\section{Conclusions and Future Work}

Using a spherical approach to PGM, we have presented a planetary terrain renderer that accurately handles differently projected data.
Additionally, we have shown how reducing the ray-sphere intersection to a two-dimensional cross section can greatly optimize the ray casting process.

To improve our algorithm, we suggest sorting the datasets into a spatial hierarchy therefore allowing for visibility tests to be performed by the CPU, possibly eliminating entire composition passes.
Additionally, finding the radius of the primary reference sphere through min mipmapping is effective but slow due to the reduction performed on the GPU.
To improve this, we suggest the use of CUDA~\cite{CUDA} which allow for easier management of the shader cores.
Lastly, we would like to provide a method for streaming data from the disk to RAM to GPU memory so that high-resolution data can be rendered.


