View Full Version : Slope Problem

11-30-2011, 04:05 PM
I use gradient slope alot to surface topo models, and generally the parameter of 0 applies to the flat, 0.5 to a 45 degrees slope, and 1.0 to a vertical ... whatever the actual maths of Slope, that's how it seems.

I have this topo model that I'm working with now but it's not behaving as I expect.

With the gradient slope, the 0.0 parameter colours the flatter areas, but although there are some ridges with slopes around 45 degrees and more and I'd expect them to be coloured according to the slope's 0.5 parameter, they are actually taking their colour from around 0.01, with the steepest sections coloured from about 0.1.

I don't get why this is, but it's meaning also that the gradations are pretty hard and I'm not getting the smooth transitions I need.

It's worked well enough in the past, and I just tried it with some simpler objects, on which it worked fine, so does anyone have any ideas why this mesh should behave differently?



12-10-2011, 05:19 AM
Well, I can't figure what the devil is going on here. I've built test slopes in the meantime and they work normally, though they are smaller meshes, in linear measure.

I can only wonder if the large scale of this mesh relative to the slopes, which are just made up of small handfuls of polys, is not the culprit.

Don't know why, but then I don't develop this stuff ...


12-10-2011, 06:03 AM
Share the object?
Couldn't it be the Gamma correction?


12-10-2011, 07:50 AM
Here's the object that's shown in that screengrab. It's a section from a much larger topo mesh, around 822,000 quads, 169m x 418m x 2.2m (X,Z,Y).

I don't see how it's related to Gamma correction ... I'm trying to apply variations of colour and shade with Gradients using Slope.

The behaviour I normally see using gradient slopes is not what I'm seeing here ... unless I misunderstand how gradient slopes actually work. Someone some time ago posted about this, saying that it's not strictly the angle of the slope of the mesh, even though it kind of looks like that's what's happening, ie. 0 is flat, 1 is vertical.

Here, even the steepest slopes, which are greater than 45 degrees and therefore should be coloured with the slope value around 0.5, actually get colour from around the gradient slopes' 0.002 value; on many other meshes, that would be flat, near enough.

I still think the low Y values of the mesh, relative to the X and Z dimensions may have something to do with it ... well, except with this cutout section that doesn't apply, though it still displays this problem ...


12-10-2011, 09:09 AM
Julian, in the attachment I used a Curve Node to modulate the Slop Gradient. Since the geometry you have there is no sphere it will not behave like Slope behaves in a shpere, linearly. You have to bend it, so it becomes more linear according to your geometry. Hece my confusion with Gamma, since this is somewhat a similar operation, I guess.

First Curve Node is to try to make the gradient linear, second one is to lift some values and the last gradient is just to make the colors.

I guess that with your 800K model, the render will look smoother.

Hope this is it.


12-10-2011, 12:41 PM
That's great - thanks very much! This approach makes alot of sense, and also highlights that my perception of Slope was somewhat off.

This is giving better and more controlled results now, so again, many thanks!