science

Well-known text representation of coordinate reference systems

Well-known text representation of coordinate reference systems 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 Well-known text representation of coordinate reference systems rather than just read about it. In short: Well-known text representation of coordinate reference systems (WKT or WKT-CRS) is a text markup language for representing spatial reference systems and transformations between spatial reference systems. The formats were originally defined by the Open Geospatial Consortium (OGC) and described in their Simple Feature Access and Well-known text representation of coordinate reference systems specifications.

Key takeaways

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

Reference excerpt

Well-known text representation of coordinate reference systems (WKT or WKT-CRS) is a text markup language for representing spatial reference systems and transformations between spatial reference systems. The formats were originally defined by the Open Geospatial Consortium (OGC) and described in their Simple Feature Access and Well-known text representation of coordinate reference systems specifications. The current standard definition is ISO 19162:2019, which supersedes version ISO 19162:2015.

Version history This WKT format was initially defined by the Open Geospatial Consortium (OGC) in 1999, then extended in 2001. This format, also defined in ISO 19125-1:2004, is sometime known as "WKT 1". Later, evolution of the Coordinate Reference System conceptual model, new requirements and inconsistencies in implementation of WKT 1 format between different software have encouraged the revision of that format. The updated "Well-known text representation of coordinate reference systems" standard, sometime known as "WKT 2", was adopted by the Open Geospatial Consortium in 2015. This standard is published conjointly by the International Organization for Standardization as ISO 19162:2015. Confusingly, the original 2015 "WKT 2" standard has a version number 1 for the new, stricter WKT-CRS specification. A newer revision called WKT-CRS 2 was published in 2018, with the ISO version being ISO 19162:2019.

Backward compatibility A software capable to read coordinate reference systems in WKT 2 format can also read many (but not all) equivalent systems in WKT 1 format. Some caveats exist, notably the removal of the TOWGS84 element which is replaced by the BOUNDCRS element. Another caveat is about the units of measurement. Some of them were unspecified in oldest WKT 1 specifications (for example the PRIMEM unit), which has led to different interpretations by different software. Those units of measurement have been clarified in the 2001 update and the WKT 2 specification is consistent with that clarification. But not all software has followed the 2001 clarification.

ESRI vs OGC Esri, which also participated in writing the WKT 2 specification, had a few variations on OGC's WKT 1 specification, making it stricter and contain less ambiguities. As a result, some databases differentiate between "OGC WKT" and "ESRI WKT" representations. The problem is largely resolved in WKT 2, as it is better-defined. One distinction is that it does not have TOWGS84, much like WKT 2.

Coordinate reference systems WKT can describe coordinate reference systems. For example, the WKT below describes a two-dimensional geographic coordinate reference system with a latitude axis first, then a longitude axis. The coordinate system is related to Earth by the WGS84 geodetic datum:

The WKT format can describe not only geographic coordinate reference systems, but also geocentric, projected, vertical, temporal and engineering ones (for example a coordinate reference system attached to a boat). The standard describes how to combine those coordinate reference systems together.

Coordinate operations A WKT format is defined to describe the operation methods and parameters used to convert or transform coordinates between two different coordinate reference systems. The WKT 1 and WKT 2 formats are incompatible regarding coordinate operations, because of differences in the modelling. Below is an example of a concatenation of two WKT 1 transformation descriptions, where the Mercator projection is applied first and then an affine transform is applied on the result:

Below is an example of a datum shift operation in WKT 2 format. Contrarily to an equivalent description in WKT 1 format, the WKT 2 description specifies the source and target coordinate reference systems, together with the domain of validity and the accuracy (in metres) that we can expect from this operation:

APIs that provide support Apache Spatial Information System: parses and formats WKT versions 1 and 2 for coordinate reference systems and coordinate operations PROJ

See also Well-known text representation of geometry

References

External links Coordinate Transformation Service Specification OGR projection tutorial Spatial reference system well-known text format version 1 Archived 2019-01-24 at the Wayback Machine Spatial reference system well-known text format version 2 ISO Spatial standard (there is a charge for this)

Worked examples

Example 1 — a first encounter with Well-known text representation of coordinate reference systems

Start with the simplest possible case. Write down what Well-known text representation of coordinate reference systems 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 Well-known text representation of coordinate reference systems 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 Well-known text representation of coordinate reference systems 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 Well-known text representation of coordinate reference systems

In research: Well-known text representation of coordinate reference systems 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 Well-known text representation of coordinate reference systems 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: Well-known text representation of coordinate reference systems is common in secondary-school and first-year university syllabi. It links to neighbouring topics GIS file formats, Map projections, Markup languages, so understanding it makes those chapters shorter.
In everyday life: Look for Well-known text representation of coordinate reference systems 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 Well-known text representation of coordinate reference systems in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Well-known text representation of coordinate reference systems 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 Well-known text representation of coordinate reference systems out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Well-known text representation of coordinate reference systems in simple terms?

Why does Well-known text representation of coordinate reference systems 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 Well-known text representation of coordinate reference systems?

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 Well-known text representation of coordinate reference systems.