Notifications
Clear all

Obtuse Scalene Triangle calculation

20 Posts
4 Users
0 Reactions
5 Views
 rfc
(@rfc)
Posts: 1901
Registered
Topic starter
 

Hi all. Still dubbing away at my self guided education. Harder than ever with a full time job. I am attempting to confirm my calculations of the width of a Right of Way corridor, as measured along a property line. See attached. I've done the math using the formulae for an obtuse scalene triangle. 10th grade geometry, yes, but still a brain challenge.

The calculations I get are:
From the property corner to the nearside of the ROW: 69.943ƒ??
From the property corner to the farside of the ROW: 127.720ƒ??,
?ÿ
Making the ƒ??widthƒ? of the ROW as measured along the property line, 57.78ƒ??

CAD seems to confirm the same thing. Can anyone confirm my math? Thanks in advance!

?ÿ

 
Posted : 14/06/2021 5:11 am
(@bill93)
Posts: 9834
 

Welcome back after 2.5 years.

I'm on my phone-may check calcs when at desk.

 
Posted : 14/06/2021 5:19 am
(@bill93)
Posts: 9834
 

I agree, getting 57.778 ft, but am a bit nervous about expressing it so precisely given even foot inputs.

 
Posted : 14/06/2021 6:19 am
 rfc
(@rfc)
Posts: 1901
Registered
Topic starter
 

So, given the precision of the numbers on the survey, i.e. "80.0'", "Radius=150.0'" etc., the proper precision of the calcs. would be 69.9' and 127.7', rendering the distance between them 57.8'?

 
Posted : 14/06/2021 6:27 am
(@bill93)
Posts: 9834
 

I just looked at the sketch at first.?ÿ Seeing now that those are design values and not measurements, then the design value for your distance can be to any precision, but what is put on the ground by measurement will have its own degraded precision.

 
Posted : 14/06/2021 6:53 am
 rfc
(@rfc)
Posts: 1901
Registered
Topic starter
 

Thanks Bill!

I'd love it if someone could confirm the three dimensions in CAD (vs. geometric calcs); i.e Distance from the corner to the near side of the ROW: 69.943; Distance to the far side of the ROW: 127.720, making the "width" of the ROW as measured along the property line 57.78'.

I surveyed the driveway long ago and always assumed it was in the center of the ROW and never bothered surveying the ROW. That appears to be not the case. My suspicion is that the ROW was "created" in CAD completely...never staked on site. Then when mr. bulldozer guy put the driveway in, he paid attention to the topography, not the survey...In some places the driveway departs completely from the bounds of the ROW.

 
Posted : 15/06/2021 4:32 am
(@bill93)
Posts: 9834
 

I added some more bearings and distances to my file, and get 69.941, 127.718, and?ÿ 57.777 all close enough to your numbers.

But I can't close the loop of the driveway center lines and the road right of way line.?ÿ They miss by almost 25 ft at the cul-de-sac.?ÿ Either I copied or interpreted something wrong or it's sloppy.?ÿ What is the bearing on the 302.8 ft line?

 
Posted : 15/06/2021 8:36 am
 rfc
(@rfc)
Posts: 1901
Registered
Topic starter
 

@bill93 :

It's N25-55-05E. Our property line ends on the 1,680.2' line, so I've been concentrating for now on A to B. I have a later survey that another surveyor did recently that updates the right of way. It's quite amazing what he did to get the "new" right of way to match the deeded right of way.

 
Posted : 15/06/2021 8:58 am
(@mathteacher)
Posts: 2081
Registered
 

Can't do CAD, but here's what Geogebra (a free on-line math teaching software) gives.

image

Note that 4 concentric circles and a triangle describe the figure graphically. As long as the 112.78 degree angle is held constant, the triangle can be rotated about the center to any orientation without changing the numbers.

Construction wise, the center of the circles is at (200,200). Point A is arbitrarily placed on the 80-foot radius circle and then point O prime is determined by the 112+ degree angle. Intersection points are marked and the software provides the measurements.

So the only inputs are the fundamental measurements. The black box does the rest.

Hope this helps.

 
Posted : 15/06/2021 11:26 am
(@mathteacher)
Posts: 2081
Registered
 

@rfc :?ÿ The red and purple numbers and segments in the drawing below are what I think you're asking about. Pretty close to Bill's numbers and to yours. Who knows what goes on in different black boxes.

image

?ÿ

?ÿ

 
Posted : 15/06/2021 2:01 pm
 rfc
(@rfc)
Posts: 1901
Registered
Topic starter
 

@mathteacher Thank you, Sir! That's the "cleanest" depiction of the problem I've seen. I'll check out Geogebra on line. Now that the numbers are confirmed I'll move on to staking it in the field, and mapping the existing driveway. Thank you also, @bill93.

 
Posted : 16/06/2021 1:56 am
(@brad-ott)
Posts: 6185
Registered
 

@mathteacher those Geogebra sketches are beautiful!

 
Posted : 16/06/2021 3:42 am
(@mathteacher)
Posts: 2081
Registered
 

@brad-ott?ÿ

It's great software. Sort of CAD light double light with a ton of higher math functions. The burning pedagogic question for me was whether to incorporate learning Geogebra into the class or just use it to create precise drawings that made sense to students.

I opted for the second option simply because the amount of material we had to cover used up all the class time. We needed a separate little 30 minute slot ever day for teaching usable tech, but that never happened. Pep rallies and such did, though.

 
Posted : 16/06/2021 4:40 am
(@brad-ott)
Posts: 6185
Registered
 

@mathteacher I shared a link with my HS senior.?ÿ He probably thinks I am ultra cool now.

 
Posted : 16/06/2021 6:19 am
(@bill93)
Posts: 9834
 
Posted by: @brad-ott

Did a HS senior ever think Dad was cool?

And if he did, he probably wouldn't say cool now.?ÿ It's so 1970's.?ÿ There has to be a new word.

 
Posted : 16/06/2021 6:26 am
Page 1 / 2