  Sky imaging systems use lenses to acquire images concentrating light beams in
a sensor. The light beams received by the sky imager have an elevation angle
with respect to the device normal. Thus, the pixels in the image contain
information from different areas of the sky within the imaging system field of
view. The area of the field of view contained in the pixels increases as the
elevation angle of the incident light beams decreases. When the sky imager is
mounted on a solar tracker, the light beam's angle of incidence in a pixel
varies over time. This investigation formulates and compares two geospatial
reprojections that transform the original euclidean frame of the imager plane
to the geospatial atmosphere cross-section where the sky imager field of view
intersects the cloud layer. One assumes that an object (i.e., cloud) moving in
the troposphere is sufficiently far so the Earth's surface is approximated
\emph{flat}. The other transformation takes into account the curvature of the
Earth in the portion of the atmosphere (i.e., voxel) that is recorded. The
results show that the differences between the dimensions calculated by both
geospatial transformations are in the order of magnitude of kilometers when the
Sun's elevation angle is below $30^\circ$.
