In this edition of Buckton’s newsletter, we will dive deep into the complexities and importance of Vertical Datums.
We're so glad you're here!
Got questions? Don't hesitate to get in touch!
Happy reading!
Welcome to the latest edition of Buckton’s newsletter, where we dive deep into the complexities and importance of vertical datums, focusing particularly on the New Zealand Vertical Datum 2016 (NZVD2016). In this issue, we'll explore the fundamental concept of a vertical datum, review historical practices involving Mean Sea Level (MSL), and introduce the cutting-edge features of the NZVD2016.
Understanding vertical datums is crucial for anyone involved in land development, surveying, or any field requiring precise elevation measurements. This newsletter aims to clarify these technical concepts and demonstrate their impact on practical applications.
What is a Vertical Datum?
The height of a point is its distance above either a reference point or the surface of a vertical datum.
Historically, what have we used?
Mean Sea Level (MSL)
Sea level varies around the coast and is affected by weather, atmospheric pressure, currents, and tidal forces - it's neither flat nor consistent.
For sea surfaces, the reference point was established by measuring sea level at reference tide gauges over time.
It depends on gravity from the sun and moon, requiring over 18 years of observations to measure a full tidal cycle.
The base of a local vertical datum is a snapshot in time. Mean sea level (MSL) is not the same as a local vertical datum (LVD).Auckland Council's reasoning behind this scheme is to offer incentives for rural property owners to forego development on their properties by enabling them to sell a title right, which is used in a Countryside Living zone which is typically located on the fringe of urban areas, closer to appropriate infrastructure, and maintaining rural areas for productive purposes, not lifestyle purposes.
Local Vertical Datum (LVD)
New Zealand has 13 official local vertical datums (LVDs) and various other regional
datums established as needed.
These were set by estimating mean sea level (MSL) and spreading this across a benchmark network.
Most LVDs were established between 1940 and 1990 using pre-1960 MSL values. Despite potential shifts, Toitū Te Whenua has not regularly updated these heights since their initial measurement.
Local Vertical Datum Constraints...
Long, linear, poorly constrained networks
Restricted to roads.
Accuracy assessed on an observation basis
Errors propagate.
No relative assessment of marks not observed.
Benchmarks move
Difficult to tell if a benchmark is disturbed.
Absolute accuracy is unknown.
Key Features of NZVD2016:
Geoid-based Datum - NZVD2016 is a geoid-based vertical datum, meaning it uses the geoid model to represent the shape of the Earth's gravity field. This provides a more accurate reference for height measurements compared to earlier datums that relied on sea-level measurements.
Improved Accuracy - NZVD2016 incorporates the latest geoid model developed using satellite gravity data, ground gravity measurements, and other geodetic observations. This results in more accurate height measurements across New Zealand, especially in areas far from the coast.
Uniform Reference - The adoption ensures that height measurements are consistent across New Zealand, replacing earlier regional datums that were often based on local mean sea levels at different tide gauges.
Compatibility with Modern Technologies - NZVD2016 is designed to be compatible with modern positioning technologies like GNSS (Global Navigation Satellite Systems), making it easier for users to obtain accurate elevation data using GPS and similar tools.
What is a Geoid?
A Geoid, which is shaped like a slightly squashed ball, gives a hypothetical global mean sea level surface, or a quasigeoid that provides a simplified version that is suitable for most applications.
For New Zealand Vertical Datum 2016, the reference surface is New Zealand Quasigeoid 2016.
An ellipsoid is a mathematically defined, smooth, three-dimensional shape that closely approximates the shape of the Earth.
Issues That May Arise:
(Working on projects with different datums)
Why do we Need NZVD2016?
Surveying and Mapping - Provides a uniform reference for surveying and mapping activities throughout New Zealand.
Engineering and Construction - Ensures consistent height data for engineering and construction projects, such as road building and flood risk assessment.
Environmental Monitoring - Supports accurate monitoring of sea level changes, land subsidence, and other environmental factors.
How Can Buckton Surveyors and Planners Help You?
Our local knowledge, years of experience, and our ability to use leading-edge technology combine to deliver the best outcomes.
We are committed to our clients and their projects. We will instantly engage with the vision you have for your land. We turn potential into reality!
Kommentarer