Anisotropy in Gslib
I'm using iTough2 and am trying to create a heterogeneous field using gslib. I could not actualy figure it out what is the definition of the ang2 and how to define the anisotropy ratios. I mean, it is said that ang2 is measured in negative degrees down from the horizontal. Does it mean that ang2 should always be negative or the code will pick the number as a negative value? (In the sample exercise it is 70)
Also, based on the definition given for anisotropy ratios, shouldn't they be less than one? (They are 5 in the sample exercise
The definitions come straight from the GSLIB User's Guide. I find them confusing as well. I propose you simply generate a field with a given angle and anisotropy factor and visualize it - this will clearly show the orientations. Anisotropy factors are just ratios, so they could be greater or smaller than 1.0. Note that they may give the appearance that the angle is rotated by 90 degrees if you don't carefully look at the definition of the ratio. Also note that there are many ways to define angles (and there are different conventions depending on the field, i.e., geology, land surveying, mathematics, ...) - so again: the best way to make sure the heterogeneous permeability field generated by GSLIB is consistent with your expectations is to visualize it.