Jump to content
RockWare Support Forum

Solid model plots


Mark Tarplee
 Share

Recommended Posts

I've plotted a geochemical dataset as a 3-D model using P-data (I'm treating it as point sample data). The dataset covers approx. 7x5 km but only 3-4m depth. Borehole top (surface) elevations extends from 40-115m. The resultant model seems to plot ok horizontally, though in options the highest metal concentration iso-level is about 25% of the maximum value in the dataset, even though this maximum value is displayed above. The surrounding cage extends vertically from 40-115m, in line with elevation. The problem is that the data interpolates vertically to the upper and lower bounding surfaces of the cage. I therefore don't get a true 3D solid model, more a 2D model stretched to an upper and lower planar surface (the cage). If I append a DEM with a bitmap drape, it bisects the solid model in the horizontal plane (the model plots both below and above it, cutting straight up through the DEM).

To solve the problem I created an upper and lower 'stratigraphic' layer in the form of elevation grids (makeshift DEM's) generated from the elevation values of the borehole tops. I added 1m to the elevation of the upper grid so that it would plot above the top of the borehole data. I made the lower grid 1m lower than the base of the boreholes so that it would plot beneath the base of the boreholes. I hoped that the model would interpolate to both the upper and lower 'constraining' surfaces thereby generating a realistic 3D solid model that could be appended beneath a DEM. When I applied the upper and lower .grds using the stratigraphic layer tool in the P-data model function, the resultant model looked entirely different from the one outlined in the first paragraph. The maximum iso-level was reduced to about 3% of the maximum value in the dataset and no more than 10% of what I would consider representative of the dataset. The plot was effectively constrained vertically as I required, but the horizontal plot was highly sporadic, intermittent and completely unrepresentative of the data values. It appears that sections of the data were missing or were not being properly interpolated between. In short the plot was entirely wrong. The only way I can restore a representative horizontal plot is to remove the upper and lower bounding .grds, which takes me back to square one.

All I want to do is plot a representative blob! I've tried changing the nodes, algorithms and horizontal/vertical weighting, all to no avail. Any suggestions?

It's hometime here in the UK but I'll be sure to acknowledge any suggestions tomorrow.

Cheers,

Mark.

Link to comment
Share on other sites

Mark:

It sounds like there are a number of problems.

1. The values in your model do not match your measured values. The cause of this is most likely your model spacing, although it is hard to know for sure about this without seeing the data. If you want your measured values to be honored exactly, then you need to decrease your spacing enough so that each control point resides in its own voxel (or 3D model cell).

Once you have reduced your model spacing sufficiently, turning on the Declustering options will also help because it centers your measured values in their corresponding voxels before running the interpolation algorithm. If you have done all of these things are still having no luck, then you also might consider turning on the High Fidelity option, however, keep in mind that this is only going to correct model "residuals" caused by interpolation averaging. This will not fix problems caused by situations where you have more than one measured point within a voxel.

Also, if you are concerned about your model values matching your measured values exactly, you should be sure to turn off the Smooth option when creating your model.

2. It sounds like your surfaces may be filtering out your measured high and low values. Before you run your model using the Stratabound option, I would suggest viewing both of your surfaces in 3D, along with your 3D data or boreholes. If you upper surface extends below portions of your data, or if your lower surface extends above portions of your data, it is going to be a problem.

You should follow the same rules when generating grids that you do when generating solid models. You typically always want your grid spacing to be small enough that you only have one measured point per grid cell. Also, if you are creating your surface grids with the Smooth option turned on, this could be the source of the problem.

If these suggestions do not help, I'd be happy to take a look at your data. Please contact me directly for directions on how to upload your data to our ftp site.

Regards,

Alison

Alison Alcott

RockWare, Inc.

alison@rockware.com

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...