Using Lunar Reconnaissance Orbitor LOLA data to create accurate Lunar terrain scenes
As part of a multi-year NASA grant, Home Run Pictures will be producing a 20 minute fulldome format show in partnership with the Baton Rouge, LA and Houston, TX planetariums. The storylines are based on future mission concepts NASA has in its current long-term plans. One sequence in production involves the visualization of a future Lunar base located at the south pole of the Moon... a current "best" location chosen because of the confirmation of frozen water in the Shackelton Crater and the constant availability of the Sun to generate power. Home Run Pictures had previously produced a similar sequence five+ years ago, but at that time, we discovered that there was very little accurate elevation data on the Moon's surface... limited to the very old and very low resolution Clementine data. So, back then, we had little choice but to "fake" the terrain as best we could from available Apollo imagery.
But after having excellent results producing planet Mars terrain for Pittsburgh's Buhl planetarium using MOLA data acquired by NASA orbiting satellites... we we hoping that NASA's new Lunar Reconnaissance Orbitor had acquired data (LOLA) that would allow us to create more realistic Lunar terrain for our new show. What follows is a short case history of how we managed to take the LOLA data in its raw form and create fulldome scenes using our studio's Maya-based software toolset.
The LOLA data is readily accessable online. but in a raw format. For our Mars show we had passed the MOLA raw data through some indirect import conversions into the Terragen software application to generate detailed polygon meshes of the various locations we needed. These meshes were then exported in to the Maya software application for use. Although we were able to create some very nice background terrains, the meshes needed to contain massive amounts of polygons and were difficult to work with interactively and rendered slowly. So after some R&D, we adopted a different approach this time because of some updated tools now available in our production pipeline.
The raw LOLA data is basically arrays of numbers representing the elevation of the Lunar surface across a defined section of the Moon's sphere. Since we were creating our Lunar base at the proposed south pole region, we started with the data for latitudes -80 to -90. Using the NASA ISIS toolset, a grayscale raw Photoshop image was generated and then converted to a 16bit tif image for use in Maya. This file contained all the elevation values as grayscale levels, the lowest altitudes being black and higher altitudes gray to white as appropriate. Using a 16bit tif file contained a wider value range from black to white, around 32,000+ levels, instead of the usual 256 levels in the typical 8bit file. This would allow for much more detail in our terrain.
The usual pipeline path would be to then generate a mesh model from the tif file values for use, but after our experience with the Mars meshes, we looked for an alternative approach. We still did create some meshes for close-in scenes as appropriate, but we discovered another path worked better for larger expanses of terrain. When using the Mental Ray renderer with Maya, the creation of the mesh (displacement from a simple flat primative plane) only occurs during the final render so there is no need to work with a mesh interactively. Positioning during the animation and staging process can be handled with Maya's IPR interactive fast render tool.
The final rendered surface ends up being more detailed, more accurate as well as much faster to render. The number of polygons used by the renderer is varied depending on the detail needed in specific areas and you have many control value settings over how the renderer samples the tif data file to determine the elevations and create a detailed yet smooth surface. Today's 64bit operating system environoment allow for unlimited memory usage by applications so you can truely push the whole rendering process.
The detail you end up with is absolutely exciting to see... and the fact that it is actual data makes it an even more appropriate planetarium scientific visualization. By clicking the various images shown here, they will link to a larger image, so you can see them at a larger resolution to better appreciate the detail in the terrain. There still is a limit as to how close you can get before the resolution of the data becomes insufficient, and in those cases we had to resort to the old "fake it" routine and add some texturing to the displacement mesh via bump/normal texture mapping.
There is some artifacting present in the LOLA data because of the orbiter's scanning process that needs to be processed out. As time goes on the Lunar Reconnaissance Orbitor will continue to scan the Moon's surface, so the LOLA data will improve in quality and the available resolution will increase. The scenes shown here are of a futuristic shuttle as it approaches the south pole Lunar base, finally passing over the Shackelton Crater where the permanent human settlement will be perched on the crater's rim.
© 2011 H o m e R u n P i c t u r e s