252:
206:
focused until the level staff is plainly visible in the crosshairs. In the case of a high accuracy manual level, the fine level adjustment is made by an altitude screw, using a high accuracy bubble level fixed to the telescope. This can be viewed by a mirror whilst adjusting or the ends of the bubble can be displayed within the telescope, which also allows assurance of the accurate level of the telescope whilst the sight is being taken. However, in the case of an automatic level, altitude adjustment is done automatically by a suspended prism due to gravity, as long as the coarse levelling is accurate within certain limits. When level, the staff graduation reading at the crosshairs is recorded, and an identifying mark or marker placed where the level staff rested on the object or position being surveyed.
317:
210:
This gives the height of the instrument above the starting (backsight) point and allows the height of the instrument (H.I.) above the datum to be computed. The rod is then held on an unknown point and a reading is taken in the same manner, allowing the elevation of the new (foresight) point to be computed. The difference between these two readings equals the change in elevation, which is why this method is also called
1002:, while surveying the route of a proposed railway line from London to Dover. More compact and hence both more robust and easier to transport, it is commonly believed that dumpy levelling is less accurate than other types of levelling, but such is not the case. Dumpy levelling requires shorter and therefore more numerous sights, but this fault is compensated by the practice of making foresights and backsights equal.
49:
198:
214:. The procedure is repeated until the destination point is reached. It is usual practice to perform either a complete loop back to the starting point or else close the traverse on a second point whose elevation is already known. The closure check guards against blunders in the operation, and allows residual error to be distributed in the most likely manner among the stations.
108:
183:, and the telescope can freely rotate 360° in a horizontal plane. The surveyor adjusts the instrument's level by coarse adjustment of the tripod legs and fine adjustment using three precision levelling screws on the instrument to make the rotational plane horizontal. The surveyor does this with the use of a
504:
1022:
The surveyor sets the instrument up quickly and does not have to re-level it carefully each time they sight on a rod on another point. It also reduces the effect of minor settling of the tripod to the actual amount of motion instead of leveraging the tilt over the sight distance. Because the level of
674:
For precise work these effects need to be calculated and corrections applied. For most work it is sufficient to keep the foresight and backsight distances approximately equal so that the refraction and curvature effects cancel out. Refraction is generally the greatest source of error in leveling. For
1037:
Laser levels project a beam which is visible and/or detectable by a sensor on the leveling rod. This style is widely used in construction work but not for more precise control work. An advantage is that one person can perform the levelling independently, whereas other types require one person at the
238:
To "turn" the level, one must first take a reading and record the elevation of the point the rod is located on. While the rod is being kept in exactly the same location, the level is moved to a new location where the rod is still visible. A reading is taken from the new location of the level and the
1005:
Precise level designs were often used for large leveling projects where utmost accuracy was required. They differ from other levels in having a very precise spirit level tube and a micrometer adjustment to raise or lower the line of sight so that the crosshair can be made to coincide with a line on
242:
The level must be horizontal to get a valid measurement. Because of this, if the horizontal crosshair of the instrument is lower than the base of the rod, the surveyor will not be able to sight the rod and get a reading. The rod can usually be raised up to 25 feet high, allowing the level to be set
225:
The two main types of levelling are single-levelling as already described, and double-levelling (double-rodding). In double-levelling, a surveyor takes two foresights and two backsights and makes sure the difference between the foresights and the difference between the backsights are equal, thereby
1018:
that ensures that the line of sight remains horizontal once the operator has roughly leveled the instrument (to within maybe 0.05 degree). The compensator consists of small prisms suspended from wires inside of the level's chassis that are connected together in the shape of a pendulum. This allows
234:
When using an optical level, the endpoint may be out of the effective range of the instrument. There may be obstructions or large changes of elevation between the endpoints. In these situations, extra setups are needed. Turning is a term used when referring to moving the level to take an elevation
209:
A typical procedure for a linear track of levels from a known datum is as follows. Set up the instrument within 100 metres (110 yards) of a point of known or assumed elevation. A rod or staff is held vertical on that point and the instrument is used manually or automatically to read the rod scale.
205:
The surveyor looks through the eyepiece of telescope while an assistant holds a vertical level staff which is graduated in inches or centimeters. The level staff is placed vertically using a level, with its foot on the point for which the level measurement is required. The telescope is rotated and
336:
meaning an elevation change of approximately 9.30 feet in elevation between Points A and B. So if Point A is at 1,000 feet of elevation, then Point B would be at approximately 1,009.30 feet of elevation, as the reference line (0°) for zenith angles is straight up going clockwise one complete
351:
The curvature of the earth means that a line of sight that is horizontal at the instrument will be higher and higher above a spheroid at greater distances. The effect may be insignificant for some work at distances under 100 meters. The increase in height of a straight line with distance
1023:
the instrument only needs to be adjusted once per setup, the surveyor can quickly and easily read as many side-shots as necessary between turns. Three level screws are used to level the instrument, as opposed to the four screws historically found in dumpy levels.
221:
measurement of the foresight and backsight distances. These also allow use of the average of the three readings (3-wire leveling) as a check against blunders and for averaging out the error of interpolation between marks on the rod scale.
362:
754:
around a loop. In the real gravity field of the Earth, this happens only approximately; on small loops typical of engineering projects, the loop closure is negligible, but on larger loops covering regions or continents it is not.
669:
160:. The cross hairs are used to establish the level point on the target, and the stadia allow range-finding; stadia are usually at ratios of 100:1, in which case one metre between the stadia marks on the
251:
337:
revolution, and so an angle reading of less than 90 degrees (horizontal or flat) would be looking uphill and not down (and opposite for angles greater than 90 degrees), and so would gain elevation.
830:
589:
926:
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68:
956:
860:
499:{\displaystyle {\sqrt {D^{2}+R^{2}}}-R\approx {\frac {D^{2}}{2R}}\approx 0.0785{\text{ m}}(D{\text{ in km}})^{2}\approx 0.0239{\text{ ft}}(D/1000{\text{ ft}})^{2}}
594:
1255:
239:
height difference is used to find the new elevation of the level gun. This is repeated until the series of measurements is completed.
1286:
1197:
1148:
1278:
675:
short level lines the effects of temperature and pressure are generally insignificant, but the effect of the temperature gradient
1336:
965:
High precision levelling, especially when conducted over long distances as used for the establishment and maintenance of
771:
525:
1064:
872:
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for only horizontal light rays to enter, even in cases where the telescope of the instrument is not perfectly plumb.
1346:
1331:
697:
281:, which is preferred when levelling "out" to a number of points from one stationary point. This is done by using a
35:
1183:
1134:
201:
Diagram showing relationship between two level staff, or rods, shown as 1 and 3. The level line of sight is 2.
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1054:
290:
513:
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1069:
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328:) and a slope distance of 305.50 feet not factoring rod or instrument height would be calculated thus:
984:
346:
1311:
324:
Ex: an instrument at Point A reading to a rod at Point B a zenith angle of < 88°15'22" (degrees,
310:
185:
1116:
1341:
1079:
691:
field were completely regular and gravity constant, leveling loops would always close precisely:
179:
688:
316:
866:. For precise leveling networks on a national scale, the latter formula should always be used.
1305:
1282:
1251:
1193:
1144:
516:. The change of air density with elevation causes the line of sight to bend toward the earth.
88:
1223:
1084:
64:
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1140:
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512:
The line of sight is horizontal at the instrument, but is not a straight line because of
1110:
226:
reducing the amount of error. Double-levelling costs twice as much as single-levelling.
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325:
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112:
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96:
42:
197:
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162:
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84:
277:
The other standard method of levelling in construction and surveying is called
302:
664:{\displaystyle \Delta h_{feet}=0.021\left({\frac {D_{ft}}{1000}}\right)^{2}}
313:
must be taken into account in the measurements as well (see section below).
258:
153:
72:
31:
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52:
A wooden tripod holding an optical level is set up firmly on the ground.
17:
1041:
The sensor can be mounted on earth-moving machinery to allow automated
519:
The combined correction for refraction and curvature is approximately:
266:
80:
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270:
76:
1172:
Davis, Foote, and Kelly, Surveying Theory and
Practice, 1966 p. 152
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should be used in all computations, producing geopotential values
315:
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250:
196:
106:
47:
1312:
E-Learning-site with online-exercise for differential levelling
107:
75:, the object of which is to establish or verify or measure the
79:
of specified points relative to a datum. It is widely used in
41:"Spirit levelling" redirects here. For the bubble level, see
289:
to the rod, and the change in elevation is calculated using
293:(see example below). At greater distances (typically 1,000
99:
to measure height differences of construction artifacts.
217:
Some instruments provide three crosshairs which allow
937:
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111:Stadia marks on a crosshair while viewing a metric
1248:Elementary Surveying: An Introduction to Geomatics
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498:
1225:Glossary of Mapping, Charting, and Geodetic Terms
825:{\displaystyle \sum _{i=0}^{n}\Delta h_{i}g_{i},}
584:{\displaystyle \Delta h_{meters}=0.067D_{km}^{2}}
1006:the rod scale and no interpolation is required.
921:{\displaystyle \Delta W_{i}=\Delta h_{i}g_{i}\ }
152:, which consists of a precision telescope with
123:mm; the distance between those two marks is 155
1112:Leveling: Barometric, Trigonometric and Spirit
1228:. U.S. Government Printing Office. p. 98
1222:United States. Department of Defense (1973).
744:{\displaystyle \sum _{i=0}^{n}\Delta h_{i}=0}
8:
862:stands for gravity at the leveling interval
177:The complete unit is normally mounted on a
1250:(13th ed.). Pearson. pp. 90–91.
261:using a Leica TPS1100 total station on an
127:mm, yielding a distance to the rod of 15.5
1317:Differential levelling online calculation
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683:Levelling loops and gravity variations
320:Formulation of trigonometric levelling
285:, or any other instrument to read the
243:much higher than the base of the rod.
1308:Differential leveling video tutorials
332:cos(88°15'22")(305.5)≈ 9.30 ft.,
7:
1038:instrument and one holding the rod.
509:where R is the radius of the earth.
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115:or staff. The top mark is at 1,500
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189:built into the instrument mount.
235:shot from a different location.
1279:Springer Science+Business Media
1274:Dictionary of Civil Engineering
1014:Automatic levels make use of a
758:Instead of height differences,
34:technique. For other uses, see
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119:mm and the lower is at 1,345
1115:. D. Van Nostrand. p.
1065:Glossary of levelling terms
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982:
344:
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36:Levelling (disambiguation)
30:This article is about the
29:
1246:Ghilani, Charles (2010).
1109:Ira Osborn Baker (1887).
287:vertical, or zenith angle
1188:(4th ed.). Oxford:
341:Refraction and curvature
174:metres from the target.
69:see spelling differences
1055:Astrogeodetic levelling
765:do close around loops:
326:minutes, seconds of arc
291:trigonometric functions
279:trigonometric levelling
247:Trigonometric levelling
1271:John S. Scott (1992).
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514:atmospheric refraction
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299:curvature of the Earth
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212:differential levelling
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1337:Geomatics engineering
1070:Hydrostatic levelling
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951:{\displaystyle W_{i}}
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855:{\displaystyle g_{i}}
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345:Further information:
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1182:Guy Bomford (1980).
1133:Guy Bomford (1980).
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1347:Vertical position
1332:Civil engineering
1257:978-0-13-255434-3
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136:Optical levelling
103:Optical levelling
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43:Spirit level
1090:Survey camp
1033:Laser level
1027:Laser level
1016:compensator
996:dumpy level
979:Instruments
763:differences
443: in km
163:level staff
87:to measure
85:cartography
1326:Categories
1232:2023-09-11
1096:References
960:benchmarks
303:refraction
301:, and the
154:crosshairs
1342:Surveying
893:Δ
877:Δ
797:Δ
777:∑
723:Δ
703:∑
599:Δ
530:Δ
457:≈
425:≈
400:≈
394:−
193:Procedure
95:, and in
73:surveying
57:Levelling
32:surveying
1049:See also
958:for the
483: ft
464: ft
263:Iron Age
61:leveling
18:Leveling
1208:Geodesy
1185:Geodesy
1159:Geodesy
1136:Geodesy
1043:grading
677:dT / dh
432: m
267:Ytterby
81:geodesy
1285:
1254:
1196:
1147:
916:
835:where
460:0.0239
428:0.0785
271:Sweden
259:survey
219:stadia
180:tripod
172:
129:
125:
121:
117:
77:height
624:0.021
561:0.067
1283:ISBN
1252:ISBN
1205:See:
1194:ISBN
1156:See:
1145:ISBN
994:The
647:1000
479:1000
356:is:
307:wave
295:feet
166:(or
156:and
142:and
83:and
1117:126
591:or
311:air
168:rod
59:or
1328::
1277:.
1119:.
1045:.
975:.
269:,
131:m.
67:;
1291:.
1260:.
1235:.
1211:.
1202:.
1162:.
1153:.
944:i
940:W
911:i
907:g
901:i
897:h
890:=
885:i
881:W
864:i
848:i
844:g
820:,
815:i
811:g
805:i
801:h
792:n
787:0
784:=
781:i
739:0
736:=
731:i
727:h
718:n
713:0
710:=
707:i
657:2
652:)
642:t
639:f
635:D
629:(
621:=
616:t
613:e
610:e
607:f
603:h
577:2
572:m
569:k
565:D
558:=
553:s
550:r
547:e
544:t
541:e
538:m
534:h
492:2
488:)
475:/
471:D
468:(
452:2
448:)
439:D
436:(
419:R
416:2
410:2
406:D
397:R
387:2
383:R
379:+
374:2
370:D
354:D
273:.
63:(
45:.
38:.
20:)
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