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What are product footprints and how do I use them?
Many geosciences-related products have a surface location. This surface location can be described with a "footprint", i.e. the area of the surface that is covered by the product. The specifics of the footprint, i.e. how the product "covers" the surface, will vary depending on the product type. Image products have a coverage area, i.e. the area covered by the image. But products like the SHARAD instrument have a coverage better described as a line across the surface. Other products like the MOLA PEDR records are individual measurements at a given lat/lon, which are best described by points.
ODE uses product coverage footprints aid in finding products by using locations and helping the user determine if the product meets their needs. To support cross-mission/instrument searching and visualization, ODE generates footprints in common coordinate systems with common attributes such as how the footprint center is determined. Footprints are generated in a variety of methods: in some cases, the footprint is directly taken from the label (footprint or reticule points or lat/lon bounding boxes); from the appropriate PDS Archive index file; directly from the product or related products (example: CRISM TRDR from the DDR data file); or from USGS’s Unified Planetary Coordinate database. The specific method used for a given product can be found in the ODE notes at the bottom of the product result page’s metadata tab page.
A few highlights about footprints:
  • Common coordinate system
    • Planetocentric
    • Positive East Longitudes (stored in 0-360 degrees but sometimes shown in -180..180 degrees depending on the projection)
  • Common center calculation
    • For lines this approximately halfway along the line from start to finish
    • For areas, the center is usually calculated as the intercept between two great circle routes – one from the max lat/west longitude corner to the min lat/east longitude corner and one from the min lat/east longitude corner to the max lat/west longitude corner. This approach generally works well for footprints that range from simple rectangles to long image strips typical of many imaging instruments. However, it can break down at the poles and place the center along the edge of the footprint or even, in some cases, outside the footprint.
  • Points/vertices are rounded to three decimal places
  • A single product may have multiple individual footprints depending on the nature of the instrument and the noise in the data
  • Complex area footprints that cross over themselves have been broken into multiple simple footprints that do not cross over themselves (typically due to noisy data)
Footprint Type Attributes
Area
  • Footprint Outline
  • Lat/Lon Bounding Box
  • Center Point - location at approximately the center of the polygon
Line
  • Footprint Surface Line
  • Lat/Lon Bounding Box
  • Center Point - located along the surface line halfway from the start to the end
Center Point Point
ODE currently offers three ways to use footprint data:
  • through ODE's own web map interface (Note: An updated web map interface will be released with ODE V3.0)
  • via the Google Earth/Mar globe tool
  • within GIS tools that read ESRI's Shapefile format including ESRI's ArcGIS tools
Footprint data is often used in a variety of map projections:
  • cylindrical projections with a center longitude of zero (longitude range of -180 to 180)
  • cylindrical projections with a center longitude of 180 (longitude range of 0 to 360)
  • globes (ala Google Earth/Mars)
  • polar stereographic projections
To meet the various interface and projection needs, ODE generates a wide range of footprint coverage data in a variety of formats. ODE itself uses cylindrical center longitude zero projected footprints in its own map display. ODE also generates:
  • Individual footprints in KML global projections for Google Earth/Mars
  • Individual footprints in ESRI Shapefile format for Shapefile enabled GIS tools
    • Cylindrical Center Longitude Zero Projection
    • Cylindrical Center Longitude 180 Projection
    • Global Projection (suitable for Polar Stereographic Projections)
  • Product type coverage maps in KMZ global projections for Google Earth/Mars
  • Product type coverage maps in ESRI Shapefile format for Shapefile enabled GIS tools
    • Cylindrical Center Longitude Zero Projection
    • Cylindrical Center Longitude 180 Projection
    • Global Projection (suitable for Polar Stereographic Projections)
    • Global North Projection
    • Global South Projection
    • Associated Centers in Global Projection
see tables below for more details
The cylindrical projected footprints are modified to handle edge crossings (by splitting footprints that cross the left and right edge) and pole conditions (by adding vertices at the poles).
Individual Product Derived Footprint File Types
Individual Product KML/ KMZ Global Footprint File Holds an individual footprint. All longitudes are in the form -179.999 to 180. The footprints also include a center point. Can be found under the Derived File tab of the product's results page (assuming the product has location data).
Individual Product Global Shapefile Zip or Tar.Gz File Holds an individual footprint suitable for polar projections. All longitudes are in the range 0..360. Can be found under the Derived File tab of the product's results page page (assuming the product has location data).
Individual Product Cylindrical 0..360 (Center longitude 180) Shapefile Zip or Tar.Gz File Holds an individual footprint suitable for cylindrical projections with a center longitude of 180. All longitude are in the range 0..360. Can be found under the Derived File tab of the product's results page page (assuming the product has location data).
Individual Product Cylindrical -180..180 (Center longitude 0) Shapefile Zip or Tar.Gz File Holds an individual footprint suitable for cylindrical projections with a center longitude of 0. All longitude are in the range -180..180. Can be found under the Derived File tab of the product's results page page (assuming the product has location data).
Shapefiles are actually made up of five individual files: .SHP, .SHX, .PRJ, .SHP.XML, and .DBF. To aid in downloading the entire shapefile, the individual shapefile files are provided together in a zip or tar.gz compressed file.
Footprint Coverage Maps (KMZ, ShapeFiles)
Please see What are Footprint Product Coverage Maps and How Do I Use Them?

What is ODE's relationship to Google Earth and what are KML/KMZ files?
Google Earth offers a convenient way to view footprint data from ODE. ODE uses Google Earth for viewing individual footprints and product type coverage maps. KML/KMZ files are the standard Google Earth file formats. You can download these files or have your browse configured to open Google Earth when accessing these file types.
Using Google Earth for Mars Products
  1. Download Google Earth from http://earth.google.com/ (you will need Google Earth 5.0+ to use the Mars view)
  2. Open Google Earth
  3. Switch to Google Mars - Use the small planet icon at the top of the map:

    This Mars model helps users to fly anywhere on Mars to view satellite imagery, maps, and terrain such as Mars Digital Image Map (MDIM 2.1), Thermal Emission Imaging System (THEMIS) mosaics, Mars Orbiter Laser Altimeter (MOLA) data. Users can explore rich geographical content through High Resolution Stereo Camera (HRSC), Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), High Resolution Imaging Science Experiment (HiRISE), Context Camera (CTX), and Mars Orbiter Camera (MOC) data.
  4. Now any KML/KMZ file opened will overlay the mars map:
Using Google Earth for Lunar Products
  1. Download Google Earth from http://earth.google.com/ (you will need Google Earth 5.0+ to use the Moon view)
  2. Open Google Earth
  3. Switch to Google Moon - Use the small planet icon at the top of the map:
     
    This Moon model helps users to take tours anywhere on Moon to view visible imagery taken by the Clementine Mission, geologic and topographic maps, and placemarks detailing the Apollo missions. Users can also view 3D models of landed spacecraft, zoom into 360-degree photos to see astronauts' footprints, and watch rare TV footage of the Apollo missions.
  4. Now, you can overlay Lunar KML/KMZ files just like for Mars. 
Using Google Earth for Mercury Products - Using Google Earth for Mercury products is not quite as convenient but it can be done. Please follow the steps shown below.
  1. Download the following KML file and png image to your local machine, and save them in the same folder.
  2. If you have already installed Google Earth on your machine, just skip this step to install Google Earth.
  3. Start Google Earth. Since Google Earth does not include a Mercury model now, you can view the map either through a Mars model or with an Earth model. In the Earth model, go to the Layers sub panel, uncheck the layers in the Primary Database.
  4. Open the Mercury basemap by double clicking the file "Mercury_Basemap.KML" directly, or open through the file menu in Google Earth. You will find a Mercury shaded relief map produced by the USGS Flagstaff AZ. Scanned from published map USGS I-1149, 1979.
    • If you expand the plus sign besides the KML file,

      you will find more information of the data show as follows.

    • Double click the link "Download original Mercury map from USGS", the web will direct you to the USGS website shown at the bottom of the Google Earth page.
  5. Now, you can overlay Mercury KML/KMZ files just like for Mars.

What is ODE's relationship to Google Earth/Mars and individual product footprints?
Individual product footprints can be found under the Product Results Page's Derived Files tab. Derived files with a ".kml" extension can be view within Google Earth/Mars. Opening the file in Google Earth will display the footprint with a center point. Selecting the center point will open a pop-up display with links to PDS including a link directly to ODE's Product Result Page for that product.

Introduction of KML/KMZ
Keyhole Markup Language (KML) is an XML (eXtensible Markup Language)-based language schema for expressing geographic data and visualization on existing or future web-based, 2-D maps and 3-D Earth browsers including Google Earth (Google Inc. 2008), Google Maps, Google Maps for mobile, NASA WorldWind, ESRI ArcGIS Explorer, and Yahoo! Pipes. KML files can be created using Google Earth, Google Maps, or ESRI ArcGIS, or using a plain text editor to create the files from scratch. KMZ files are zipped KML files packaged with images. Information about KML/KMZ can be found in:

What is ODE's relationships ESRI's ArcGIS and what are Shapefiles
Footprints can be exported from ODE in ESRI's Shapefile format. Shapefile format (see section 4.15.1) store both the footprint location data as well as a table of product attributes including the instrument host, instrument, product type, dataset, product id, and a URL back to ODE's Product Result page for that product. Several GIS tools including ESRI's ArcGIS, can read Shapefiles.
Since Shapefiles actually consist of several individual files, ODE provides the files in either Zip or Tar.Gz form. Just download the Zip or Tar.Gz file, unzip, and open in your GIS tool.
Shapefiles, developed and regulated by ESRI, is a popular geospatial vector data format for GIS software. A shapefile is used to spatially describe geometries: points, polylines, and polygons. And it is commonly refers to a collection of mandatory files with ".shp", ".shx", ".dbf", and other optional extensions such as ".prj", ".sbn" and ".sbx" on a common prefix name (e.g., "mars_mex_pfs_edrnom_northcenters_a.*"). The content of the mandatory and optional files are listed as follows
Mandatory files:
  • * .shp - shape format; the feature geometry itself
  • * .shx - shape index format; a positional index of the feature geometry to allow seeking forwards and backwards quickly
  • * .dbf - attribute format; columnar attributes for each shape, in dBase III format
Optional files:
  • * .prj - projection format; the coordinate system and projection information, a plain text file describing the projection using well-known text format
  • * .sbn and * .sbx - a spatial index of the features
  • * ..fbn and .fbx - a spatial index of the features for shapefiles that are read-only
  • * .ain and .aih - an attribute index of the active fields in a table or a theme's attribute table
  • * .ixs - a geocoding index for read-write shapefiles
  • * .mxs - a geocoding index for read-write shapefiles (ODB format)
  • * .atx - an attribute index for the .dbf file in the form of shapefile.columnname.atx (ArcGIS 8 and later)
  • * .shp.xml - metadata in XML format
  • * .cpg - used to specify the code page (only for .dbf) for identifying the character encoding to be used
The actual shapefile relates specifically to files with the ".shp" extension, however this file alone is incomplete for distribution, as the other supporting files are required. All files should be located in the same folder. And the shape file can be read by ESRI ArcGIS and ENVI. More information about shape file can be found in the following reference.
Environmental Systems Research Institute, Inc. (July, 1998). "ESRI Shapefile technical description".

What are Footprint Product Coverage Maps and How Do I Use Them?
Product coverage maps include all footprints for a given instrument host, instrument, and product type (identical to ODE's Product Search page). These can be found under the Coverage Tool under the Tools tab. Opening the file in Google Earth will display the footprint with a center point for each footprint Selecting the center point will open a pop-up display with links to PDS including a link directly to ODE's Product Result Page for that product.
ODE generates these footprint coverage maps for each product type from each mission/instrument stored in ODE. For example, ODE Mars provides a map for all MRO HiRISE RDR footprints. The coverage maps show all the footprint coverages for the mission/instrument/product types. In addition, there are some special coverage maps such as the CRISM TRDR/DDR FRT/HRL/HRS center swath only maps found in the ODE Mars Footprint Coverage Explorer Tool.
There are several versions of each coverage map. KMZ versions can be used in Google Earth. Shapefiles can be use in ESRI's ArcGIS tools or other GIS tools that support shapefiles.
  • Google Earth KMZ Format
  • Global Projection ESRI ShapeFile
  • Cylindrical Projection Center Longitude 0 ESRI ShapeFile
  • Cylindrical Projection Center Longitude 180 ESRI ShapeFile
Product Type Derived Footprint File Types
Footprint Product Type Coverage KMZ Map Holds a product coverage map in KMZ form. A coverage map includes the footprints of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range -179.999 to 180. The footprints also include a center point. Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type Global Shapefile Zip or Tar.Gz File ("gx") Holds a product global projection map in Shapefile format. A coverage map includes the footprints of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range 0 to 360. Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type Global Centers Shapefile Zip or Tar.Gz File ("gxc") Holds a product centers global projection map in Shapefile format. A centers coverage map includes the footprint centers of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range -0 to 360. Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type North Polar Shapefile Zip or Tar.Gz File ("nx") Holds product global projection map of products in the North hemisphere in Shapefile format. This is suitable for use in a Polar Stereographic map. A coverage map includes the footprints of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range 0 to 360. Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type North Polar Centers Shapefile Zip or Tar.Gz File ("sxc") Holds a product centers for the North global projection map in Shapefile format.. A centers coverage map includes the footprint centers of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range 0 to 360. Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type South Polar Shapefile Zip or Tar.Gz File ("sx") Holds product global projection map of products in the South hemisphere in Shapefile format. This is suitable for use in a Polar Stereographic map. A coverage map includes the footprints of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range -0 to 360. Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type South Polar Centers Shapefile Zip or Tar.Gz File ("sxc") Holds a product centers for the South global projection map in Shapefile format. A centers coverage map includes the footprint centers of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range 0 to 360. Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type Cylindrical 0..360 (Center longitude 180) Shapefile Zip or Tar.Gz File ("c180x") Holds a product cylindrical projection (center longitude 180) map in Shapefile format. A coverage map includes the footprints of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range 0 to 360. Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type Cylindrical 0..360 Centers (Center longitude 180) Shapefile Zip or Tar.Gz File ("c180xc") Holds a product centers cylindrical projection (center longitude 180) map in Shapefile format. A centers coverage map includes the footprint centers of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range -0 to 360. Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type Cylindrical -180..180 (Center longitude 0) Shapefile Zip or Tar.Gz File ("c0x") Holds a product cylindrical projection (center longitude 0) map in Shapefile format. A coverage map includes the footprints of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range -180 to 180 . Can be found under the Footprint coverage tool under the Tools tab.
Footprint Product Type Cylindrical -180..180 Centers (Center longitude 0) Shapefile Zip or Tar.Gz File ("c0xc") Holds a product centers cylindrical projection (center longitude 0) map in Shapefile format. A centers coverage map includes the footprint centers of all products of a given instrument host, instrument, and product type (identical to ODE's product search page). All longitudes are in the range -180 to 180. Can be found under the Footprint coverage tool under the Tools tab.
A note about Product Coverage Naming Conventions: Product coverage KML and shapefiles follow the following naming conventions:
  • KMZ: Target_InstrumentHostId_InstrumentId_ProductType{_UpperLeftCorner}{_with_time }.kmz
  • Shapefiles: Target_InstrumentHostId_InstrumentId_ProductType{_UpperLeftCorner}_type.(dbf|shp|shx|prj|shp.xml|zip|tar.gz)
There are two types of KML coverage files: with or without a time stamp associated with each product. Time stamped products allow users to control what product footprints are displayed based on the observation time. KML files with timestamps end with "_with_time".
Shapefiles are actually made up of five individual files: .SHP, .SHX, .PRJ, .SHP.XML, and .DBF. To aid in downloading the entire shapefile, the individual shapefile files are provided together in a zip or tar.gz compressed file.
Because many of the coverage maps are quite large, in addition to the coverage file encompassing the entire planet, ODE provides a set of 45x45 degree coverage tiles. The tiles have their upper left corner in latitude/longitude included in their file names. These tiles are generated by selecting all products with their CENTERS inside the tile. NOTE: FOOTPRINTS THAT CROSS INTO A GIVEN TILE BUT WHOSE CENTERS ARE IN THE NEIGHBORING TILES ARE NOT INCLUDED IN THE GIVEN TILE. Users should load the neighboring tiles when working close to a tile edge or products with large footprints.
Each shapefile name ends with a type, a character set "_xx" to "_xxxxxx". The first 1 to 4 characters after the "_" indicate the projection (as shown in the table above "g", "n". "s", "c0", "c180"), the next character indicates the shapefile type ("a", "l", "p"), and, finally, the name may end with a "c" to indicate that the shapefile holds product centers.
Shapefiles may only hold points, lines, or areas. Footprint coverage files holding areas have a "_xa" at the end of the name (ex. mercury_messenger_mdis-nac_cdr_cylclon0_xa). Footprint coverage files holding lines (such as SHARAD RDR's) have an "_xl" at the end. Footprint coverage files holding points (such as some MESSENGER MDIS products) have an ending of "_xp". In a few cases such as MESSENGER MDIS products, some products have just center points and some have areas so there are both "_xp" and "_xa" shapefiles.
The product centers are stored in a separate point shapefiles with a name ending in "c". "*_xpc" files are basically the same as the actual point footprint shapefiles. There is a corresponding centers shapefile for the global, north, and south coverage shapefiles. There are not corresponding centers shapefiles for the cylindrical center longitude 0 and cylindrical center longitude 180 shapefiles as the centers for the global shapefiles will also work fine in the cylindrical projections.
In most cases, the footprint product coverage will have eight shapefiles:
  • *_g{a|l|p}
  • *_n{a|l|p}
  • *_s{a|l|p}
  • *_c0{a|l|p}
  • *_c180{a|l|p}
  • *_g{a|l|p|c
  • *_n{a|l|p}c
  • *_s{a|l|p}c
However, in a few cases (example the MESSENGER MDIS datasets), there are both area and point shapefiles. This is because some products have a complete area and some only have a center point.