Vesta Images – Vesta global image (RC3)

Mosaics of Vesta images obtained during the third rotation characterization (RC3) observation by Dawn. The images used were obtained on July 24, 2011 from a distance of about 5200 km. Each mosaic is created from four sets of source images that have been draped over a shape model of Vesta. The terminator was then corrected. Due to Vesta's fast rotation there is no simple or easy way to assemble global mosaics where the terminator area is accurate. This is the reason I draped the images over a shape model of Vesta. Vesta's fast rotation means that areas on the edge of the sunlit portion of Vesta rotate quickly into darkness, making noticeable changes in the length and positions of shadows in the time that separates one image from another.

I used the shape model and viewing geometry information to create simple cylindrical maps from the images. I then then used the shape model to render the maps without applying shading (the maps were draped over the model). I then rendered them again, this time with shading. The next step was to take the terrain near the terminator in the shaded renders and paste it into the non-shaded image using a feathered selection in Photoshop. Of course the shaded image data was too dark so I brightened it until there was no visual difference along the selection edges. This resulted in a realistic-looking image, even though some discrepancies in the direction of shadows might be visible somewhere if you look closely.