A customer wrote: pgf vs geo (why geo?)

I am serving as a team lead for a group of EVS users. I had a meeting with one of our team members this morning. He was having issues with his model; per the training he did he informed me that his understanding was that that he “had” to use make_geo_hierarchy to produce the geology file he needed. I recommended that he simply use the pgf format. He asked “well what is the need for a geo file then?” Other than providing stratigraphic ordering I was unable to provide an adequate answer. So, …What utility, other than stratigraphy, does the geo file structure offer us that the pgf file type does not? Because the results I get with pgf and smooth indicator_geology are so consistently “good”, I have since abandoned geo files altogether.

The customer is correct, that .GEO (and .GMF) are exclusively needed for stratigraphic geologic modeling.  Though I agree that the results I get with smooth lithologic modeling are awesome and I also rarely now turn to stratigraphic modeling, there are some advantages to stratigraphic modeling, when it does apply to your site data, and in those cases I do believe that the extra effort of using make_geo_hierarchy to create the .GEO file is warranted.
For example:
  • If you know you are dealing with sedimentary geology and you have relatively few borings OR a region in the site where there are no borings, stratigraphic modeling will likely honor the site geology better.
  • Stratigraphic modeling gives you true “layers” and therefore the ability to have Layer Thickness.   Lithologic modeling has no “layers”….only materials and no concept of thickness.
  • Stratigraphic layers explode (apart) in a more natural (logical) manner, even when there are pinched layers and lenses.
  • Though I acknowledge the lack of a training video (or workbook) on this subject (it is in the works), stratigraphic modeling has the edit_horizons module which when used together with texture_cross_sections provides the ability to hand-edit stratigraphic layers to force them to match hand-drawn cross-sections and/or just to make minor modifications to pinched-out regions or horizon extrapolations.