This page describes only the use and application of Coordinate Reference Systems in Orbit.
For a clear and short overview of the concepts of coordinate systems, datum and projections, read Coordinate Reference System in Theory.

CRS / SRS

A coordinate reference system (CRS) or spatial reference system (SRS) is a coordinate-based local, regional or global system used to locate geographical entities referring to a horizontal or vertical reference frame.. A coordinate reference system defines inter alia the representative volume of the earth, in case of projected systems the map projection method and the transformation between different spatial reference systems.
Coordinate reference systems can be referred to using a SRID integer, including EPSG codes defined by the International Association of Oil and Gas Producers.

Up to now Orbit supports any combination Geographic, Geocentric and Projected.

Orbit has the objective to support the most recent definition of all coordinate systems as defined by the OGP (International Association of Oil and Gas Producers) and described in the EPSG library. Orbit respects the order of axes as defined by the EPSG Library

Supported projection methods :

• Hotine_Oblique_Mercator (EPSG 9812)
• Krovak (EPSG 9819)
• Lambert_Conformal_Conic_1SP (EPSG 9801)
• Lambert_Conformal_Conic_2SP (EPSG 9802)
• Lambert_Conformal_Conic_2SP_Belgium (EPSG 9803)
• Mercator_1SP (EPSG 9804)
• Oblique_Mercator (EPSG 9815)
• Oblique_Stereographic (EPSG 9809)
• Transverse_Mercator (EPSG 9807)

Orbit supports any additional, local or custom projection in addition to the most recent projection as defined in the EPSG library.
A custom projection can be added via a .prj file structured as described by the Open GeoSpatial Consortium, see Projection Definition File.

How to add a custom CRS definition

1. Create your custom .prj file as described by the OGC, see above.
2. Rename prj file to be structured as “<number>_<description>.prj”, for example “1031370_Belge 1972 - Belgian Lambert 72.prj”
   • the number should be larger than 1,000,000 and smaller than 2,000,000 to avoid overlap with existing EPSG codes or dynamic Orbit coordinate systems.
   • the description is optional
3. Copy file to <Orbit installation directory>\program\system\crs
4. Restart Orbit.
   The newly added CRS will be available via the CRS Window by entering its name as defined in the .prj file, its number as defined in the file name or via “Undefined Area” (CRS By Country).

Orbit adds on demand local coordinate systems and grid corrections as defined by the local authorities :

• Belgium : Belge 1972 / Belgian Lambert 72 and Ostend height
• Great Britain and Republic of Ireland : OSGB 1936 / British National Grid and Local ortho height, OSNI 1952 / Irish National Grid, TM75 / Irish Grid
• Israel : GCS Israel / Israel TM Grid
• The Netherlands : Amersfoort RD New / NAP

Contact the Orbit support team to embed your local defined coordinate system.

The powerful Orbit engine can be used to add any geoid model or dem via an Orbit raster file (.omi) or via a mathematical description.

To support your local geoid model in Orbit you can provide your geoid (raster) definition and specifications to the Orbit support team.
This can be as text/csv file (containing X,Y,Z) or any supported raster resource.
The Orbit team will process the required configuration files which can be added on the fly like a custom CRS definition.

Every single resource has a CRS.
If no Orbit dataset CRS is set, Orbit will read the resource assuming that dataset has the same coordinate system as the MapCanvas (see below). When combining resources with different coordinate system it is strongly recommended to define the coordinate system for every single resource.
Orbit supports imagery to be reprojected on the fly.

There are two ways to set the CRS of a dataset in Orbit :

• Dataset Context Menu > Dataset General Properties
• Dataset Context Menu > Coordinate Reference System > Define Dataset CRS

The dataset CRS is saved in the Orbit Resource Descriptor file :

• Orbit Resource Descriptor

All resources are displayed in the map coordinate reference system. If a dataset crs differs from the map crs than the dataset will be re-projected on the fly to be displayed.

Optimize performance
Re-projecting datasets from their source crs into another target map crs requires processing time. Consequently large vector or point cloud resource will take more time to load and will slow down map rendering. It is advised to avoid on the fly re-projection by using the dataset source crs as map crs. When using multiple resource having different crs, the largest dataset crs combination should be used as map crs.

Deformations
Re-projecting means deforming. To retain shape, angles and presentation it's again advised to used the dataset crs as map crs.

Define Map CRS
The Map CRS can be changed quickly via the map status bar “Coordinate Reference System selection” window.
Open this window via a single click on the current map crs in the map statusbar.

The map crs on start-up is defined in your workspace

• Orbit desktop Standalone : Orbit GIS Workspace file
• Orbit desktop Client, set by administrator in Workspaces

Default behavior and preferences
If no datasets are visible in the current workspace, than the first visible datset crs will be used as map crs.