  This paper describes a framework for capturing geological structures in a 3D
block model and improving its spatial fidelity given new mesh surfaces. Using
surfaces that represent geological boundaries, the objectives are to identify
areas where refinement is needed, increase spatial resolution to minimize
surface approximation error, reduce redundancy to increase the compactness of
the model and identify the geological domain on a block-by-block basis. These
objectives are fulfilled by four system components which perform block-surface
overlap detection, spatial structure decomposition, sub-blocks consolidation
and block tagging, respectively. The main contributions are a coordinate-ascent
merging algorithm and a flexible architecture for updating the spatial
structure of a block model when given multiple surfaces, which emphasizes the
ability to selectively retain or modify previously assigned block labels. The
techniques employed include block-surface intersection analysis based on the
separable axis theorem and ray-tracing for establishing the location of blocks
relative to surfaces. To demonstrate the robustness and applicability of the
proposed block merging strategy in a more narrow setting, it is used to reduce
block fragmentation in an existing model where surfaces are not given and the
minimum block size is fixed. To obtain further insight, a systematic comparison
with octree subblocking subsequently illustrates the inherent constraints of
dyadic hierarchical decomposition and the importance of inter-scale merging.
The results show the proposed method produces merged blocks with less extreme
aspect ratios and is highly amenable to parallel processing. The overall
framework is applicable to orebody modelling given geological boundaries, and
3D segmentation more generally, where there is a need to delineate spatial
regions using mesh surfaces within a block model.
