End area calculation

[sodengineer]

Here is a blast from the past.

Waaay back when I was a field engineer, we had an algorithim that would allow us to compute the cross-section area for cut or fill sections, based on x,y coordinate pairs. As I recall, we took the last two coordinate pairs and added them to the end of a string of coordinates, then did some kind of cross multiplication to get the area.

We would then average the areas, multiply by the distance between sections, etc.

Does anyone know what I'm talking about? Can you describe the process? I have a few cross sections I need to compute, and I don't want to go to all the trouble of learning a new software package for something simple like this.

As always. Thanks, this forum rocks.

 

[CarlB]

Check any Survey textbook. Yes is pretty simple, plug into a spreadsheet.

On-line, here are 2:

http://www.tpub.com/inteng/10e.htm

http://www.eng-tips.com/viewthread.cfm?qid=227830&page=3

 

[Ron]

Agree...it's called the average end area method. Google it and you'll find a few examples.

 

[sodengineer]

Thank you both. That is exactly what I want to do.

BTW, I checked it with my HP 41CX with the survey pack. Answer is within 3%.

 

[BigH]

My god - what would we do if we didn't have computer software? - oh, yeah, we might do hand calculations (sorry - but I did so many of them by hand when I was first starting out . . . - used a planimeter and a table and went to it!)

 

[dicksewerrat]

Didn't you have a slide rule?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[BigH]

Actually Dick, I did - also had sides of the paper for hand mulitiplications and fingers - no abacus. The slide rule was a beaut that my dad bought me to go to college with . . . As SRE would point out - they give you perspective on accuracy!

 

[ishvaaag]

The finest thing about this I have ever found is to model the surface at autodesk inventor (what can readily be done on sweep, loft etc commands), and if necessary (more common in our architectural works) extrude down the foundation volume for intersection: then inventor in the physical properties gives you the volume of ground to excavate with good accuracy. Of course InRoads, Autodesk Civil etc will have their way.

Yet I like very much old methods of calculation and design; I presently have rediscovered the way o get the square root graphically by I think Archimedes; so, the Simpson's (other Simpsons) rule look some times in the day quite modern.

 

[sodengineer]

Slide rule?
Hmm, last week I cleaned out my father's basement, and we got rid of an old Monroe hand crank adding machine. He said he used it for figuring cuts and fills. This was before the advent of digital computers.

I needed to relearn this process to insure that I wasn't just trusting the software. I needed to know that the answer the computer gave me was correct. As BigH says, it gives you a new perspective on accuracy.

I worked on a large canal project several years ago. My standard comment was that we are doing the same things the romans did, but we have computers and diesel powered equipment.

Thanks all.

 

[BigH]

I remember that Monroe from my dad . . . At the time you could get a Monroe calculator for basic math only and sq.rt - all for $250!!

 

[ishvaaag]

Well now you can have two graphical sqrt calculations for free

 

[ishvaaag]

Other

 

[ishvaaag]

and the mother of the previous