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LearningLightW
08-26-2008, 02:55 PM
Hi, does anyone have experience using LightGen2LW? I'm having difficulty casting shadows into my scene that is lit by an HDRI image. Here is what I did step by step:

1. I created an inverted sphere to act as my globe and textured it with a spherical map HDRI with a Width and Height Wrap amount of 1, although I read some tutorials that recommend setting those to 3.

2. I rendered the scene with my camera close to the middle of my sphere (does the position of the camera matter?) and saved the image as a bmp.

3. I created a plane and textured it with the image as a front projection and set the plane in my globe to act as my ground. Then I put a small sphere on top of the plane.

4. Using HDRShop and LightGen2LW, I created an x amount of directional lights to light my scene. Tutorials I've read said to create 10-20 lights, but does it make sense to create that many? I thought the purpose of LightGen2LW was to simulate the sunlight and leave the ambient lighting to the HDRI image itself? I would think only 1 light is enough.

5. Anyway, I cannot get the shadow casted by the small sphere to look right. I circled in red shadows from the HDRI of small pebbles. Notice how they are kind of cast to the side. But my small sphere's shadow looks as if the light is directly on top of it, where as it should look like the light is coming from behind the camera to match the pebbles' shadows.

any help would be appreciated!

MooseDog
08-26-2008, 03:33 PM
a light dome like you created mimics all the bounced light rays that surround us outside. you'll still need a key light to mimic the stronger direct rays of the sun. this way you can place it right where you want so the shadow from your sphere falls in the correct direction. should do the trick:thumbsup:

LearningLightW
08-27-2008, 08:52 AM
is that key light placed by me or lightGen2LW?

MooseDog
08-27-2008, 09:41 AM
you :). i don't know where you're coming from needless to say, but maybe a good exercise in lighting might be, in a fresh scene, set up a three light system on some random object, or a four light system. google the terms and start spinning the knobs in lw!

Paul Brunson
08-27-2008, 10:31 AM
Yes you should place the light. If that's all you're looking to do is have a light representing the sun, casting a shadow

I think you may be confusing the purpose of Lightgen. Lightgen creates a array of lights meant to approximate the light coming from the HDR dome. It was intended to create a faster rendering alternative to lighting with an HDR Image. If you're going to continue to use the HDR image for lighting in your scene as you mention, then its redundant to use lightgen. Just use the image wrapped to the dome object or to LW's BG (Lightworld plugin or texture environment plugin) and a directional light for the sun and place it where the sun is in your image.

Granted you can technically have lightgen generate an array of lights for you and then sort through the lights looking for the one Lightgen used to represent the sun, but its faster and quicker to just place the sunlight yourself.

Again the purpose of Lightgen is to create an array of lights that approximates the lighting coming from an HDR image. If you're going to use the HDR image to light the scene there is no point in using Lightgen. And honestly with Lightwave's radiosity getting as speedy as it is these days your likely better off using radiosity and the HDR Image instead of Lightgen anyway.

LearningLightW
08-27-2008, 10:35 AM
thanks for clearing that up!

inakito
10-08-2008, 08:47 AM
Yes this is true tho!
If you are thinking in using Lightgen you need to think any radiosity will be used for the lighting. The idea behing Lightgen is recreating the dome you have in mind to use for your scene using as many lights as you specify( white dots in your text file created from hdrshop).
If the HDRI is good enough there may be a light precreated by Lightgen that is much more intense that the rest, making it the sun.

This plugin is out of date anyway so I may recommend you the use of LightBitch that is freeware aswell.

Hope it helps,

Thanks

MooseDog
10-08-2008, 11:03 AM
i may be wrong, but i believe lightbitch is "nagware". i.e. if you don't have a magic keyword taken from the book, the program will nag you for a purchase of some sort.

i say i believe, because i purchased the book:

Amazon - HDRI Handbook (http://www.amazon.com/HDRIHandbook-Dynamic-Imaging-Photographers-Artists/dp/1933952059/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1223485241&sr=1-1)

extraordinary resource :rock:, worth every penny!