View Full Version : Conical flask help

04-07-2004, 09:48 AM
Hi everyone,

I've worked near-solidly for three days trying to model and render an empty conical flask (made out of glass) on a plain white 'floor'. Attached is what I've got.

It doesn't look that realistic, in particular the shadow isn't right, the top of the flask looks like white plastic, and the floor is grey!

Suggestions as to how I could improve it would be very much appreciated!




04-07-2004, 10:41 AM
are you tring to get it to lokk real? It looks like there are no fracting in the shadow edges should be softer. Try using two lights softer looks a little bright.

does the flask have thinkness I dont see the back?

04-07-2004, 11:12 AM


04-07-2004, 11:41 AM
Hey, there are a few problems with your flask render, but the important one is the fact that the refraction is wacky. I'm fairly new to the Lightwave application, so I'm not sure exactly what controls you get, but currently it is rendering as if everything behind the front surface of the flask is solid glass, as opposed to only 3mm of glass, then air, then 3 mm of glass on the back surface, and then air again, so everything is much too distorted, and you're missing out on some really great edge effects that you get where the surface normal starts to go perpendicular to your look vector.
Not sure if Lightwave lets you do multiple "bounce" refraction, but if it does, you need at least 4 to get a flask to look right (one for each transition of medium).

It will also read better as glass if you turn caustics on, and if you have a stronger environment to reflect.

The rest is just aesthetic stuff you can tweak (higher contrast image, blurrier shadow, etc., etc.).

04-07-2004, 05:44 PM
Thanks for the replies. Here's what I came up with. However, I am not sure how to blur the shadow. Rendering with radiosity turned on also takes too long (I gave up waiting - this is on a 1.7 GHz Pentium 4) - is it important?


Also I don't quite get the thing with making the "air" polygon. I copied the procedure out of the PDF linked above, but my flask was modelled with sides of finite thickness - so now surely I have an infinitesimally thin glass flask whose sides are separated by air? Since when I created the air polygon I copied and pasted ALL the polygons and not just the ones that face the inside of the flask?



04-07-2004, 06:52 PM
The air polygons are flipped inwards so that when you're looking through the glass, you're seeing the outside of the surface you're looking directly at and then you're seeing the air polygons on the far side of the glass(inside) which is now facing you. I think that's what you're asking about.

04-08-2004, 03:21 AM
Sorry about it, but I got kinda obsessed with your project. I also made a conical flask and rendered it. :)

You were asking if radiosity is really that important. Well, in my opinion it is(or you should use caustics instead).

Long render times were also a problem for me, but not anymore! The solution? Fprime ofcourse!

For example, this render took me about 5 minutes:

This render has 5 bounces of ray-recursion and it's Monte Carlo radiosity. I used a HDR as Image World(If you want to know how to do this, just say so).

Btw: Such a conical flask is called an Erlenmeyer.

04-08-2004, 05:35 AM
Joppe, that shadow is pretty incredible! Was the HDRI image your only source of light?

04-08-2004, 05:38 AM
No, I used an additional spotlight to get that shadow.

Thanks for the positive comment btw!

04-08-2004, 05:51 AM
thanks, hrgiger, I think I see what you're getting at.

Joppe, it looks fantastic - please can you explain or direct me to more information on what you mean by "I used a HDR as Image World"?



04-08-2004, 06:09 AM
I thought this tutorial covered it.

Proper HDRI Lighting (http://www.dbki.de/tutorials/eng/hdr_lighting/index.htm) (Also some other useful tutorials on this site)

If you still have questions I'll gladly hear them.

04-13-2004, 06:53 PM
Umm...still not totally sure (I did read the stuff you linked to!) - this is a way of using an image to generate a shadow? My shadow is totally uniform - looks wrong.

How do I supply the image to Lightwave, and can you send me the image you used for your conical flask?

Here's the flask as it is now:




04-13-2004, 08:04 PM
Problems with the hdri... Let's solve 'em!

First you'll need the image which you can find here:HDRI (http://www.dbki.de/tutorials/eng/hdr_lighting/pic/hdr.jpg)
The next thing to do, is to load the image with Lightwave's image editor. Now we just need to set this image as our imageworld. This can be done by pressing [Ctrl]+[F5] where you can add Image World as an environment. Here you can slelect the image you just loaded. That's about it.

EDIT: Proper link for HDRI

04-14-2004, 07:04 AM
Thanks, I got that to work. Have adjusted the lights a bit, too. But the top of the flask looks like plastic and the shadow isn't right - do I need to activate radiosity?




04-14-2004, 07:20 AM
Are you sure your Shadow Type is set to Ray Trace?
When I set this option to shadow map I also got a faulty shadow.

Guess FPrime always raytraces shadows...

About the top of your Erlenmeyer looking like plastic. I think that's because you overlighted it a bit, just adjust your Light Intensity.

04-14-2004, 12:50 PM

It's definitely set to Ray Trace.

Maybe this is the best I can do without FPrime?



04-14-2004, 01:03 PM
No, Fprime isn't going to give you a BETTER render than LightWave. You just don't have things set up the same as Joppe did.

You should sweet talk him into sending you his scene so you can see exactly what he did.

04-15-2004, 06:39 PM
He said he was using FPrime. Joppe, can you show us what your scene looks like without FPrime?



04-16-2004, 12:56 PM
my guess is you don't have caustics on.

04-16-2004, 05:26 PM

What you're missing out on is the Fresnel effect, briefly described
here (http://www.graphics.cornell.edu/~westin/fresnel.html). What you need to know though is simply that a surface is more reflective to light at a glancing angle than light hitting it front on. The result is that on your flask the shadows should be darker around the edges (roughly) like in Joppe's image.

The good news is you don't need FPrime, you can do it all in LW, the quick way is to go to the Shaders tab in the surface editor and apply the Fast Fresnel shader. Alternatively you can apply suitable gradients to the various surface attributes.

Hope that helps,


04-17-2004, 08:04 AM
Caustics and Fast Freshnel are already on...?

Also, what's causing the weird 'U'-shaped grey line on the walls of the flask facing the camera?



04-18-2004, 06:06 PM
I've got a question about HDRI images - what makes a good HDRI image to use? I.e. can I use any image for HDRI? And does anyone one know a good place on the Internet to download appropriate ones?



04-19-2004, 12:29 PM
Originally posted by mattclary
No, Fprime isn't going to give you a BETTER render than LightWave. You just don't have things set up the same as Joppe did.
You should sweet talk him into sending you his scene so you can see exactly what he did.
This proves it:
This image was created without FPrime.

Here's the model and the scene to solve your remaining questions, rtg20: Erlenmeyer.zip (http://www.fmf.nl/~sietze/Forum/Erlenmeyer.zip)

When I was trying to render the scene with Lightwave's renderer, I also tried to get some caustics in it. I had some problems doing this. To get a visible caustic effect, I had to raise the caustic intensity very high(500-1000%). Finally with caustics visible I got some strange reflections:

Since I already put my scene online maybe you guys could take a look at it this problem :).
Thanks in advance.

04-19-2004, 01:00 PM
Originally posted by Joppe_Bakke
Since I already put my scene online maybe you guys could take a look at it this problem :).
Thanks in advance.

Probably not neccesary, I've run into the same flaky issues with caustics in the past. Have to jack them waaayyyyy up to get any kind of effect.

04-19-2004, 01:19 PM
That's a relieve!

Next project! :D