Civil Drafting with AutoCAD Project-Civil Drafting with AutoCAD Project

[nelsonm]

Hi, I'm a student from Pen Foster College and I have a trouble with this Project. I would like to get some help.

For this part: Drafting the Existing Site Plan (Sheet 1):

"Now, you need to figure out where the contour intervals cross the grid lines between each spot elevation. Create contours at 10′ intervals for just the 100′–180′ contour lines. You can estimate where a contour line intersects a grid line using interpolation. You can interpolate the position of the contours by estimating between the known locations of the spot elevations. You may find it quicker to set up a spreadsheet to help you calculate all the locations." Can someone guide me to get started with this part? please

3. Civil Engineering Drafting.pdf

[ReMark]

In other words, you are having trouble understanding the concept of interpolation, correct?  The mathematical interpolation of contours goes like this.

 

Let's say we have two spot elevations A & B. A = 32.7 and B = 54.0. The distance between A & B = 50 feet.

 

We want to know where our 40-foot contour would fall between spot elevations A & B.

 

First obtain the total elevation difference. This is done by subtracting A from B. 54.0 minus 32.7 = 21.3.

 

Next, we want the difference in elevation between our 40-contour interval and the nearest spot elevation which in this case is A or 32.7. That works out to be 7.3.

 

Now we need to calculate the distance (let's call this "d") we need to go from spot elevation A to our 40-foot contour. That takes the form of:

 

d/7.3=50/21.3 or d=7.3*50/21.3 = 7.3*2.347 = 17.13 or the distance, in decimal feet, to our 40-foot contour.

 

Got all that?  Good.  Now go start interpolating. 

[nelsonm]

56 minutes ago, ReMark said:

In other words, you are having trouble understanding the concept of interpolation, correct?  The mathematical interpolation of contours goes like this.

 

Let's say we have two spot elevations A & B. A = 32.7 and B = 54.0. The distance between A & B = 50 feet.

 

We want to know where our 40-foot contour would fall between spot elevations A & B.

 

First obtain the total elevation difference. This is done by subtracting A from B. 54.0 minus 32.7 = 21.3.

 

Next, we want the difference in elevation between our 40-contour interval and the nearest spot elevation which in this case is A or 32.7. That works out to be 7.3.

 

Now we need to calculate the distance (let's call this "d") we need to go from spot elevation A to our 40-foot contour. That takes the form of:

 

d/7.3=50/21.3 or d=7.3*50/21.3 = 7.3*2.347 = 17.13 or the distance, in decimal feet, to our 40-foot contour.

 

Got all that?  Good.  Now go start interpolating. 

Thank you so much for you help! I made a spreadsheet in excel, can you take a look? and I have another question: how can I know in which squares to place the interpolations?

[BIGAL]

Welcome aboard, a little surprised that the exercise is to interpolate contour points. Given the availability of TIN software. That is a lot of points to tackle. Glad I am not doing that task. If I had to do it yes would use the method shown by @ReMark. But I would use a lisp to do the calculation making a Point at the correct distance then join all the points with a pline. I hope the little crosses are 3D so can pick pairs.

 

Certainly have used the interpolation method in many other civil tasks, so well worth while learning how to do it.

[ReMark]

11 hours ago, BIGAL said:

Welcome aboard, a little surprised that the exercise is to interpolate contour points. Given the availability of TIN software. That is a lot of points to tackle. Glad I am not doing that task. If I had to do it yes would use the method shown by @ReMark. But I would use a lisp to do the calculation making a Point at the correct distance then join all the points with a pline. I hope the little crosses are 3D so can pick pairs.

 

Certainly have used the interpolation method in many other civil tasks, so well worth while learning how to do it.

BIGAL: I agree with you 100%.  Unfortunately, Penn-Foster does not offer TIN software nor do they teach its use.  And, unless a student has some basic knowledge of LISP to begin with, I doubt they would even think of taking advantage of its functionality.  In this project the old way is the best the students can count on.  Re: Points.  The project is not being done in 3D; strictly 2D all the way.