A gracious request for a little guidance

[Kokosing]

Hello Terragen Wizards!

This is my first post here. And, if I can figure a few TG basics out, I hope to start hanging out here regularly. 

I'm completely new to TG, but not entirely new to 3D environment creation and rendering. I've been making animated maps for a few years. Stuff like this: http://vimeo.com/19713691

I've wanted to add Terragen to my toolbox for quite a while, but I'm finally getting into it now because I really need it. 

I need to build a realistic environment around an ancient historical site. Being a Neolithic site, the geography around the structure is very specific. Unfortunately there's very little data available about the area. The SRTM data is 90m and full of holes/anomalies. The satellite imagery I've found is of poor quality and full of clouds. 

I've found some decent aerial photos and done my best to rectify them and draw some contours.  I've managed to build up a 4 level grayscale image which I'd like to use as a starting point. 

Ideally I'd like to bring this into Terragen and then use the controls there to add more surface detail and possibly colours. Then I'd want to export the terrain and colours so I could use them in my comfort zone of Cinema 4D and Vray. 

If I understand correctly, I'd export my terrain as either an EXR or a LWS. I'm happy to use either. But it looks like the LWS can only be created from a heightfield and not further down the node-tree after I've added displacement. I also see that to get colours out I'll need to render a top view without shadows or atmos.

Here are some issues I'm having which I can't seem to find answers for:

Should I bring in my handmade grayscale as a heightfield or as an image shader with displacement? Is there a difference?

I can't seem to limit additional displacement to an altitude or slope. I've added a surface shader and can limit it's colour based on slope (it doesn't seem to care about altitude) but I can't seem to get any displacement without affecting all altitudes or slope angles. 

Could anyone point me to a tutorial or documentation for this workflow? It appears from the description on the TG2 website that this is an intended use for the software. But I can't seem to find much info on how to do it. 

Thanks very much for any advice. I really appreciate it. 

W

[Pentagular Dark]

Did you try making the displacement a child layer and turning off apply displacement?

[Matt]

If I understand correctly, I'd export my terrain as either an EXR or a LWS. I'm happy to use either. But it looks like the LWS can only be created from a heightfield and not further down the node-tree after I've added displacement. I also see that to get colours out I'll need to render a top view without shadows or atmos.

You can generate a heightfield from displacement shaders using a Heightfield Generate node (it has a built-in fractal but is overridden by any shader you plug into it). You could generate new heightfields that represents your terrain after additional displacements.

Here are some issues I'm having which I can't seem to find answers for:

Should I bring in my handmade grayscale as a heightfield or as an image shader with displacement? Is there a difference?

With Heightfields you can make use of heightfield operators such as erosion etc. if you want them. They can be positioned using lat-long coordinates. The Heightfield Shader has built-in fractal detail (which can be disabled or adjusted) which is unique to that Shader and might be difficult to duplicate with other shaders. Heightfield Shader is easier to merge with adjacent heightfield shaders if you have multiple tiles.

The Image Map Shader has a bug which means you have to check "data is linear" on both the colour tab and the displacement tab. The bug is that the option on the colour tab affects both colour and displacement, a problem which is easy to overlook.

The Image Map Shader has some advantages over the Heightfield Shader. It can be repeated (tiled). It can be warped by the Warp Shader and transformed by the Transform Shader. Therefore it can be rotated, which is not currently possible with a heightfield. Different projection modes are possible, whereas the Heightfield Shader is more limited.

I can't seem to limit additional displacement to an altitude or slope. I've added a surface shader and can limit it's colour based on slope (it doesn't seem to care about altitude) but I can't seem to get any displacement without affecting all altitudes or slope angles.

To get a displacement to know about slope, you need to put a Compute Normal node or a Compute Terrain node (which also computes the normal) somewhere upstream. One way to do this is to put your additional displacement after the Compute Terrain node which already exists. The advantage of having only one Compute Terrain node is that you don't compound the calculations needed to compute the normal, which makes computing upstream nodes take about 3x as long. The disadvantage is that surface shaders following the displacement won't be fully aware of the additional displacement. They will be aware when applyingn colour and shade, but not further displacement (you would need yet another Compute Normal or compute terrain then).

Further reading on Compute Terrain and Compute Normal:

http://forums.planetside.co.uk/index.php?topic=1249.msg12539#msg12539

Matt

[Kokosing]

Thanks Catfish.  I was missing that.

And Matt, thanks a million.  I'm much closer now.  And I have a much clearer understanding of some key points.  I'm sure I'll have some follow up questions.  But I've got plenty to chew on right now.

Cheers!

W

[rcallicotte]

Yeah, thanks Matt.  Your explanations always make things so much clearer.