We're Not Flat-Earthers. We Promise.
The engineers at Kongsberg Geospatial know the world isn’t flat, but it’s not a simple spheroid, either. The 3D globe is neither smooth, nor spherical, and many 3D projections fail to accurately represent this.
As a starting point, our TerraLens SDK uses the EGM96 geoid model, which adds the expected “bumpiness” to the flat globe. Developers can also switch to the updated WGS84 ellipsoid model, but this will assume base terrain elevation of 0.
To help address this, TerraLens allows the integration of multiple elevation sources, including DTED, elevation GeoTIFF data and SRTM. The engine will allow multiple sources and resolutions and data sources to be combined in a single terrain model – over which 2D representations and maps can be draped.
The altitude reported by an airborne sensor for different data sets may mean relative to ground or relative to sea level. TerraLens supports both concepts, with an API allowing each geographic presentation to indicate how its altitude value should be interpreted.
There is a significant amount of terrain elevation data available for either geoid model for virtually any geographic location on the globe, but it can vary in terms of resolution, cost, and availability depending on the location. TerraLens’ capability to merge multiple terrain sources into a single mesh allows application developers to dynamically combine or swap sources depending on the level of detail they need.
The fact that the earth isn’t flat can impact 2D map applications as well. In order to create 2D maps, 3-dimensional terrain has to be projected onto a 2D plane, and the type of projection that’s employed can significantly alter how the terrain appears onscreen.
By default, the default projection for map applications is either Mercator or Web Mercator. This is a good compromise projection that works well enough for a wide range of applications in latitudes where most major cities are located, but it can produce increasing distortion in areas closer to the poles, and it is of no use at all for applications like maritime navigation, (where you require conformal relative angles), or for viewing aeronautical charts (where you are navigating in great circle arcs).
The TerraLens visualization SDK ensures geographically defined maps and overlays are properly geo-rectified for their intended application by accounting for the projection used in the data source – as well as the potentially different projection used to render them in the application window.
TerraLens supports dozens of projection and spheroid models, so you can visualize geographic data where and how you need it. This includes mapping high latitudes (where you might use PolarStereographic or AlaskaConformal projections); navigation (where might want to use conformal projections like Mercator or UTM); and viewing aeronautical charts (where you would use azimuthal projections, including Orthographic projection).
The center of projection can be dynamically re-adjusted as the viewed area changes, helping to minimize projection artifacts. This can be critical for applications that cover large areas, or require a high degree of accuracy. A complete list of supported spheroid models and projections is available on the TerraLens product specifications page.