science

Vertical Offshore Reference Frames

Vertical Offshore Reference Frames is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Vertical Offshore Reference Frames rather than just read about it. In short: Vertical Offshore Reference Frames (VORF) is a set of high resolution surface models, published and maintained by the UK Hydrographic Office, which together define a vertical datum for hydrographic surveying and charting in the United Kingdom and Ireland. Tidal surface models The following tidal and sea level surfaces are included: Chart Datum (CD) Lowest Astronomical Tide (LAT) Mean Sea Level (MSL) Mean Low Water S…

Key takeaways

Vertical Offshore Reference Frames belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Vertical Offshore Reference Frames to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Vertical Offshore Reference Frames from memory before moving on to harder problems.

Reference excerpt

Vertical Offshore Reference Frames (VORF) is a set of high resolution surface models, published and maintained by the UK Hydrographic Office, which together define a vertical datum for hydrographic surveying and charting in the United Kingdom and Ireland.

Tidal surface models The following tidal and sea level surfaces are included:

Chart Datum (CD) Lowest Astronomical Tide (LAT) Mean Sea Level (MSL) Mean Low Water Springs (MLWS) Mean High Water Springs (MHWS) Highest Astronomical Tide (HAT) Land datums including Ordnance Datums Newlyn, Belfast and Poolbeg The surfaces are modelled with respect to the terrestrial reference frame used for satellite navigation (GNSS) positioning, ETRS89. Thus VORF directly permits the use of high precision GNSS in hydrographic survey, and also allows the capability of transforming vertical data between the different datums. The UK Maritime & Coastguard Agency requires the use of VORF for tidal reductions as part of its civil hydrography programme.

Files A main product of the VORF project was the gridded vertical correction files which deliver the capability to transfer heights and depths from one vertical reference system to another, "allowing the direct use of depth data from surveys which is referred to a WGS84 compatible datum rather than Chart Datum and thus enabling Hydrographic surveyors to survey without the need to measure tides". This is accomplished via a set of files, each file containing a grid of height corrections to apply to GNSS-derived heights to translate them to one of several VORF models. There is higher resolution in estuaries and inlets, but for most of the areas covered, there is a single height correction for each roughly 900 by 500 metre rectangle. VORF correction files are purchased from the same source as Admiralty charts.

Format The Admiralty provides VORF data in the form of ".vrf" files, each of which contains data representing the separation between a given pair of datums. The filename indicates the VORF model version, the south-west corner of the area covered, and the pair of datums it represents. The files can be bought and downloaded from the Admiralty Marine Data Portal, and are in plain text (ASCII) format, so can be viewed in any standard text editor. They contain a list of positions forming a regular grid. At each position the separation between the datums is given, and the uncertainty in this value. Positions are in decimal degrees and separation and uncertainty are in metres. The grid resolution is 0.008° over the majority of the VORF area, which corresponds to boxes of approximately 900 x 500 metres. There is higher resolution (typically 0.002° to 0.0005°) around rivers and estuaries, and around Portland Bill. Where a file contains higher-resolution data, the high-resolution values are at the end of the file.

Pricing The data are sold by the "block", with a VORF block covering an area of 0.088° latitude by 0.16° longitude. This makes each block about a 10 kilometre square (96 square kilometres), containing about 220 data points. The price (as at July 2021) starts at £216 per block, with discounts for quantity.

Use The VORF datum surfaces will generally be used by automated survey software, and for this purpose, it may be necessary to rearrange the data to create a suitable input file for the software in question. For example, software packages EIVA Navipac and Qinsy require specialised procedures.

Development history The VORF project ran from 2005 as a collaborative research project, sponsored by the UKHO, with a consortium comprising Proudman Oceanographic Laboratory, DTU, and led by University College London. It was delivered to the UKHO in 2008. VORF was developed using satellite altimetry, tide gauge observations, geoid and tidal modelling, and GNSS observations. VORF meets its target inshore accuracy of 10 cm in most of the domain of applicability.

See also Admiralty chart – Nautical chart Hydrography – Measurement of bodies of water Hydrographic survey – Science of measurement and description of features which affect maritime activities Nautical chart – Topographic map of a maritime area and adjacent coastal regions

References

Illustrations

Worked examples

Example 1 — a first encounter with Vertical Offshore Reference Frames

Start with the simplest possible case. Write down what Vertical Offshore Reference Frames claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Vertical Offshore Reference Frames before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Vertical Offshore Reference Frames ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Vertical Offshore Reference Frames

In research: Vertical Offshore Reference Frames appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Vertical Offshore Reference Frames in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Vertical Offshore Reference Frames is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cartography, Geodetic datums, Nautical charts, so understanding it makes those chapters shorter.
In everyday life: Look for Vertical Offshore Reference Frames outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Vertical Offshore Reference Frames in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Vertical Offshore Reference Frames means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Vertical Offshore Reference Frames out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Vertical Offshore Reference Frames in simple terms?

Why does Vertical Offshore Reference Frames matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Vertical Offshore Reference Frames?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Vertical Offshore Reference Frames.