I don't know what they're asking for

[JonnaMcSki]

Hello,

 

I'm working on a project for Penn Foster the Structural Civil Drafting Project. I've created the grid with the surveyor's spot elevation and grid. I have the spread sheet ready to go. I'm at a point where I need to interpolate contour lines. I don't know what they are asking at all. I understand what interpolation is and the mathematical equation that is needed. We have not done this before. This is what it says. 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.

 

1.) How do I know where the intervals cross the lines? Are they asking us to interpolate what the level is in the exact middle of the spot elevations? If not, what outcome am I looking for? 

 

2.) When it calls out, "for just the areas that are in-between the height of 100' -180'? I'm having a hard time with tis because the images students have shared have contour lines in places that have spot elevations lower than 100.

[tombu]

If one point has an elevation of 90.45 and the next has an elevation of 103.25 there would be a DE (difference in elevation) of 12.8 but to prorate the distance from the first point you need the distance between those points. You need to interpolate all the points that fall on those 10' contours horizontally, vertically & diagonally in order to sketch those contour lines correctly.

[JonnaMcSki]

Hello Tombu,

 

are you saying that the outcome is to get the points for every 10'?

 

What does 100'- 180' have to do with anything?

 

 

[BIGAL]

This is just so old fashioned question no one does contours manually any more that's like when I started Civil Engineering back in the 80's. 

 

Ok the answere is to do with ratios

 

103.25-90.45 = 12.8

103.25-100 = 3.25

 

so

3.25/12.8 * distance between the 2 points is the location of contour 100, its a repetive sequence very time consuming.

 

100-180 means look for point ranges 100-110 110-120 120-130  ..........

 

Again why would a training exercise have something that is just so out of date.

 

Thousands of points contoured in seconds. TIN software is out there free I would look at that. 

[JonnaMcSki]

Hello,

 

Yes, in my research I have found this is unnecessary but we need to do it to pass the class. 

I see you used 100 for your why? Are contour lines always in the 10s like 100,110,120? how do I figure out for every 10' when I'm given 50' increments and when you find contour line for the 100' spot is that right in the middle of the two points so you can break it up in to 10' increments that way? 

[BIGAL]

No, you need to draw say a line between the points eg 103.25 90.45 so if 50' then 3.25/12.8 * 50 = 12.695 so draw a circle on the 103.25 of rad 12.695 where it crosses the line is contour point 100. Go to next grid and keep going its going to take a while, its a case of join the dots. 

[JonnaMcSki]

Okay Maybe I'm just fried but I'm more lost than ever. I have no recollection of going over rad and how to use it in this situation. 

 

 

Edited February 22, 2022 by JonnaMcSki
relied it didn't make sense

[tombu]

3 hours ago, BIGAL said:

This is just so old fashioned question no one does contours manually any more that's like when I started Civil Engineering back in the 80's. 

In school back in 1980 we did a traverse and topo of our campus with a transit for angles and reading stadia from a Philly-rod for distances. All of us took turns doing everything. When we finished each of us had to calculate all those points and create a topo map on our own drawing the contours just like this. It was the only survey class we had that included doing field work.

[BIGAL]

tombu we did the same surveyed a park and designed a drain into the lake all by hand including plans.

 

For Jonna

 

[steven-g]

All it is asking you to do is create the contours 100, 110, 120, 130, 140, 150, 160, 170 and 180.

Every 10' for just the contours between 100'-180'

Anything above or below that is not required for this exercise

[SLW210]

I have moved your thread to the Student Project Questions Forum.

[ReMark]

Hoping this helps straighten you out re: interpolation.  (Project 6 - 562 Ocean Avenue)

 

The mathematical interpolation of contours goes something 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 ft. 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.

 

Make any sense to you?

Edited February 22, 2022 by ReMark

[ReMark]

12 hours ago, BIGAL said:

This is just so old-fashioned question no one does contours manually any more that's like when I started Civil Engineering back in the 80's. 

 

Ok the answer is to do with ratios

 

103.25-90.45 = 12.8

103.25-100 = 3.25

 

so

3.25/12.8 * distance between the 2 points is the location of contour 100, it's a repetitive sequence very time consuming.

 

100-180 means look for point ranges 100-110 110-120 120-130  ..........

 

Again, why would a training exercise have something that is just so out of date.

 

Thousands of points contoured in seconds. TIN software is out there free I would look at that. 

Why would a training exercise have something that is just so out of date?  Because it is a Penn-Foster AutoCAD project and the course teaches how to use AutoCAD not how to use TIN software.

[JonnaMcSki]

okay let start from the beginning. I now believe that I have no clue what interpolating is and no clue what my goal is here. 

 

What I do think I get: 1.) the mathematical equation is to fine the consistent depths like the land measurers 20 feet along l path X. 

                                        2.) the equation helps you find the difference in distance between the two numbers so you can find where the contour line is placed 

 

What I don't get: 1.) How do you incorporate 10' into the equation? 

                            2.) how many contour lines will fall between the two lines on the grid?

let's start with that please and thank you

                          

I posted this before seeing the new explanations I will read those so we can now ignore this I'll repost If I still don't get it after reading the new posts.

 

 

Edited February 22, 2022 by JonnaMcSki

[CyberAngel]

9 minutes ago, JonnaMcSki said:

okay let start from the beginning. I now believe that I have no clue what interpolating is and no clue what my goal is here.

If it helps, think of interpolation as a simple algebra problem. You know the X and Y values of two points. You can draw a line between those two points. Given another value of Y (the contour), where does it fall on that line? That's where your contour crosses the grid. I believe that's what ReMark was trying to explain in his first comment.

 

To draw a contour, you have to find all the points where it crosses the grid and connect the dots. If you know how to draw a spline, that will help smooth out the kinks.

[JonnaMcSki]

okay I think I get It I'm going to try to do some equations first once I work one or two out then I'll mark this as solved once I'm certain. 

 

I don't believe this is the same project you worked on BigAl it's a women's property who wants to build a house, there is no mention of a park yet.

[JonnaMcSki]

 I have my first point here on my spreadsheet. I have found where the 100 spot of the contour line is between the 92.2spot and the 113.3 spot do I also need the fine the 110 spot of the contour line also between the 92.2 spot and 113.3 spot?

[ReMark]

If your first spot elevation is 92.2 and the second spot elevation is 113.3 then you will have a 100.0 foot and a 110.0 foot contour interval between the two points.  

[JonnaMcSki]

So, now I get mushy. Thank you so much for all of your responses. I was feeling hopeless when I closed up yesterday. When I received my update on this page and saw how many of you who had my back wanting to help. I was no longer hopeless and was instead filled with hope Thank you so much  

[ReMark]

Unfortunately, the person that should have your back is your P-F instructor.  Instructors should be available to answer student questions regarding the assigned projects.  They should have also provided a clear explanation of how to interpolate contour points between spot elevations in the project instructions.  P-F is not known for providing helpful and timely assistance.  They are, however, very good at separating a student from his/her money though.  I hold them in the lowest regard.  Seems they have not changed their ways even after all this time.  Too bad.