leveling (a most elevating passtime). the problem: i’m here standing on ground that’s 123.467...
TRANSCRIPT
LEVELING
(a most elevating passtime)
The problem:
I’m here standing on ground that’s 123.467 metres above mean sea level
I need to know the elevation of the ground here
(so I can choose the right club)
The solution?
Then measure the vertical distance down to the green.
Simply extend a
level linefrom my feet
to the green
There’s only one catch…
I don’t have a carpenter’s level
that long!
Any suggestions?
Call this point A
and this point B
Sally sets up a level hereManny holds the
rod on Point ASally’s level projects a level line of sightThe rod reading is the vertical distance
between the level’s line of sight and Point A
This is called a Back Sight (a rod reading taken on a point of known elevation)
Why Back Sight ?
This is the direction of the survey, right?
But the reading was taken while looking Backwards
The Height of Instrument (HI) is
?1.981 m
If the elevation of Point A is 123.467 m then what’s the elevation of the instrument’s line of sight?
The Back Sight (BS) was 1.981 m
123.467 m
125.448 m
123.467 + 1.981 = 125.448 m
What now?
Whenever the sight is too low, too long or blocked by obstacles (trees, buildings,
etc)
this is a temporary point (a rock, a pipe,… a hard
place)
In surveying we call it a Turning Point
If Sally aims the level scope at Point B
Manny’s rod, fully extended is too short to reach the line of sight
she could find the elevation of Point B by subtracting it from the HI
then takes a rod reading
Only one problem…
an intermediate point is required to transfer the
elevation.
TP 1Sally aims the scope at TP 1
and takes a rod reading of 2.216 m
This reading is called a Fore Sight because it was taken in the same direction
as the survey (forwards)
To find the elevation of TP 1, subtract the fore sight from the HI:
Sally’s got to get down!
Elevation of TP 1 = 125.448 – 2.216 = 123.232
2.216125.448
123.232
What Next?
(she may as well get closer to Point B too)
Sally takes another rod reading on TP 1
What type?
That’s right, a back sight
The BS on TP 1 is 0.358 m
0.358
123.232 + 0.358 = 123.590 mAnd the new HI is…
123.590
-1.602121.865
123.467
Finally…
So what was the change in elevation from A to B?
Sally aims at Point B and takes another rod readingAnd the elevation of Point B
is…
(Negative means losing elevation)
The FS on Point B is 1.725 m
1.725
123.590 - 1.725 = 121.865 m121.865 – 123.467 = -1.602 m
123.590
The change in elevation in a leveling survey is always calculated as:
Elev = Elevfinal – Elevstart
Furthermore, every leveling survey starts with a back sight on a known elevation and ends with a fore sight
on an unknown elevation
Let’s look at this survey in profile view:
1.981 2.216
0.3581.725123.467
125.448
123.232
123.590
121.865
Point A
Point B
TP 1
Given the elevation of Point AFind the elevation of Point B ?
First Setup
BS
HI = 123.467 + 1.981
FS
Elev TP 1 = 125.448 – 2.216
Second Setup
BS
HI = 123.232 + 0.358
FS
Elev Pt B = 123.590 – 1.725
As leveling surveys go that was pretty
basic
Usually several turning points are
needed and the survey must end
with a fore sight on a known elevation
to check the accuracy
Survey notes are required to document
measurements and calculations
Lets look at how this information is
documented in field notes
First of all, the field books have pages that are lined in the following format:
………………………………………………………………………………….
……………………………………………………………
Project:
Date: Page: 2
Even numbered pages are for
recording measurements and doing calculations:
………………………………………………………………………………….
……………………………………………………………Page:
Project:
Date: 3
Odd numbered pages are for descriptive information
(labels, diagrams) to explain
measured data and also for project
titles
………………………………………………………………………………….
……………………………………………………………
Project:
Date: Page: 2
For the survey shown in this
presentation the notes should be
logged like this…
1. Identify the project and date2. Fill out column headings as shown3. Then record numbers as they’re measured or calculated
What club should I use?
05-09-08
BS HI FS ELEVSTA
Until you become experts (who don’t make mistakes) triple space! 123.467Point A 1.981 125.448
2.216TP 1 123.2320.358 123.590
Point B 1.725 121.865
There’s a way to check the math…its called the Math Check and it goes like this:
1. Find the sum of the back sights (BS)
2. Find the sum of the fore sights (FS)
3. Find the change in elevation (Elev)4. If BS – FS = Elev, then the elevations and HI’s calculated are correct
BS =
Math Check
2.339 FS = 3.941 Elev = -1.602
Since BS – FS = Elev
Math is Correct
Reduced by:
S.S.
√ by: M.R.
5. Then you must confess: the notes were reduced by Sally Surveyor and the math check was performed by Manny Rodman BS – FS = 2.339 - 3.941 = -1.602
………………………………………………………………………………….
……………………………………………………………Page:
Project:
Date: 3
The description page should
indicate who did what…
S.S.:
M.R.:
[123.467] Point A: 175 yd mark, centre fairway, 12th hole, South Course, Angus Glen G. & C. C., Markham, Ont.
Then a description of our starting
point…True elevation (known from previous surveys)
Note that description begins on same line that this point is referenced in the notes Point B: 15 yd before cup, green, 12th
hole, South Course, Angus Glen G. & C. C., Markham, Ont.
Note that there is no description for the turning point
Note that the description for Point B does not include an elevation because we don’t know its TRUE elevation
And finally a description of our
ending point…
instrument
rod in hand