Join Josh Modglin for an in-depth discussion in this video Grading criteria sets, part of AutoCAD Civil 3D Essential Training.
- [Instructor] Whenever we begin to grade, we may in our mind play out a lot of different criteria and scenarios that we don't even realize. It's like riding a bike. If you start trying to think about what you're doing, it almost becomes hard for you to do. But we've learned how to do this grading because ultimately in our minds we always have a base we're working from. Some type of base point elevation starting point. Then from that point, we answer two questions in our mind.
We're answering where are we going and how are we going to get there? So let's look at this cross section we see here. It's a pond cross section. We're coming from the bottom of the pond and so there's our base point. We have the bottom of our pond. Where are we going? We are going to an absolute elevation of 737. Well how are you going to get there from the bottom of the pond? We're going to go at a slope of 3:1. Once we get to the elevation 737, where are we going? Well in this case we're going at a distance of three feet.
Well how are we going to get there? Well it's going to be pretty flat. We want some positive drainage into the pond. But it's pretty flat. Once we get to the edge of our ledge here, where are we going then? We're going to an absolute elevation of 740. How are we going to get there? 3:1 and you see how these two questions come into play. You have a base point that you're starting from and then two questions you have to answer. Again, we do this in our minds. We don't even realize we're asking or answering these two questions. This is how Civil 3D grades for us.
All we have to do is provide those three criteria. We have provide a starting point. And that's a feature line. Feature lines of course we covered in Chapter 12. We have to provide it the criteria of where we're going and how we're going to get there. And so all of that information is stored in what's called a grading criteria. And just like with parts lists in a pipe network, criteria is stored in a collection or a set. Let's see how we have that in our drawings here.
So as we go to our Civil 3D, we're going to open up our exercise file 13_01_GradingCriteriaSets and we're going to create a grading criteria set within this drawing. So from our tool space under Settings, we find Grading, we expand that out, and Grading Criteria Sets work like styles and so they're stored within the drawing. We already have one. We're going to create another. So we're going to right click, create a new criteria set. And since this is just a collection, we just name that collection.
That's pretty much the only property here. Of course, give it a good description. We click OK and we have the beginning of our criteria set. Now if you recall at the beginning of this exercise, what we talked about was we're coming from the bottom of the pond and we're going to an absolute elevation. We're getting there through a slope of 3:1. So let's create that criteria. I'm going to right-click and choose new. So in this case, we're going to name our criteria 3:1 To Elevation.
Of course you can give a good description, explain it a little bit more if you'd like. Now the criteria tab is where we find the answer to those two questions. Where are we going? This is our target. And we could be going a distance of. We could be going to the existing grade. We can be going to a relative elevation five feet from our current location. Or in this case, an absolute elevation is where we're going. Now we mentioned that we're going to an absolute elevation to get from the bottom of the pond to our ledge.
But we're also going at 3:1 to another elevation to get to the top of our pond. And so because we have both scenarios where this criteria would work we're going to leave the elevation value of zero and leave it unlocked. This gives us the ability to be prompted for the elevation when we use this criteria. We did name our criteria 3:1, so we're going to lock that. We don't want to be prompted for this information. So these locks don't mean that we can't unlock these settings in the criteria and change our style.
What we're really doing is we're defining what can be edited. What is being prompted as well as what could be edited later for this criteria. Lastly, when we're grading and we have a feature line we're coming from. Let's say the feature line has an arc. And the radius of the arc is five feet. But as we grade, we're coming inside and we're passing the center point of that arc because our grades coming from both segments, we have to grade down eight feet.
When we do that and we pass the center point of our arc, and we've now taken two elevation points that may be at different elevations and we're combining them into one. Now trying to deal with that overlap and the resolution of how we deal with those elevations that we're now combining from two elevations into one, how do you want to deal with it? And so what is normally the case is we use an average slope. The difference between the two elevations and then average it out.
So it may not be perfectly 3:1 in these interior corners, but that's okay. That's how they would of course grade it on sight as well. So we're going to lock all of these so the only thing we'll be prompted for is to enter the elevation. And that way we can use this in a versatile way. So really this one criteria took care of two scenarios that we saw in our presentation earlier. The next criteria we need is to deal with our little ledge. That three foot wide ledge, even if you noticed our eight foot berm at the top of our pond.
Let's right-click and add a new criteria to deal with that. In our information section, we're going to name this Flat Shoulder. You can give it a different name if you'd like. But that just really helps us define how we're going to use that criteria. Where are we going? In this case we're going a specific distance. Now again, we can use this same criteria, not only for that ledge inside our pond but also for the top of our pond, our berm.
And so those are going to have differing distances. So we will leave them unlocked so as to work with them. However, it's really trying to identify when it goes this distance, how is it going to get there? Now besides the fact that we've named it Flat, we are going to give it a little bit of a grade or a positive drainage into the pond. So in this case we're going to change our format from slope to grade. When we did that, notice our values changed, ambient settings. And we're just going to type in two here for 2%.
Since we named it Flat Shoulder, we don't want to be prompted for this. We already talked about dealing with the interior corner overlap as well. So again, with this criteria, the only thing we're going to be prompted for is the distance. And so we click okay. So with four different scenarios with building our pond, we've been able to address them using two criteria. The last criteria that we really need is daylighting to our existing grade. So again, answer those two questions. Where are we going? We're going to an existing grade surface.
How are we going to get there? At an elevation of 3:1. So we're going to create one more criteria. We're going to name this criteria 3:1 To Surface. Where are we going? The existing grade surface. And then how are we going to get there? Now this is answered here but there's a few questions here first. For example, a feature line that we may be daylighting from, especially if we're daylighting an entire site.
A five acre site along the perimeter as we begin to daylight that perimeter, begins to get very long very quickly. On a five acre lot, it could easily turn into almost a mile in length, depending of course on the edges that we're working with. And so because of that, and there's so much information that's trying to tie in at every one of these points along this feature line, it's trying to figure out the fastest method to use. So it's asking how do you want to search? Do you want to check to see if I'm in cut first? Or if I'm in fill first? What I've found is by the time I figure out where this feature line may be the most in, whether the daylight is going to be more in cut or more in fill, the software could have worked through the process already.
So I'm just going to leave it at cut and don't want to be prompted about it. We did name this 3:1 To Surface, so we'll change all of those and we have already talked about that interior corner overlap. So in this case, when we choose 3:1 To Surface, if we've identified which surface we're daylighting to, we won't receive any prompts at all when we use this criteria. So we understand the criteria. There's three key factors for automated grading in Civil 3D. We need a base reference point.
That's an existing feature line we're going to be grading from. And then we need to provide a criteria selecting the correct criteria from our set to answer the two questions. Where are we going? And how are we going to get there?
This course gets you up and running with AutoCAD Civil 3D. First, instructor Josh Modglin shows how to model a surface, lay out parcels, and design geometry, including the making of horizontal alignments and vertical profiles. Next, Josh demonstrates how to create corridors, cross sections, pipe networks, and pressure networks. Then, he covers working with feature lines and grading objects, and how to share your data. He wraps up by providing an overview of plan production tools.
- Navigating the Civil 3D interface
- Using point groups and description keys
- Importing survey data
- Managing figures
- Creating and analyzing surfaces
- Creating parcels
- Working with alignments
- Working with profiles and profile views
- Working with assemblies and subassemblies
- Creating Basic and Advanced Corridors
- Using an Intersection Object
- Making sample lines, cross sections, and section views
- Creating a pipe network
- Understanding pressure parts
- Creating and editing feature lines
- Creating and editing grading objects
- Sharing and referencing data
Skill Level Beginner
Some of the exercise files do not properly function.
This course was built to work with the latest release of AutoCAD Civil 3D. If you are not running AutoCAD Civil 3D 2018 there are some exercise files that will not work for you.