Grading Tools (grade to surface; not working as expected)

[Anonymous]

Hi, this is my first post on these forums. I'm hoping that somebody has come across this situation I'm in and will be able to help me out a little. I've done some extensive searching, but haven't been able to solve my issue.

I have the bottom of a buttress keyway drawn with a feature line. The feature line has the correct elevations. I'm trying to grade from the bottom of the key to the current surface conditions (current surface created from photogrammetry with a quadcopter and GCPs). I first tried grading from the feature line representing the bottom of the key, but Civil 3D didn't really like that at all. Some areas didn't have any grading projection lines. Next I tried using the featureline offset command to create a second feature line with radiused corners. I only offset by a couple of feet at a 2:1 slope. I filleted some of the sharp corners and eventually arrived at the featurline offset that I have labeled in the attached image.

I'm wondering why the area in the top right of the attached plan view screenshot isn't correct. I'm not sure if there are problems with the grading projection lines. Do I need to add more PI points on the featureline?

I've also included a screenshot looking at an oblique angle so you can more easily see some of the issues with the surface. I would like to correct these issues so I can have a smooth surface without any near vertical cuts.

Let me know if I can provide any more details.

[Neilw_05]

It is hard to tell what is happening from the images alone. Could you post your file or a subset of the data that can be used to asses the problem?

[Neilw_05]

I can say that it appears the gradings are crossing each other due to the long distances required to catch the existing terrain. Still it will help if you can provide a file to devise a workaround.

[Anonymous]

Attached is a .zip including the file and all dependencies. Let me know if I can provide anything else.

[Neilw_05 · Accepted solution]

2 things that will need to resolve:

1. There is a steep slope (269%) that you are trying to project to daylight. This should be mitigated by a flatter target footprint that reduces the abrupt change in slope in this area. (See attached markup). Apparently you have already attempted to do this.

2. Due to the long distances to the daylight target you will need to provide an intermediate transition featureline to mitigate the overlapping slopes in the grading objects. Ideally you will want to make the projections radiate AWAY from each other rather than cross. This can be done by creating an intermediate featureline as shown in my markup sketch which I am attaching. Of course these solutions require a compromise in the grading parameters but sometimes that is necessary to make it work in the real world. The slopes may need to vary in this area..

[Anonymous]

Great, thank you so much Neil! Your two points sound like some good suggestions and make a lot of sense.

Regarding your first point, I did offset the keyway featureline and deleted some PIs and added some new PIs at a 3:1 slope with the "Set Elevation by Reference" tool to try and make that area a little flatter. Does this technique sound reasonable to try and get that area to play a little nicer with grade to surface?

[Neilw_05]

Yes. You are on the right track. You want to reduce the extremes as much as you can tolerate. You next need to mitigate the grading overlaps per my previous post.

[Anonymous]

I think I'm more or less on the right track now. There are some areas that are a bit off, but I'm guessing I can continue to play around with the intermediate feature line or perhaps add a second intermediate feature line(?) to try and improve these areas.

I created the intermediate feature line you see in the attached screenshot by creating it in the same site and grading group as the projection grading. I deleted the projection grading and used infill to grade up to the feature line. I then used grade to surface to continue the rest of the way to the existing grade surface. Does this sound like a reasonable way to do this or is there a better way?

[Neilw_05]

You are doing it just right. You have a good grasp of the tools. Yes you might need to add more featurelines to fix the overlaps. 

[Neilw_05 · Accepted solution]

You would likely want to use the elevation by adjacent tool to make those new featurelines have elevations at your desired slope from the uphill featurelines. For example if you want the slope of the grading to be 2:1, use the Elevation by Adjacent tool to set elevations along the downhill featurelines that are 2:1 slope from the nearest uphill featurelines. The tool will add elevation points to the target featureline where it can. Sometimes it doesn't give good results if you let it add the elevation points for you. What I often do is add elevation points to the featurelines BEFORE I run the tool. Then it has more data to work with and gives better results. You can add elevation points at some interval that you feel is good enough. You don't want too many as it will slow down the processing. You would add them to both the source featureline and the target featureline to get the best results.

[Anonymous]

I didn't know about that tool, so thank you for introducing it to me. I just took a quick look at the help article for that tool and it looks fairly straightforward like you mentioned. It looks like it will really help with getting the elevations on that second or third feature line correct. I'll take your suggestion as well to add elevation points to the feature line prior to using the "Adjacent Elevations By Reference" tool.

Thanks very much for lending your hand with this, Neil. You've helped me out a great deal.

[Anonymous]

Do you have any recommendations for tying in grading around the ends of the keyway? I tried using "Create Transition", but that screwed up the projection lines and contours for the rest of the grading. I thought maybe I could break the keyway offset feature line where the uphill feature line meets up with it, but I can't break a feature line that has grading tied to it. I've tried to illustrate some of what I'm talking about in the attached screenshot.

EDIT (added screenshot): I've gotten the surface all the way down to the keyway by using grade to surface and then the transition tool. Now I'm not sure how to tie in the grading projection from the uphill feature line to the feature line that represents the bottom of the key.

[Neilw_05]

I'm afraid I don't understand what you are trying to do. If it would solve your problem by breaking the featureline, go ahead and delete the grading and recreate it afterwards. It shouldn't be a lot of re-work.

[Anonymous]

I ended up doing just that and like you said recreating the grading wasn’t very time consuming.

I was trying to articulate that I wanted to create a transition between grading projections emanating from two different feature lines. I don’t think that’s how the transition tool works though. 

At any rate you helped me solve my problem by adding those additional feature lines. Thank you

[Neilw_05]

I'm glad you got it sorted out.

As for the transition, let's say you have 2 featurelines that are graded to different targets. Because they are not connected and have different targets, you will have a gap between the ends of the gradings. For that scenario you can draw a featureline between the outer target featurelines to close the gap and use an inflill. Then you can apply a grading to the piece that you used to close the gap. Hope that makes sense. It may not be what you were trying to do but I took a shot at it.

[Neilw_05]

By the way, in regard to the transition tool:

It can only be used on a single featureline. It cannot be used to close the gap between 2 graded featurelines. For example if you are grading a featureline to a target surface and you want to transition from 3:1 slope to 2:1 slope, you create a gap in the grading regions and apply the transition to the gap. It will then transition from the 2:1 grading to the 3:1 grading.

You cannot use transitions if one of the gradings is a surface and the other is not. Nor can you use a transition if the gradings are targeting different surfaces.