Here are the data structures with brief descriptions:
| htm_ids | A sorted list of 64 bit integer ranges |
| htm_range | Represents a range of integers |
| htm_s2cpoly | A convex polygon on the sphere |
| htm_s2ellipse | An ellipse on the sphere, defined as the points p such that angsep(p, f1) + angsep(p, f2) <= 2a, where a is the semi-major axis angle of the ellipse and f1/f2 are its focii |
| htm_sc | Spherical coordinates (in degrees) for a point in S2 |
| htm_tree | An HTM tree containing a list of points sorted on HTM ID (tree entries), and optionally an index over the points that allows for fast spatial searches/counts |
| htm_tree_entry | An entry (a row ID and a position) in an HTM tree |
| htm_tri | A structure describing the geometry of an HTM triangle (aka a trixel) |
| htm_v3 | Cartesian coordinates for a point in R3 |
| htm_v3p | A position and a payload |
