Modify Mesh Parameters

Use the Mesh > Modify option to change the default mesh generated by VOXI.

Modify Mesh Parameters dialog options

Active Volume Cell Size (m)
	X, Y, Z	The active volume cell size(s) along each axis. If the Variable option has been chosen for horizontal cells, the onus is on you to determine the number and size of consecutive cells within the bounds of the AoI. The syntax for defining variable cells is: n1xc1 n2xc2 n3xc3 etc… Where n is the number of cells and c is the cell size. The variable cell size definition only affects the X & Y coordinates. The cell sizes along the Z coordinate remain the same for all methods.
	[Half]	Half the number or elements (double the resolution) along each major axis.
	[Double]	Double the number of elements (half the resolution) along each major axis.
	[Reset]	Restore the initial cell sizes.
Dimensions
	Active	This read-only entry displays the number of cells along each axis of the area of interest. As the Active volume cell sizes are modified, these figures are recalculated to fully enclose the original mesh volume. The time and cost to perform an inversion is directly related to the dimension of the mesh.
	Padded	The padded volumes are also displayed for your information.
[More]		Access advanced mesh settings.
[OK]		Proceed to the next step.

Expanded dialog options

Depth		The next six entries pertain to the vertical axis.
	Top of model	The maximum elevation of the terrain.
	Lin-log transition	The value along the vertical axis at which to transition to a logarithmic cell expansion.
	Bottom of model	The bottom of the voxel model along the vertical axis.
	Expansion ratio	The vertical increment is constant for all cells above the lowest point of the terrain. Below that level, the cell size increases with depth by this factor.
	Padding cells	Number of padding cells to add to the bottom of the voxel model. Padding is required; see note below.
	Padding expansion ratio	The intent of the padding cells is to minimize the edge effect in the predicted field. The padded cell size can be expanded when moving away from the active volume, in order to cover a larger area.
Horizontal Padding		The next two entries pertain to the horizontal (x and y) axes.
	Cells	Number of padding cells to add on either side of the x and y axes. Padding is required; see note below.
	Expansion ratio	The padding cells can be expanded at different rates along the horizontal and vertical axes.
Active Volume		The active volume extents are updated to reflect the changes to the above parameters.

Application Notes

By default, VOXI sets up the mesh according to the area of interest (AoI), the terrain relief and the user selected horizontal cell size. The VOXI model mesh is a 3D voxel model that represents Earth as a collection of adjacent voxel cells. The mesh is referred to as the Active Volume.

The Active Volume hangs below the terrain and extends downward to approximately half the minimum dimension of the area of interest, but should not exceed a reasonable exploration depth. In most cases, exploration becomes uneconomical below a couple of kilometres. Electrical methods generally have a lesser depth of penetration, thus the default vertical extent of the mesh is set accordingly.

The Mesh Parameters can be refined to better suit the targeted model. Bear in mind that reducing the cell size increases the size of the mesh, the time required to perform the computation, and the cost of the inversion.

Padding cells are added beyond the Active Volume laterally and at depth to make up the Padded volume. The padding cells serve to both minimize edge effects within your model and provide a way to model regional effects that may remain in your measurements. The expansion ratio of the horizontal and vertical axis can be set separately. For instance, along the direction of the predominant geologic structure, the expansion ratio can be larger than across it.

The active vertical cell size is set by default to one half of the smallest horizontal cell size. It will remain a constant until it reaches the lowest level of the terrain, below which, it will increase with depth by the depth expansion ratio to the maximum depth of the Active Volume.