I had previous experience using similar programs (VistaPro for the PC, in particular), but this was my first major experiment with Terragen.

Default, Earth-Like Image:

Using the default coloring, atmospheric, and cloud settings, I came up with a pleasant, realistic scene (for Earth, that is.)

First Attempt to Simulate Venus:

Next, I increased the cloud cover, and adjusted all the colors.  I also positioned the sun a bit higher in the sky and to the right, to get a bit more highlighting on the foreground rock.

This certainly feels hot, but much too bright.  And although a bit hazy around the sun, the effect on the rocks is of direct sunlight, not at all realistic for Venus.

Eliminating the Direct Sunlight:

For this image, the only setting changed was in having the clouds cast shadows.   In other words, the cloud cover has influence now on the lighting of the terrain.   With such heavy cloud cover, the land is in shadow.

This certainly feels overcast, but I felt that it lacked the sense of heat I wanted.

Adding More Haze, and Strengthening the Sky Color:

To create more of a sense of heat, I increased the amount of haze.

I thought also that adding more chroma to the sky would intensify the oppressiveness of the atmosphere.

Removing the Atmosphere:

Since I wanted to bring out some highlights in the foreground rocks, I decided to see what the scene would look like with the atmosphere removed completely.

I guess this is a scene on Mercury.

Compositing Various Versions:

This image is a complex composite of a number of the above images, placed on various layers in Photoshop.

I still felt that the sun was too direct - it needed to have a bit more cloud in front of it. And I thought the sky now had too much color.

Final Composite:

I took a bit of cloud from one of the images and placed it over the sun.  Some of the compositing techniques I used created the hint of a halo around the sun, and then the bright area beneath the sun cried out for a few rays scattering down.

I darkened the upper left corner of the sky, and the bright sky area over the right-hand rocks.