science

Hellenic Geodetic Reference System 1987

Hellenic Geodetic Reference System 1987 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 Hellenic Geodetic Reference System 1987 rather than just read about it. In short: The Hellenic Geodetic Reference System 1987 or HGRS87 (Greek: Ελληνικό Γεωδαιτικό Σύστημα Αναφοράς 1987 or ΕΓΣΑ'87) is a geodetic system commonly used in Greece (SRID=2100). The system specifies a local geodetic datum and a projection system.

Key takeaways

Hellenic Geodetic Reference System 1987 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hellenic Geodetic Reference System 1987 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hellenic Geodetic Reference System 1987 from memory before moving on to harder problems.

Reference excerpt

The Hellenic Geodetic Reference System 1987 or HGRS87 (Greek: Ελληνικό Γεωδαιτικό Σύστημα Αναφοράς 1987 or ΕΓΣΑ'87) is a geodetic system commonly used in Greece (SRID=2100). The system specifies a local geodetic datum and a projection system. In some documents it is called Greek Geodetic Reference System 1987 or GGRS87.

HGRS87 datum HGRS87 specifies a non-geocentric datum that is tied to the coordinates of the key geodetic station at the Dionysos Satellite Observatory (DSO) northeast of Athens (38.078400°N 23.932939°E / 38.078400; 23.932939). The central pedestal (CP) at this location has by definition HGRS87 coordinates 38° 4' 33.8000" N - 23° 55' 51.0000"E, N = +7 m. Although HGRS87 uses the GRS80 ellipsoid, the origin is shifted relative to the GRS80 geocenter, so that the ellipsoidal surface is best for Greece. The specified offsets relative to WGS84 (WGS84-HGRS87) are: Δx = -199.87 m, Δy = 74.79 m, Δz = 246.62 m. The HGRS87 datum is implemented by a first order geodetic network, which consists of approximately 30 triangulation stations throughout Greece and is maintained by the Hellenic Military Geographical Service. The initial uncertainty was estimated as 0.1 ppm (1 × 10−7). However, there are considerable tectonic movements that move parts of Greece towards different directions, causing incompatibilities between surveys taking place at different times. HGRS87 replaced an earlier de facto geodetic system. The datum of that system was based on the Bessel ellipsoid, with an accurate determination of the geodetic coordinates at the central premises of the National Observatory of Athens 37° 58' 20.1" N - 23° 42' 58.5"E with current Google Earth TM coordinates:37° 58' 20.20" N - 23° 43' 05.36"E and supplemented by an accurately measured azimuth from the observatory to Mount Parnes. Cartographic projections for civilian use were based on the Hatt projection system, with different projection parameters for each 1:100000 map.

HGRS87 projection HGRS87 also specifies a transverse Mercator cartographic projection (TM) with m0=0.9996, covering six degrees of longitude either side of 24 degrees east (18-30 degrees east). This way all Greek territory (stretching to approximately 9° of longitude) is projected in one zone. References are in meters. Northings are counted from the equator. A false easting of 500000 m is assigned to the central meridian (24° east), so eastings are always positive. Conversion from geographical coordinates in GRS80 to a projection in HGRS87 is supported by PROJ with appropriate parameters. The conversion is performed with the following code (shell command line):

Migration to HTRS07 While HGRS87 is still widely used for most civilian uses, it is partly replaced by the new Hellenic Terrestrial Reference System 2007 or HTRS07 (SRID=96758). HTRS07, which was specified for the Hellenic Positioning System (HEPOS) project, is GPS based and is compatible with European Terrestrial Reference System 1989 (ETRS89). HTRS07 is currently used for the cadastral surveys.

Converters SurvoGR online converter (updated 2023) Online conversion among WGS84 / EGSA87 / HRTS07 / HATT (THEMOS SA) Matlab & C functions converting between WGS84 / EGSA87

See also Hellenic Military Geographical Service

References

Further reading Συντεταγμένες ΕΓΣΑ’87 σε δέκτες GPS Programming popular GPS receivers to display coordinates using the HGRS87 datum (in Greek). Coordinate Reference Systems GR Map Projections GR Mitsakaki, C., Agatza-Balodimou, A.M., Papazissi, K. (July 2006). "Geodetic reference frames transformations". Survey Review. 38 (301). Maney Publishing: 608–618. doi:10.1179/003962606780732092.{{cite journal}}: CS1 maint: multiple names: authors list (link) G. Veis (1987). The Hellenic Geodetic Reference System (Greek: Το Ελληνικό Γεωδαιτικό Σύστημα Αναφοράς) (PDF). Athens, Greece: Hellenic Mapping & Cadastral Organization (HEMCO).{{cite book}}: CS1 maint: deprecated archival service (link)

Illustrations

Worked examples

Example 1 — a first encounter with Hellenic Geodetic Reference System 1987

Start with the simplest possible case. Write down what Hellenic Geodetic Reference System 1987 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 Hellenic Geodetic Reference System 1987 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 Hellenic Geodetic Reference System 1987 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 Hellenic Geodetic Reference System 1987

In research: Hellenic Geodetic Reference System 1987 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 Hellenic Geodetic Reference System 1987 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: Hellenic Geodetic Reference System 1987 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geodesy, Geographic coordinate systems, so understanding it makes those chapters shorter.
In everyday life: Look for Hellenic Geodetic Reference System 1987 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 Hellenic Geodetic Reference System 1987 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hellenic Geodetic Reference System 1987 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 Hellenic Geodetic Reference System 1987 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hellenic Geodetic Reference System 1987 in simple terms?

Why does Hellenic Geodetic Reference System 1987 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 Hellenic Geodetic Reference System 1987?

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 Hellenic Geodetic Reference System 1987.