August 22, 2023

Updates in GeoCalc SDK v9.1

Written by: Sam Knight


As the world of geodetics marches steadily into the future, many recent developments have concentrated heavily on historically complete definitions and methods. In the latest release of the GeoCalc SDK, version 9.1, Blue Marble focused on modern topics, such as dynamic reference frames and updates to support the latest national coordinate systems worldwide. In this blog, we will explore some of the things visible in GeoCalc SDK 9.1 and further groundwork for future developments.

Canadian BYN Geoid Grids

A new natively supported geoid transformation in GeoCalc 9.1 is the BYN format. Natural Resources Canada uses geoid grids in this format for the CGVD vertical datum of various epochs and combinations of target systems. One of the unique things about geoid transformations, in general, is that no one standard grid format has taken over in terms of common use and popularity around the world. In the realm of horizontal transformations, there have been a few common standards used worldwide; notably, the NTv2 grid file standard created by the Canadian government for transformations between NAD27 and NAD83. NTv2 grids have since become very common, with many other governments around the planet adopting the use of this format.

Presently, vertical transformations do not have a clear standard. Almost every geoid in the database has a unique grid type in which its data is stored. The formats for storing geoid grid data are chosen individually by the survey authority for the country where the data applies, and extremely few share a common data format. To implement geoid grids in GeoCalc, it was often simpler to restructure the data into an internal format that was already supported. 

Then along came BYN, with several additional grid tables being published, handling many iterations of transformations for the Canadian Vertical Geoid of 2013 and the CVGD 2013a variants. Now, enough new grids are using the BYN format that it simply made sense to add support for the file format itself, such that when new grids are published in the future, GeoCalc SDK users will be able to add them without needing to update their GeoCalc SDK libraries.

New Zealand Deformation Models

Another new method in GeoCalc is a deformation model for New Zealand. Deformation models are particularly interesting because they acknowledge that the world is moving. As Dave Doyle, a retired Chief Geodetic Surveyor for the United States says, “Everything is in motion, all the time!” Modern coordinate systems are beginning to acknowledge the motion of the Earth’s crust with the development of velocity models that map how the tectonic plates slowly drift around the surface of the planet. However, this slow, steady motion is not necessarily uniform. The plates and surface sometimes warp, twist, crunch together, pull apart, and generally change shape. Localized motion is a complicated factor in dynamic coordinate systems, and that’s where deformation models come in. 

These models are time-based by nature and are used to calculate where things were based on the distortions of the entire control networks. Deformation models help us to figure out where things are when a sudden shift in locations occurs, such as before and after an earthquake, but they also apply to slower motions that change the shape of a plate over time. The New Zealand deformation model is one such example. It factors in changes to the New Zealand landmass in snapshots of time, helping to calculate positions at the various points in time around seismic events. This allows specific models to be chosen to reflect a period of time where data may be applied from a particular epoch, similar to how a conventional time-based transformation helps more precisely model the changing earth. 

Zealand Deformation Model open in Geographic calculator
Information from a horizontal datum transformation shows the use of a newly added New Zealand Deformation Model.

Behind the Scenes US State Plane 2022

As most US-based GIS and geodesy experts are likely aware, new State Plane Coordinate Systems are in development. These state-based projected coordinate systems are used for official surveying purposes and for reporting survey data to state and federal survey authorities. Recently, the National Geodetic Survey (NGS) released provisional definitions for the coming updates to the State Plane zones. This is no small project; there will be 967 new coordinate systems as a part of this overall scheme of systems, adding in smaller area Low Distortion Projections, as well as larger single statewide projections, and some special use areas. This is a far greater number of systems than in the previous iteration of the State Plane system.

Additionally, as is common in Low Distortion Projections, the use of the Oblique Mercator projection has greatly increased. This is notable in the previous system where only one Oblique Mercator was used in Alaska. In the coming State Plane zones there will be many of them, and this is a potential area for trouble for folks not used to interpreting Oblique Mercator projections. There are parameters in this type of projection that can be interpreted in different ways, which over the years have only sometimes been easily compatible with various software package implementations built on different mathematical assumptions. 

While the preliminary zone definitions will not be used for another year or two until they become officially standardized by the NGS, and they may still change, Blue Marble is eager to bring them into GeoCalc and test them for compatibility and accuracy. We imported all 967 new zones and tested against the controls published by NGS, and we were happy to find that the results exactly match the control as expected. While we will not include these preliminary systems for a while yet, we are ready to implement the coming standards as soon as they are official. 

To learn more about the GeoCalc SDK and request a demo, visit

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