Earth  ID: 4308

SIGGRAPH Daily 2015: How did we tile Greenland?

In NASA’s Scientific Visualization Studio we work with many Earth science datasets in different geographic projections that must be accurately positioned on the globe. Defining and mapping these by hand with individual manifold shaders is time-consuming and error prone. We developed an Interactive Data Language routine that automatically extracts the coordinate and projection information from geotif images. For each image, this routine writes out a Renderman Shading Language #include file passing the correct parameters to a projection routine that positions the related texture tile. The projection routine is a C++ Renderman plugin that computes the projection calculations in double precision. String formatted parameters to the projection plugin also allow double precision. We then create a “map-multiple” #include file referencing all the individual #include files in a tile set. This “map-multiple" file is added to an SLbox in SLIM so that the compiled shader references the appropriate tiles.

We employed this method with high-resolution data for Greenland. From the Greenland Ice Mapping Project at Ohio State we obtained 30-meter topography data along with an ocean and an ice sheet mask. Each of these datasets consisted of a 6 x 6 array of 124 megapixel tiles. We also received seven sets of 20-meter Radarsat data from the Canadian Space Agency, mosaicked at the University of Washington‘s Applied Physics Lab. Each set consisted of a 5 x 5 array of 421 megapixel tiles.

Using these tools, we generated 294 #include files to map this data: 108 for the topography data, the ocean and the ice sheet masks, 175 for the Radarsat brightness files and 10 for the “map-mulitple" files. The final master #include file includes all of the “map-multiple” files. With this method, we accurately mapped over 87 gigapixels of Greenland data.

Visualization Credits

Cindy Starr (GST): Lead Visualizer
Greg Shirah (NASA/GSFC): Visualizer
Ian Howat (Ohio State University): Scientist
Ian Joughin (Polar Science Center, University of Washington): Scientist
Twila Moon (National Snow & Ice Data Center, CIRES, University of Colorado, Boulder): Scientist
Please give credit for this item to:
NASA's Scientific Visualization Studio

Radarsat data courtesy of the Canadian Space Agency, mosaicked by Ian Joughin, Applied Physics Laboratory, University of Washington

GIMP Topography courtesy of the BPRC Glacier Dynamics Research Group, Ohio State University

The Blue Marble data is courtesy of Reto Stockli (NASA/GSFC).

Additional credit goes to Canadian Space Agency, RADARSAT International Inc.

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Data Used:
Greenland Mapping Project (GIMP) Digital Elevation Model 2003 - 2009
RADARSAT-1/SAR 2000 - 2013
Note: While we identify the data sets used in these visualizations, we do not store any further details nor the data sets themselves on our site.

This item is part of these series:
Narrated Movies

GCMD >> Earth Science >> Cryosphere >> Glaciers/Ice Sheets >> Ice Sheets
GCMD >> Earth Science >> Hydrosphere >> Glaciers/Ice Sheets >> Ice Sheets
NASA Science >> Earth
GCMD >> Earth Science >> Terrestrial Hydrosphere >> Glaciers/Ice Sheets >> Ice Sheets

GCMD keywords can be found on the Internet with the following citation: Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version