Horizontal Distance

Horizontal Distance Measurement Tape Odometer Subtense Bar Stadia EDM

Distance Measurement  Devices and accuracy: •

 Older technologies “ quick look” • • • • • •

Pacing  !"# Optical range$inders ! "# Odometers !%## Tacheometr& ' stadia ! "## Subtense bar ! (### Tapes ! !#)###

• Modern Technology echnology::  - Electronic Distance Measuring (EDM) devices: 2 +2 

Distance Measurement  Devices and accuracy: •

 Older technologies “ quick look” • • • • • •

Pacing  !"# Optical range$inders ! "# Odometers !%## Tacheometr& ' stadia ! "## Subtense bar ! (### Tapes ! !#)###

• Modern Technology echnology::  - Electronic Distance Measuring (EDM) devices: 2 +2 

Tape Measurement  • •

*ccurac& and speed considerations $or ci+il engineers, Sources o$ Errors • • • • • •

-ncorrect length o$ the tape Temperature di$$erence Sag Poor alignment Tape not hori.ontal -mproper Plumbing

Odometer and Subtense Bar  • •

The idea o$ an odometer, Subtense bar a % m rod, •

Distance /0 cot1'%2 m,

 iming Telescoe

 !"u#tense $ar  Distance H % cot( &2) m'

  &2

       H

tan ( &2) % (&2) & H

&2

H % (&2) & tan( &2) *  % 2 m, then H %  & tan ( &2) % cot ( &2)

Example: 

.hat is the horizontal distance #et.een  and $ i the angle  .as 2/

• •

3hapter 1!42 Principle o$ the Stadia • •

Stadia

Horizontal Distance = 100 rod intercept $or a hori.ontal line o$ sight and a +ertical rod S&mbols •  1-2 rod intercept) or stadia inter+al •  1i2 spacing bet5een stadia hair • 1$'i2 0 k 0 !## stadia inter+al $actor • 3 0 1c 6 $2 appro7imatel& #) Stadia constant

D = KI + C = 100 I, for horizontal sight

H = 100 I cos2(α)

V = 100 I sin(α) cos(α)

Electronic Distance Measurement  •

Earl& t&pes

Transmit light) measure up to %" miles • Transmit micro5a+es) measure up to "# miles • 3lassi$ication o$ EDM • Electro8optical laser or in$ra red re$lected $rom passi+e prism or sur$aces) the 9S has installed a prism on the moon, • Micro5a+e t5o positi+e units) :PS replaced them $or most engineering applications such as h&drographic sur+e&s •

Electromagnetic Spectrum

Distance Computation •

•

•

;e onl& measure the phase angle shi$t 1change2 ) di$$erent signals o$ 5a+e length !# !## !### !#)### m are sent, Each $raction pro+ides a digit1s2, (Phase shift / 360)*wave length = non coplete c!cle length"

E7ample ho5 a distance (ects .ill loo? uside do.n, notice the #o1 at the tail o the arro.

Aiming at a rism thro!gh th" t"l"sco" of a total station in a zoo#

Reflectors (Prisms) @ully rotating rism

$rism an% sighting targ"t

• •

* re$lector might include a single prism or a group o$ prisms e$lectors can be a simple re$lecting paper8sticker) the& are called sheet8 prisms) paper prism) or re$lecti+e sheeting, >er& instrumental in construction sites and de$ormation monitoring o$ structures,

EDM Accuracy (mm) and (ppm is the most common, • Estimated error in distance 0 Ei% 6 er % 6 ec% 6 1 pp C D2% • ;here Ei and er are the centering errors o$ the instrument and the re$lector) ec is the constant error o$ the EDM) and PPM is the scalar error o$ the EDM E7ample 48" page !"4 i$ the estimates errors o$ centering the instrument and target 5ere  (mm and  "mm respecti+el&) the EDM had a speci$ied error o$  1%mm 6%ppm2 5hat is the estimated error in measuring =%,(%F mA *ns5er  4,< mm •

•Prism

constant consideration, •Total

station >s EDM,

•Data

collectors,

•Prismless

EDM up to !## m) can reach hard places) $igure 48!