By Peter Joynt
It is not often in geology that mineralisation or geological units behave in a consistent planar fashion. The earlier article on interpolation and anisotropy by Kirk Spragg outlined a detailed explanation of Leapfrog’s global trend and how it affects the interpolation of points. This article aims to give users an introduction to the application of structural trends and how they can be applied to a model to handle different situations.
What is a Structural Trend?
A structural trend is a generalisation of the global trend that allows changes in direction of continuity over a defined surface. Instead of being based on a plane like the global trend with the user defining the ellipsoid ratios, the structural trend is based on a surface. This surface can be any shape or orientation usually defined by geological constraints such as faulting, foliation etc. The surface is then effectively down sampled to determine the local trend at each point on the mesh to give the user an anisotropy that varies throughout the defined space. This makes the structural trend perfect for geological units or mineralisation that is not planar. The structural trend does not determine the final surface; this is still done by the interpolant and the data points used. In Leapfrog the default interpolant type is isotropic, which lets us more easily visualise trends that are often hard to pick up when looking at raw data. Figures 1, 2 and 3 show the difference between an isotropic interpolant, global trend and a structural trend.