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.