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ASSOCIATED FILES: Terrain and World File in ZIP format

How to woo your audience with lightrays - OK - stop getting giddy and concentrate.

Like my texture tips guide, This is not intended as a tutorial, but a brief guide on Lightrays. I am also assuming the intended audience has some knowledge of Terragen. If you need guidance on starting out in Terragen, try the tutorial by Carol Brooksbank at http://caroluk2.crosswinds.net/terratut/

QUICK AND DIRTY SOLUTION - A guarranteed ray producer:

1. Load terragen ( I'm using v0.9.08 ) without any additional files
2. in the sun dialog, set sun altitude to 15, heading to 0 and 'clouds cast shadows' to on
3. In the clouds dialog, change sky size to 10,000 and altitude to 500
4. in the rendering dialog, change camera heading to 0.
5. render preview.

If you don't immediately get rays, then your sun isn't being blocked by the clouds, rectify this by either adjusting the sun height and heading or increase the cloud shift value.

Now on with the guide, the following will attempt to clarify why those quick 5 steps got you those rays..

There are three dialogs in Terragen I will be looking at in this, the Cloudscape, Atmosphere and Lighting Conditions.

You might want to load the world file and terrain at this stage so you can follow my steps.

Atmosphere

The common error in attempting to get lightrays is to think that haze is the culprit - it isn't directly related but will really only have an good effect on rays coming in from the side of the scene or over the tops of the mountians, so use this dialog only to get your colouration of the sky. For this guide - I have virtually no haze setup (Thats essentially the density) and my half-heights are reasonably close to the defaults.

Lighting Conditions

We are only going to look at the first tab in this dialog.

The "Direct Sunlight" one, the checkbox "Clouds Casts Shadows" needs to be checked for rays to work.

The Sunlight strength will also have a big impact - becasue you will be placing your sun partly behind clouds (I'll come back to that), your sunlight needs to be quite powerful, the lower down in the sky the brighter it sould be. For my example, a 1600% strength ensures the beams will reach the ground.

The only other part of this dialog is the position of the sun - I will refer to this when I explain about the clouds.

Cloudscape

This is the most important dialog where lightrays are concerned.

I will try and use a torch as an expample - place a torch on the table and aim the light beam onto a wall, than put your fingers close to the torch - you will cast a shadow on the wall, now move your hand towards the wall, your finger shadow will blur - This is the same with the clouds - the higher the altitude the better the rays - this does have a downside in that you will need a large sky for this.

Cloud Generation

Lets generate some clouds - select the "Generate Clouds" button and select a cloud size 3 to 4 notches away from the max setting and select a Persistence of about 34 (persistence determines how many smaller clouds are generated around the larger clouds).

Altitude

Set your altitude to be around 300 - 500 - the higher the better, but bear in mind that your sky will need to grow for this. (if you get to a point where your sky is 10000 and your clouds are not high enough, adjust your terrain height in the Bound vertical part of the modify terrain settings from say -20 to +80 will then become -40 to +60)

Depth/Thickness

The thickness of the cloud does not really bear any relation to the rays - use this to get your glouds looking real it can be as low as two but, the higher the number, the better the rays are defined, use 6 or higher for a better result.

3D clouds

Use only for cloud realism - again - this doesn't affect rays

Darkening

Another setting which won't stop rays - the darker the better though, as your rays will stand out more agains darker clouds.

Density Contrast

This is probably the most important one for definition of the rays - the higher the contrast, the sharper the edge of the cloud - think back to your torch, this will simulate the edges of your fingers, if you yous cotton wool instead of fingers, don't expect rays, you need well defined edges, so in this case, the higher the contrast setting, the better the definition of the ray. There is a downside to this though, your clouds will start to look like cardboard with this setting too high.

Density shift

This and your generate clouds button will drive you made for sure - Once you have generated some clouds, use this to increase or descrease the quantity of cloud cover. What you should be aiming for is a hole in the clouds where you want your sun to come through.

SUN POSITION

This last part is the most crucial part. It is no good trying to think about getting rays if your sun is in full view. You need to hide behind the clouds. Depending on where you want your rays, depends on position. I like to see some part of my terrain in sunlight when I do the scenes, so I try and get a tiny piece of sun to peep out from the edge of a cloud. The most dramatic rays are usually produced if the sun peeks out from the bottom of a cloud.

Use your "Lighting Conditions" dialog box to adjust the placement of the sun - the pic on the left denotes the direction of the sun toward the centre of your map and the picture itself shows the shadows it will create on your map. The pic on the right is the height of the sun in the sky.

Have a play around with the sample files and don't forget to let me know if you found this guide useful.

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