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