How does snapping for offset from surface work?

KarenFu Posts: 3 Calcite Rank Badge
I was trying to model a fill layer by creating a deposit surface through offsetting from topography and adding contact points from BH.

Some of my fill is only 1m thick and in some area it is up to 30m thick. 

I have 100% snapping turned on for BH data and did not set any min/max offset distance. 

However, I noted the output would not snap to all the contact points, it is because there is too much of a variation between my contact points?

I have done something similar to model the rockhead as well, but similarly not all contact points are snapped. 

Best Answer

  • SamChappell
    SamChappell Posts: 6 admin
    Answer ✓
    Hi Karen, we had a look into this and here are some possible explanations:

    Enabling snapping does not necessarily mean the surface will snap to all input data. 

    The snapping behaviour is influenced by surface resolution, maximum snap distance, smoothing and whether or not adaptive surfacing is checked on. 

    A surface will not snap to all borehole data if - 
    • Two or more borehole contacts are too close to each other. "Too close" is typically 1/5th of the mesh resolution, so a surface with a resolution of 5 will not snap to two data points less than 1 unit apart 
    • Some of the borehole contacts are too far away from the surface (outside of the maximum snap distance).

    A surface may not snap to all borehole data if - 
    • Adaptive is checked on for the surface. Adaptive surfacing uses a different subdivision algorithm which can prioritise the shape of the reference mesh over the inputs
    • High smoothing is applied.

    If you are still having issues, please can you reach out to support so we can look into your project with you:


  • KarenFu
    KarenFu Posts: 3 Calcite Rank Badge

    Hi Sam, thanks for the reply!

    Just wondering, when you say using adaptive surfacing could make the surface not snap to borehole data. Does this happen for the standard deposit surface from base interval as well, when there is not a reference mesh. As I tends to like using adaptive, believing it would allow finer mesh resolution when data density is high.

  • SamChappell
    SamChappell Posts: 6 admin

    Hi Karen,

    You are correct that adaptive allows a finer mesh resolution where data density is high. Adaptive offset surfaces behave a little differently from other adaptive surfaces, as the offset mesh is trying to follow the reference mesh as well as any 'snap to' data. Other adaptive surfaces (such as a deposit surface with adaptive turned on) should snap to data as expected, provided the input data are not too close together and within the snap distance.