Geodetic Awareness

Introduction

This page explains why geodetic awareness is important. Further information is contained in IOGP Report 373-01 Geodetic awareness, freely available from IOGP Bookstore. 

Geodetic awareness is essential for operational decision making and to avoid HSE risk because:

1. Most data have locations.
2. Decisions and safe operations rely on the correctness of these locations.
3. Coordinates are meaningless without a Coordinate Reference System (CRS).

Hence, the CRS must always be linked to spatial data. This is made easy by using the EPSG Dataset, because a standard EPSG CRS code can be associated with the coordinates. The process of associating a CRS with coordinates is called geodetic referencing, and this is crucial to make reliable decisions and for safe operations.

Figure 1 - Data layers associated with IOGP Land Survey Data Model. 

Spatial data is unambiguously referenced to a unique location by means of coordinates and a CRS. Coordinates are not measurable absolute quantities like temperature or mass. Instead, coordinates are relative to a chosen starting point.  

A CRS defines this starting point and the axes to which coordinates refer. Coordinates by themselves are not unique. Only together with their CRS do they uniquely define a location. 

When you see coordinates you should always think “from where?” and never make an assumption on the CRS used. 

Before datasets can be merged or co-visualized they need to be transformed into a common CRS so that they align.

Geodetic integrity

Now that we understand that a CRS is required for your data, and that there is a big risk of getting to the wrong location if we do not properly keep track of these critical information (i.e. metadata), we can define geodetic integrity. 

1. That spatial data have coordinates.
2. That these coordinates are associated with a well-defined CRS.
3. That data are accompanied by a history record of checks and operations applied (an audit trial).

The EPSG Dataset facilitates this by utilizing the ISO 19111 standard: Referencing locations by coordinates. This enables and facilitates software interoperability, the exchange of data between applications.

The EPSG Dataset contains definitions of CRS plus transformations and conversions between them.  The Guidance Notes 373-07 series provide users with concise background information, clear definitions (including mathematical formulas), examples, and discussion (available via the menu bar Support Documentation). These reports are intended for end users who seek geodetic information in a specific project area or new working area.

Maintaining geodetic integrity

Once we have achieved geodetic integrity we have to be careful that coordinates remain associated with the correct CRS, and that geodetic engines apply the correct math, while precision is not eroded:

1. Whenever one transfers or stores data in software systems, or applies conversions or transformations to change the CRS.
2. That is done by checking software (refer also to GIGS under "Support Documentation" in menu bar above), guidance notes and work procedures and by raising competences of staff in Industry.

How to avoid geodetic failures?

1. Use an appropriate projected CRS such that calculations in the map plane yield accurate results (e.g., in Wells planning software and geological modeling applications).
2. Consistently use an appropriate coordinate transformation such that datasets can be merged and co-visualized (ideally avoid transformations by acquiring and storing data in the same CRS!).
3. Always show the CRS that is associated with the coordinates and keep track of coordinate operations that have been applied on the data (such that geodetic integrity can be verified by the end user).

Figure 3 - Completeness, correctness, consistency and verifiability are the criteria to pass for geodetic integrity, and the ability for end-users to verify that geodetic integrity is achieved. 

Geospatial Integrity of the Geoscience Software 

The GIGS solution, developed and maintained by IOGP’s Geomatics Committee, was initiated in 2007 in response to significant concern about and documented evidence of geospatial integrity failures in geoscience software. It provides software developers with recommended guidance and good practice regarding geospatial integrity.

Although focused on applications related to the energy industry, GIGS principles and framework can be readily applied to any software or data model that handles spatial data to promote widespread usage and awareness of the importance of geospatial integrity. 

Watch interview with Josh Townsend, Chair of GIGS Expert Group, and learn more about the GIGS project, its benefits to industry, and its success to date. See also IOGP News. 

Geodesy guidance notes

All IOGP geodesy guidance notes are freely available from the IOGP Bookstore.