DEFINITIONS

 DEFINITIONS 

Elevation: a point's vertical distance above or below a surface of reference (datum) - that could be a first floor elevation of multi-story building on architectural plans, flat surface used as reference, as the basis of measuring elevation. it could be mean sea level. - we called that surface of reference - datum.

Datum - surface of reference. most common datum is MSL (mean sea level), geoid 88 etc

Level surface - A level line is a curved line, normal at all points to a plumb line. 

LEVELING - determining the elevation of a point or the difference in elevation between points.

Level Circuit - series of leveling measurements used to determinate the elevation of one or more points.

Backsight (BS)- is one of those leveling measurements , rod reading at a point of known elevation

Foresight (FS) - rod reading at a point of unknown elevation 

we use these at least pairs for every backsight we typically have at least one foresight

Level - instrument

HI Height of Instrument : elevation of level crosshair (line of sight). horizontal crosshair sweeps trough horizontal plane and that horizontal plane is one to which we give an elevation. thats is HI. from that elevation , from that reference elevation, we can calculate elevations for unknown points

Turning Point - a point temporarily used to transfer an elevation ( forward in the circuit) (მაგ. 300 მეტრი ჩანს როდზე და 2 კმა ელევაციის გასაყვანი)

Benchmark - a relatively permanent object with a marked point of known elevation

Benchmark Circuit - level circuit to performed to establish elevations of new benchmarks (like for construction layout purposes) typical to new projects.

1 BS and 1 FS for each instrument setup 

at profile view we can see we start at BM 352 and then use 2 TPs to move us forward two measurements on to BM 358A which in this case is unknown point and then we through turning point 3 run our circuit back to our starting point - BM 352. 

the plan view indicates that the route we take go on out to benchmark 358A and coming back don't have to necessarily be the same.

every setup where you see the instrument symbols  shows BS and FS, thus every reading here has a potential impact on the final computed elevation of benchmark 352.  352 has its known elevation but our series of circuit measurements may yield a different computed elevation. every BS and FS in this circuit is on the loop and has direct impact on the closure error in this circuit.

Profile Circuit - level circuit performed to measure multiple foresights per setup. 

One BS and multiple FS for each instrument setup

(majority of level circuits in mapping and construction) so for every BS and every setup we can have multiple FSs , everyone of those foresights per setup is measured from the same HI.

***

consider a circuit that has 3 setups and it going from BM 100 to BM 200 .we see an instrument that has taken a backsight on benchmark 100 with a reading of 7.17 and turning point on the right with reading 3.02. the other readings perhaps are taken on the ground along the centerline of some lets say street centerline. well , those readings are not a part of the loop we called them side shots, they arnt checked by any other reading, they are simply independent from the loop. you could say even addition to what you might consider a basic benchmark loop.

 in the previous picture we had 1 BS and 4 FS, here we have 1 BS on turning point to establish the HIV instrument and then 4 FS. one of those foresights is the FS on TP2 and other FSs are side shots on this profile circuit.

and on 3rd setup - 1 BS on TP2 followed by 3 FS, 2 of them are side shots and the final shot is a FS closing on to benchmark 200.

Loop Circuit , we also have loop circuits. If you start a BM or level circuit and end it in the same place we'd call it a loop circuit. you start from known elevation > unknown elevation>unknow elevation>back to known elevation. 

Connecting circuit is when u start from known elevation > unknown > another known.