[Sumaleth]

Row.

[morphgfx]

i've just spend a few hours on one question:
when using the method Ben Barker explained above, how do i find a second non-parallel cube, that is viewed from the same position as the first one? just choosing 2 different vanishing points obviously don't work. Once again: i don't want to do any projection stuff to find my vanishing points and cubes. just one cube and then finding another NON-PARALLEL one that fits to the first in perspective. is there any other way to do this than just drawing a cube that "feels" right?

@spooge: i was under the first 15 i think, but since i had a lot work to do the last 2 days and then spent way to much time on trying to figure out a solution for my problem described above instead of just doing the projection thing, feel free to crit someone who already finished his cubes .

[Sumaleth]

Morph:

Check out the third tute on Francis's site (Spooge links it in the first post of this thread). It shows how to project down two cubes so that they have the same field-of-view relative to the viewer.

If your "view plane" line (on Francis's diagram thats the horizontal one just touching the point of the cube seen from above) is -touching- an edge of the cube (as in Francis's image, then that vertical edge in the 3D view will be 1:1. This is how you get the height of the first cube.

Getting the height of the second cube can probably be done a lot of ways, but I extended one of the edges of my "known" cube across to the second one and that gave me enough measuring points to work out the height of the back cube.

Row.

[morphgfx]

many thanks Sumaleth
but is there any way to find a cube that have the same field of view relative to the viewer, like you said, without using the projection method described in Francis' tutorial? for example if you want to find a cube thats "fits" to another and you want to work in "3d-view" only? its kinda hard for me to describe this properly in english .

btw i think the method described by Francis doesn't work when you place the horizon line in 3d-view higher above your cube, because the front egde will appear actually shorter in perspective than it is in the top view, won't it? there is another way of "projecting a shape" (grammar? is this english?) using the top and side view of your shape and the hight of the observer, but i'm not quite sure right now how it was done.

[Prometheus-ANJ]

Here is a cube pic I made. I didn't read all of spooge's text so I might have missed out some things (I was too eager to draw). Anyway I already made the pic so I'm gonna post it here anyway. If someone can spot any obvios errors, let me know.

Things I had in mind while drawing this pic:

- Primary light. Things closer to this lightsource are brighter (I forgot about this when doing the pic tho...).

- Ambient light makes shadows less dark, can be 'colored' light.

- Light bounce around causing radiosity (3d term). This means that the table (white ground plane) casts white light at the bottom of the cubes. The cubes also cast light on the table and on each other.

- White surfaces shine a little causing diffuse flares, sometimes.

- Atmospheric perspective, ie. things get darker and loose contrast the further away they are from the EotB.

- All surfaces are more or less reflective.

- Shadows get more and more diffuse (and thus brighter) the further away they are from the 'casting object'.

Pic will load here:

http://home.swipnet.se/zebes/img/anj77_cubes.jpg

[spooge demon]

The cast:

Bg
CyBeAr
Dean Welsh
Horstenpeter
Lel
Mime
Morphgfx
Nil900
Prolix
Ripelly
S4Sb
Shawncollette
Silber
Slicer
Tiger Eaten


The /incoming directory is only visible to me. Your files are coming through fine.

Here is the page for the first assignment. You can see who is there and who is� slacking.

I will do the first crits this weekend. Please have your drawings ready by then.

Lighting can be either natural or artificial. Natural light is preferred, as it is less prone to making bizarre shapes and distortions of shadow patterns. Non-ambiguous, quick and clear reading of form is what we are after. Neat little tricks of light and flares and that kind of thing should be avoided. That will come later.

You can do these digitally or traditionally or a combination. 3-d would be a little self-defeating, though. But you can use 3-d as a study, just like real cubes.

Aspect ratio of 3-2 just means that whatever the width is, the height must be 66% of that. I think� So you can work at higher rez and then scale down to 600*400 with no problem

I first did this with charcoal on charcoal paper. You ground up the charcoal by rubbing it on some scratch paper till you had a pile of extremely fine charcoal.

You then mixed it with baby powder to dilute it. You then used nonstick tape to mask the area to be worked. EVERYTHING else had to be covered. Then you used a lithographers pad to spread the charcoal baby powder mix onto the surface. The baby powder filled in the surface of the paper and allowed you to slowly build up a gradation. When the paper's tooth was filled, you sprayed some fixative on the paper and that gave it some tooth again. Back to another coat of charcoal. Sometime you could repeat this process 10 times. And the fun part was you could not see the rest of the drawing, so you could not compare values. You quickly learned the value of accurate roughs.

The paper was amazingly unforgiving. It showed the slightest imperfection or prior fingerprint. It was time consuming. A good example could take 15-20 hours. And the slightest slip up at hour 19 is disaster. For example, if the fixative had a little buildup and spit a little on the paper, you are done.

This was an immensely cruel way of starting out at school. But since the beginning ACCD students had egos the size of the western hemisphere (the biggest and best hemisphere, I might add something like this was need to wear them down and shoehorn some knowledge into them.


I have mirrored the cubes PSD elsewhere, as some had problems with it.

Some found errors in my drawing, how embarrassing! Yes there are a couple of inaccuracies. The version that is up now is better. Good eye, boy scout.

[Sumaleth]

Morph:

Last time we did this exercise we did try to find out some mathematics behind this sort of perspective, but no one seemed to find anything. There probably is some, but I think that this apporach to 2D perspective is very much an appoximation - it's not "real" perspective.

So we never found another way to find the vanishing-points for the second cube except with top-down projection.

The angle-of-view is determined by the distance you place the "eye" from the "image plane" (really close is like a wide angle lens and far away is like a telephoto lens). Close will put the VP's close together and far away will spread the VP's wider apart. But because we're treating the horizon is a simple line, the distance between VP's changes depending on the objects rotation - we really need to think of the HL as a *circle* around the camera for it to work, but thats where we need the math.

I'd be interested to hear or any other methods for drawing correct perspective with multiple vanishing points though.

(I don't know why I'm so fascinated..)

Row.

[ October 16, 2001: Message edited by: Sumaleth ]

[silber]

@sumaleth:
they are just awesome man
question: I used the channels in PS to mask the cube areas and painted on the RGB channel.But why use the channels? Actually I could also have used layers for this.
I know that channels can be advance in other cases....but for this?hmmmmm
maybe I missed something.

@ANJ-77 : you should consider reading spooges text otherwise you will miss the whole thing behind this lesson.

[ October 16, 2001: Message edited by: silber ]

[Sumaleth]

Silber:

I've never actually used channels so I can't say how good they'd be for this sort of thing (they might be perfect), but I used layers - one layer with matte channel per "face" and per "shadow".

Row.

[horstenpeter]

Here is what I also sent to spooge. I'm not too happy with my light source since it makes the two sides closest to it almost equal in value. Also, the shadows are too extreme with a lightsource that close. I'm not sure whether I'll find the time to do a new one though.

spooge, you should have 2 versions of my image. I just antialiased the edges in the second one. No need to post the first one. Looking forward to hear your comments, and thanks for doing this !

[morphgfx]

@Sumaleth:
thanks for your help again ! this is realy interesting. acutally its kinda frustrating that there isn't any cool secret method how to do it though . i'll keep researching...

[Bg]

Just in case the pic didn't come through...

[Dean Welsh]

Howzzat?

-Dean

[Anthony]

Looks good Dean - the shadow on the face on the right cube would be a different shade than the shadow on the ground in the back though right? That would help seperate the two, make it more readable. Good job peeps! ME gotta do another one, not so funky this time.

[silber]

hmmm did I miss a thing?
Did everybody (the cast) send his/her picture to spooge?
Or is spooge just very busy?
I'm not impatient I'm just curious.

[S4Sb]

I think everybody sent it in... he's just busy as usually

[jHof]

How do you know how far back the shadows will stretch? I'm going bonkers... I DownLoaded the cube1.psd, but I don't understand how to calculate/measure/line-up the shadow lines...

Not asking for The Spooge himself to answer, but anyone that is familure with this process.

Thanks =) Hope he's still planning on work'n on these with people.

*GulP* Help :|

[ October 31, 2001: Message edited by: jHof ]

[ October 31, 2001: Message edited by: jHof ]

[Sumaleth]

Francis's site also includes a tute on adding the shadow. Essentially you place the light in the scene.

Then project lines from the light position, through the top corners of the cube, and onto the ground. To work out where the ground is for each of those projections you draw some more projections from a point on the ground directly under the light, through the lower corners of the cube, and out to where they intersect the previous projections.

Might sound confusing, but if you check Francis's diagrams you should be able to see whats going on.

--

Also, on your other problem; draw some lines on the top view of the cube that run parallel to the sides of the cube, them slide them (on a different layer) into position. Don't try to eye it, you'll be off (as you are in your current image).

If you still can't make sense of it just say.

Row.

[grimsheep]

Spooge, I think its great that you are doing this... especially for the people who are doing 3d work right off the bat and heve never really had to think about this type of thing from this perspective(no pun intended )

I did this exercise too in my first year; was only mildly painful. They were sticklers for the proper calculation of perspective and the cast of the shadows but we weren't subjected to 20hr crushed charcoal renderings,just noxious marker fumes

[n8]

umm...just a quick question. Imagine the box was like a cardboard box or sumthing...whats the shadow look like if you have the lid open at the top??..

[klaivu]

too late ?

[ November 02, 2001: Message edited by: klaivu ]

[Sumaleth]

n8:

You'd just need to find where the two new points project to;

First you'd draw two vertical lines, one from each of the new corners straight down.

Then continue the lower edges of the box out until they intersect with those vertical lines - now you know the point on the floor directly below the new corners.

And then just project the light constructions lights for the two new corners. Ie. just the same as the rest of the box.

Row.

[jHof]

Do you guys use the "Polygonal Lasso Tool" in Adobe to make these boxs?? Or do you all draw out all the perspective lines, then erase them later?

[Sumaleth]

I made a separate layer for every plane, using a mask to create the shape. So it was easy to use big airbrush strokes to lay in the shading.

Row.

[spooge demon]

cubes excercise

Is up.

many thanks to Sumaleth for helping me out with editing and formatting. it is a much stronger thing now.

Find the link to the first assignment on the above linked page.

[silber]

hey thanks spooge and sumaleth

quote: "Good control and workmanship. Turn on anti aliasing with your selection tool? "

hmm sorry maybe it's my english but do spooge meant I should turn on anti aliasing or was that a question if I turned on the anti alaising tool?

-some nativ american know?

[Anthony]

Silber - yeah, he meant turn on antialiasing on the tools(like the line tool). He wasn't sure that's what the problem was, so he formed it as a question. Thanks Spooge, Sumaleth!

[jHof]

Sumaleth -- Ah, thanks for the reply. Guess I need a few tutorials on masking. I've known the term, but never knew how to utilize what it does.

Spooge -- Much thanks for staying on this form lesson with all of us. I hope it continues when it can.

[Mime]

Thanxs a lot for the time you spent on this Spooge, it is really helping

about your last comment on my cubes, since i have some english problems sometimes, i am not sure of the meaning
I guess you mean that i should have made one of the shadows overlap the other cube, am i right ?

What do we do now, we try to correct the mistakes and send the second version at the same FTP ?

or do we try to start the second exercise ?

thanxs again

[horstenpeter]

Hey spooge, thanks from my side as well. I really feel like I'm learning something. And that's always fun

So right now I have the same questions as Mime, what's next ? I think I'll do it again, just because I think that might help internalize the things that can be learned from this exercise.