Website Updates

Suggestions for website improvements may be made by emailing Tenielle Gaither.

Control Networks

A control network is made up of a network of control points. A control point is a location on a planet or satellite that is used as a reference. A grouping of control points in a control network allow us to accurately calculate the location of a feature on a planet or satellite in relation to the network of control points that are contained in the control network.

There can be numerous control networks for a planetary body because as more accurate data are obtained, the location of the control points change, and all of the features that have their locations defined in relation to a particular control network must be updated to reflect their new location in relation to the new data.

Coordinate Systems

For each planetary body the IAU has designated one or more coordinate systems. You can view a list of these accepted coordinate systems here. This website supports conversions between coordinate systems to allow for retrieval of the data in the system most useful to the user.

Planetographic and Planetocentric Latitudes

All planetary bodies currently in the nomenclature database, except for Mars, are defined as a sphere even if the body is not very spherical. For the triaxial bodies, the IAU defines a best-fit sphere to approximate the shape for cartographic applications. One benefit for using a sphere is that a planetocentric and planetographic defined latitude will be the same. However, for Mars, which is defined as an ellipse (biaxial), the two latitude systems are indeed different.

A planetocentric latitude is defined as the angle between the equatorial plane and a line from the center of the body. The planetographic latitude is the angle between the equatorial plane and a line that is normal to the body. Both latitudes are equivalent on a spherical model, but they can differ by quite a bit on an ellipsoid. For further reading, see the section of the Isis Workshop page called Latitude Type.

Downloading Data

CSV - Comma Separated Values

The CSV format can be opened by most spreadsheet programs (eg: excel). Diacritic characters are encoded in UTF-8, you may need to manually set the character encoding in your spreadsheet program to get them to display correctly.

TSV - Tab Separated Values

Very similar to the CSV format, only using the tab character to separate the columns. Diacritic characters are encoded in UTF-8, you may need to manually set the character encoding in your spreadsheet program to get them to display correctly.

XML - Extensible Markup Language

The XML format is best for programatically interacting with the data. One of the easier ways to process xml documents is with an XSLT which will transform an xml document into nearly any other text based format.

KML - Keyhole Markup Language

The KML format is an OGC standard mainly used by Google Earth for graphically displaying geospatial information on a map. The latitudes and longitudes for this format are only in the -180 to 180, positive east, planetocentric coordinate system.

Shapefile

The Shapefile format, developed and regulated by ESRI, is a popular vector-based geospatial format for GIS software. A shapefile is used to spatially describe various vector geometries including points, polylines (lines), and polygons. Each feature also contains a table entry to store the nomenclature attributes. Due to field width restrictions in this format, field names for the nomenclature database have been shortened. For more information, please see http://en.wikipedia.org/wiki/Shapefile