By the end of this chapter, you will be able to:
Mastering these skills will help you take accurate height measurements essential for successful surveying and construction projects.
Surveying height accurately is crucial for land survey professionals as it affects topographical mapping, construction site planning, and boundary demarcation. This chapter focuses on the operation of height measuring instruments, foundational tools that enable surveyors to determine elevations with precision. In the Kenyan context, where diverse terrains from the Rift Valley to coastal plains demand varied surveying approaches, mastery of these instruments ensures reliable data collection for infrastructure development, urban planning, and environmental management. Understanding the different height measuring instruments and their appropriate applications is essential for achieving professional competence in land surveying.
Height measuring instruments are specialized tools designed to measure vertical distances or elevations relative to a datum. For land surveyors in Kenya, selecting the appropriate instrument depends on factors such as terrain, required accuracy, and project scale. This section explores the main height measuring instruments used in surveying, detailing their specifications, operational principles, and typical uses in the field.
Instrument identification means recognising each height measuring instrument and its accessories, knowing how it differs from the others and what work it suits. Height measuring instruments vary from simple manual devices to advanced electronic systems. Below is a table summarizing the primary instruments commonly employed in land surveying:
| Name | Specification | Use |
|---|---|---|
| Dumpy Level | Optical instrument with fixed telescope, 32x magnification, spirit level for horizontal line sighting | Measures height differences and establishes horizontal planes |
| Automatic Level | Self-leveling optical instrument with compensator, 24x to 32x magnification | Facilitates faster leveling by automatically adjusting the line of sight |
| Digital Level | Electronic device with digital readout, accuracy up to ±1 mm per km | Provides precise height measurements with digital data recording |
| Theodolite (with leveling staff) | Optical instrument for measuring vertical and horizontal angles, magnification ~30x | Used for trigonometric leveling and height determination via angular measurements |
| Laser Level | Emits a laser beam to establish a horizontal plane, range varies up to 500 meters | Quick setup for height alignment and site grading tasks |
The Dumpy Level is a traditional instrument widely used in Kenya's county government projects for establishing benchmarks. Its optical system requires manual focusing and leveling using foot screws and a spirit vial. In contrast, the Automatic Level incorporates a pendulum compensator to maintain horizontal sight automatically, reducing operator fatigue and errors during long survey lines in construction sites like those managed by Nairobi City County.
The Digital Level integrates electronic sensors and displays, allowing surveyors at institutions such as the Kenya Forest Service to record precise elevation data efficiently, minimizing transcription errors. The Theodolite, though primarily an angular measuring device, is essential in height measurement when combined with leveling staffs for trigonometric calculations, useful in rugged terrains like those around Mount Kenya National Park.
The Laser Level is increasingly popular in urban developments and road construction where rapid establishment of horizontal reference planes over extensive areas is necessary. Its laser beam offers a visible, highly accurate horizontal line that guides excavations and foundation works.
| Name | Specification | Use |
|---|---|---|
| Telescopic levelling staff | Aluminium, 4 or 5 m, E-pattern graduations in 10 mm | Reading heights with optical levels |
| Bar-coded staff | Bar-code pattern on one face | Automatic reading by digital levels |
| Invar staff | Invar strip in a frame, used with a staff support | Precise and geodetic levelling |
| Staff bubble | Circular bubble fitted to the staff | Holding the staff vertical |
| Change plate (foot plate) | Heavy steel plate with a raised stud | Stable turning point on soft ground |
| Tripod | Wooden or aluminium, adjustable legs | Supporting the level |
| Feature | Dumpy level | Automatic level | Digital level |
|---|---|---|---|
| Levelling of line of sight | Manual, using a tubular bubble and footscrews | Automatic, by compensator after rough levelling | Automatic, by compensator |
| Reading | Read by eye on a graduated staff | Read by eye on a graduated staff | Read electronically from a bar-coded staff |
| Speed | Slow | Faster | Fastest |
| Booking | Manual | Manual | Stored electronically |
| Cost | Low | Moderate | High |
Understanding the operational principles behind height measuring instruments is fundamental for their effective use. These principles govern how the instrument translates physical measurements into reliable height data.
Optical instruments like the Dumpy and Automatic Levels operate by projecting a horizontal line of sight through a telescope fitted with a spirit level. By sighting a graduated leveling staff placed on a point with unknown elevation, the surveyor reads the staff intercept to determine height differences relative to a known benchmark.
Automatic and digital levels feature a compensator, typically a pendulum suspended within the instrument, that maintains the telescope's horizontal alignment despite minor tilts of the instrument base. This mechanism accelerates fieldwork and enhances accuracy by eliminating the need for manual fine leveling.
Digital levels use electronic sensors to detect the position of the leveling staff and convert it into digital signals. These signals are processed and displayed numerically, allowing for rapid readings and electronic storage, which reduces manual recording errors.
Theodolites determine height indirectly by measuring vertical angles from a known point to a target. Using trigonometric formulas, the height difference is computed from the measured angle and horizontal distance, a method advantageous in inaccessible or uneven terrain.
Height difference = horizontal distance × tan (vertical angle)
Laser levels emit a coherent beam of light that establishes a visible horizontal plane. Surveyors use detectors or leveling staffs to detect the laser line, enabling quick and accurate height alignment across a site.
Given: The horizontal distance to the top of a water tower is 80.00 m and the vertical angle measured is 12° 30'.
Height difference = 80.00 × tan 12° 30'
Height difference = 80.00 × 0.2217
Answer: 17.74 m above the instrument's line of sight
Choosing the most suitable height measuring instrument depends on the surveying project's specific requirements and environmental conditions encountered in Kenya.
Projects demanding high precision, such as control levelling and engineering surveys, benefit from digital levels due to their superior accuracy and data recording capabilities. Conversely, preliminary site assessments may rely on automatic or dumpy levels for adequate precision at lower cost.
In rugged or inaccessible areas, trigonometric leveling with theodolites is preferred since direct leveling may be impractical. For example, surveyors mapping escarpments near the Great Rift Valley often employ theodolites combined with total stations.
Large-scale infrastructure projects, such as road construction by county governments, require rapid data collection. Laser levels and automatic levels offer faster setup and measurement cycles, reducing labor time and costs.
While digital and laser levels provide advanced features, their higher acquisition and maintenance costs may limit their use in smaller firms or rural projects. Dumpy levels remain a cost-effective option widely used in public sector projects with constrained budgets.
In areas with frequent dust or rain, instruments with sealed optics and robust construction, such as automatic levels, perform better. For instance, survey teams working in coastal Mombasa must consider humidity and salt air effects on equipment choice.
Create a free account to open more of this chapter.
Free: practical guides, quick cards, workplace scenarios and more.
Create a free accountThis chapter focused on the identification of various height measuring instruments commonly used in surveying, highlighting their specific features and purposes. It then explored the practical operation of these instruments through height measuring exercises, demonstrating how to accurately determine elevation differences in the field. The procedures covered included proper setup, reading measurements, and recording data to ensure precision in surveying tasks. Additionally, the chapter emphasized the importance of regular maintenance of height measuring instruments to preserve their accuracy and extend their service life. Maintenance practices such as cleaning, calibration, and safe storage were discussed to prevent damage and ensure reliable performance. Overall, the chapter provided a comprehensive overview of the tools, techniques, and care necessary for effective height measurement in surveying operations.
At the start of this chapter we promised you would be able to:
Tick each one you can genuinely do.
So, are you there yet?
You're competent when you can confidently do 50% or more of what this chapter promised.
Sign in to record how you're doing.