Description of the Ceres SPC Shape and Regional Models bundle V1.0 ================================================================== Bundle Generation Date: 2024-07-09 Peer Review: 2024_Asteroid_Review Discipline node: Small Bodies Node Content description for the Ceres SPC Shape and Regional Models bundle ====================================================================== This bundle contains 9 regional Digital Terrain Models (DTMs) of craters with Permanently Shadowed Regions (PSRs) of the asteroid Ceres. 7 of these DTMs are located near the north pole, while 2 are located near the south pole. These DTMs were generated using secondary illumination (i.e. light reflected off crater walls), enabling height determinations within the PSR. We also provide a shape model, or global DTM, to provide context for the regional DTMs. The shape model is of good quality, though it should be stressed that the global model was generated as a stepping stone to generate the regional models, and may not have the “polish” of typical SPC shape models. All products were generated by Robert Gaskell using the Stereophotoclinometry (SPC) software suite, with the addition of new tools to utilize secondary illumination. The models were constructed using the Dawn Framing Camera images. All image filters were used to generate topography, though ~75% had a broadband (clear) filter. Most images were from Framing Camera 2, though ~2% of the images were from Framing Camera 1. Non-calibrated images are used, but we apply a correction for geometric distortion. The regional topography data is provided both in cubes readable by the USGS ISIS program, and as a geoTiff which can be read by programs such as ArcGIS. To aid the data user, filenames end with a “c” to designate ISIS cubes or a “g” to designate geoTiffs. Internal checks allow us to estimate the uncertainty of the model, but this value should not be treated as a rigorous solution, rather as a soft solution. A good rule of thumb for the regional uncertainty is to base it off the regional model ground sample distance (GSD). This means the 100 m GSD regional models will have an uncertainty of 100-200 m, while the 40 m GSD regional models will have an uncertainty of 40-60 m. The shape model is provided in a variety of formats. To aid the data user, filenames end with a letter to designate the format. These letters are “i”, “c”, “g”, “p”, and “o”, respectively. "i" - ICQ - Implicitly Connected Quadrilateral format, one of the smallest data size formats. It is defined in icqmodel.asc of Gaskell (2020). "c" - ISIS - The native cube format for the United States Geological Survey (USGS) Integrated Software for Imagers and Spectrometers. "g" - GeoTiff format, an expanded version of TIFF images that maintains physical geometric information, which is especially useful by GIS programs like ArcGIS. “p" - Plate vector format, an older format used by the Planetary Science community. "o" - OBJ, a plate vector format, and an Object Vector format, created by Alias Wavefront but is currently one of the most common formats for 3D models. This format is the native format for the Small Body Mapping Tool (SBMT). We also provide quality assessment data for the shape model to include the best image resolution, number of images, best maplet resolution, and the sigma value. The quality data is presented in 1 degree bins using the USGS ISIS cube format. The assessment data show that the radius is everywhere good, and regional models could be generated almost anywhere on Ceres to improve on the resolution of the global model. Details about the products are given in document/productdescription.txt, while the assessment and thumbnails of the assessment data are given in document/ceresshapeassessment.pdf. The shape assessment PDF is particularly important. The shape model is provided in two resolution versions for the ICQ, PLT, and OBJ. One version has a higher resolution of 1.3 km Ground Sample Distance (GSD), and the other has a lower resolution with a 5.3 km GSD since many software programs cannot read the higher resolution version. The cubes and geoTiffs of the global model have a single version, that of a GSD of 1.3 km. Since the maplets that make up the shape model everywhere have a higher resolution than the global model, a good rule of thumb for the global uncertainty is to base it off the shape model GSD. The uncertainty is then one to two times the shape GSD. This means that the higher resolution model, with a 1.3 km GSD, will have a minimum uncertainty of 1.3 to 2.6 km. The lower resolution model, with a 5.3 km GSD, will have an uncertainty of 5.3 to 10.6 km GSD. The files are organized into four subdirectories. Global data files are in data/global/, North Pole regional data files are in data/regionalnp/, South Pole regional data files are in data/regionalsp/, and document files are in document/. Caveats to the data user ======================== The regional geoTiff files are projected and resampled data. This process requires smoothing of the source data from the regional cubes. The global geoTiff files contain the same information as the global cubes, though both are resampled data from the ICQ data.