1. ## Steep Slopes - Grading Analysis

So I am faced with the problem of locating all slopes that are greater than 15% on a 50 ac. site.

I've built my surface, and everything appears to be set.

Is there a way for me to have LDD go through my surface, and create either polylines and/or 3DFaces for any area that is greater or equal to a 15% grade?

I've read through nearly every help article, and am really stuck.

Any help would be greatly appreciated!!

Regards,

Luke

2. ## Re: Steep Slopes - Grading Analysis

Originally Posted by luke.repsher
So I am faced with the problem of locating all slopes that are greater than 15% on a 50 ac. site.

I've built my surface, and everything appears to be set.

Is there a way for me to have LDD go through my surface, and create either polylines and/or 3DFaces for any area that is greater or equal to a 15% grade?

I've read through nearly every help article, and am really stuck.

Any help would be greatly appreciated!!

Regards,

Luke
Make the surface you want analyzed the current surface.
Then go to
Terrain>Surface Display>3D faces (see first screenshot)

You will get a dialog box called "Surface Slope Shading Settings" (second screen shot)

Change the number of ranges to be how many different slope situations you want to analyze.

Click on Auto-range and another dialog box appears giving you the max and min slopes. It will then average the slopes and assign the ranges based on the max and min. Then it shows you the slopes to adjust. Set one range to end at 15 and the next range to start at 15. Select the colors you want for each slope range. I like to select "by-layer" and change the layer color after the evaluation is done. (third screenshot)

Click OK and OK.

It will ask you if you want to erase existing slope evaluation stuff, I usually choose yes to avoid cluttering the drawing.

It will then give the Range Statistics. Click on Legend to insert this information in the drawing. This will bring up the legend dialog box. (fourth screenshot) Select the information you want to include in the legend. (hint-only select the "none" option at the end, it won't include any information after the "none")

Then 3D faces are created on the different layers depicting the different slope ranges and the legend is inserted with the data you selected to display.

**Warning** This greatly increases the size of your drawing.

Hope that helps. Let me know if any of it doesn't make sense.

3. ## Re: Steep Slopes - Grading Analysis

Originally Posted by ammon
Make the surface you want analyzed the current surface.
Then go to
Terrain>Surface Display>3D faces (see first screenshot)

You will get a dialog box called "Surface Slope Shading Settings" (second screen shot)

Change the number of ranges to be how many different slope situations you want to analyze.

Click on Auto-range and another dialog box appears giving you the max and min slopes. It will then average the slopes and assign the ranges based on the max and min. Then it shows you the slopes to adjust. Set one range to end at 15 and the next range to start at 15. Select the colors you want for each slope range. I like to select "by-layer" and change the layer color after the evaluation is done. (third screenshot)

Click OK and OK.

It will ask you if you want to erase existing slope evaluation stuff, I usually choose yes to avoid cluttering the drawing.

It will then give the Range Statistics. Click on Legend to insert this information in the drawing. This will bring up the legend dialog box. (fourth screenshot) Select the information you want to include in the legend. (hint-only select the "none" option at the end, it won't include any information after the "none")

Then 3D faces are created on the different layers depicting the different slope ranges and the legend is inserted with the data you selected to display.

**Warning** This greatly increases the size of your drawing.

Hope that helps. Let me know if any of it doesn't make sense.
Ok, i think I understand this.

The first question I have is what should I have my base elevation set to? 424' is the lowest point on my drawing.

Secondly, I want to hatch everything that has a 15% grade or higher. So I would assume my range for the 3D Face would be 15 to 100? Right?

If that is correct, why does AutoCAD create arbitrary numbers in this field like in your third screen shot? 11056.00 11056.00%?

Are these numbers elevations? Or are they grade percentages? Let me know when you get the free chance!

Thanks!!!

Luke

4. ## Re: Steep Slopes - Grading Analysis

Originally Posted by luke.repsher
Ok, i think I understand this.

The first question I have is what should I have my base elevation set to? 424' is the lowest point on my drawing.

Secondly, I want to hatch everything that has a 15% grade or higher. So I would assume my range for the 3D Face would be 15 to 100? Right?

If that is correct, why does AutoCAD create arbitrary numbers in this field like in your third screen shot? 11056.00 11056.00%?

Are these numbers elevations? Or are they grade percentages? Let me know when you get the free chance!

Thanks!!!

Luke
I'm not sure on the relevance of the base elevation. I've always just left mine at where ever AutoCAD put it, I think it's always been 0.

The numbers are grade percentages. If you let AutoCAD do the auto-range thing, it selects the minimum and maximum slopes. The 11056.00% is basically just vertical areas in the project I was working on at the time, and was the maximum slope that it found on the surface. I use that as the maximum. If I were to do an analysis of 15% or higher slopes I would make 1 range 15 to whatever LDD gives me as my maximum. that way it only creates 3D solids where the slope on the surface is 15% or greater.

As far as hatching that area, you might have to settle for a solid color, or trace around the boundaries, which could get tedious, depending on the project.

5. ## Re: Steep Slopes - Grading Analysis

Originally Posted by ammon
I'm not sure on the relevance of the base elevation. I've always just left mine at where ever AutoCAD put it, I think it's always been 0.

The numbers are grade percentages. If you let AutoCAD do the auto-range thing, it selects the minimum and maximum slopes. The 11056.00% is basically just vertical areas in the project I was working on at the time, and was the maximum slope that it found on the surface. I use that as the maximum. If I were to do an analysis of 15% or higher slopes I would make 1 range 15 to whatever LDD gives me as my maximum. that way it only creates 3D solids where the slope on the surface is 15% or greater.

As far as hatching that area, you might have to settle for a solid color, or trace around the boundaries, which could get tedious, depending on the project.
Thanks so much for your help!! Solid colors will work just fine!!!

6. ## Re: Steep Slopes - Grading Analysis

Originally Posted by luke.repsher
Thanks so much for your help!! Solid colors will work just fine!!!