of the line in the process.

I tried making a line segment covering just the line as it appears in the photoref (here, a window sill), then turning it into a guide, turning on snap, and making a new, longer line but that doesn't seem to do jack either.

Quote - Grab the paintbrush and make a left click somewhere on the page. Now before you click again hold down the ctrl key, move your mouse cursor to another location and then left click once. You should see a line appear between your first left click and you last one.

No, when I hold down CTRL the cursor transforms into the move layer tool, and when I left click again elsewhere nothing happens.

My mistake.
Do everything I said except hold down the shift key not the ctrl key.
My bad.
Then everything should work as I said.

That's a neat trick, but it still doesn't help.

I want to make a line, then elongate it (without thickening it or changing its angle) to arbitrary lengths (to infinity, or rather the limits of the canvas).

(doesn't this seem waaaaaay too simple a topic for a forum thread?  :P :( )

Using guides would be the obvious solution except they are only horizontal or vertical in photoshop. (unless I'm missing something) Can you take the image to Illustrator or Coreldraw where the guides can be any angle and this would be waaaaay too simple. :biggrin:

I'd try the pen tool. (open paths palette) select the pen tool click once for start point. click a second time for end point. it's one dimensional, feel fee to scale it.  click the (path selection) tool. click on your image. click the pen tool, click once for start point. click a second time for end point again on a different angle. (path selection tool) can move the two lines to line up with 2 edges. edit transform- scale... the intersection should give you a vanishing point.

i can't edit that post now...

find an edge,
craft a line with the path tool along that edge
scale and/or transform that line.
deselect all paths
repeat.