Snap To Grid

by Nate Hekman on December 15, 2008

We generally recommend you always keep the “Snap to Grid” option on.  In fact in recent versions we’ve defaulted it to on for new files.  

The reason is that otherwise lines that appear to be vertical may in fact be slightly off. Many times that’s fine, but in SLOPE/W in particular nearly-vertical lines can cause a host of problems, and often be hard to detect.

So turn your grid on, and use these tips to draw foolproof geometry.

Grid Settings

Use the Grid Toolbar to make changes to your grid, or the Set – Grid menu item.

Use the Grid Toolbar for adjusting your grid as you work.

The button on the left turns the grid (and grid snapping) on or off.  

The two edit boxes adjust the grid spacing.  (You only need to adjust one of them–the other gets calculated automatically.)

Finer Detail

Adjust the grid spacing often as you work.  If you need to add details in between the grid points, don’t turn the grid off, just work with a finer grid.  When you’re done with detail area, you can make the grid coarser again.

Alt to Override the Grid

There are some times where you really need to work without the grid, or where you’re adjusting it so many times that you’d rather just turn it off.

Consider instead holding down the Alt key while you’re clicking.  The Alt key will temporarily override the grid, letting you click wherever you want.

{ 4 comments… read them below or add one }

1

Denise Leahy 01.27.09 at 10:06 am

Vertical lines in Slope/W:
– in earlier versions they were forbidden and nearly-vertical positively inclined lines were prefered;
– what is the problem with such nearly-vertical lines now?

The problem in earlier versions was often bad connection between adjacent soils but this is avoided by the recent versions using regions instead of lines, isn’t it?

2

Nate 01.27.09 at 10:48 am

You’re right, it used to be we recommended using nearly-vertical lines, because the solver couldn’t handle truly-vertical lines. But very thin slices can cause numerical instability, so that slight changes affect the computed factor of safety more than you’d expect. The best way all along was to properly handle vertical lines, and now SLOPE/W is able to do that.

A related problem when the grid is off is that two points that don’t belong to the same line (for example, one point from a geometry line and another from a water table) can end up being very close to each other in the x coordinate, which again creates a thin slice with potential side effects.

Most of the time such scenarios are fine, but when they do cause problems, they’re difficult to locate.

3

Nir Kumar Giri 03.05.09 at 10:10 pm

It is found difficult to exactly model the geometry of the slope in Slope/W. I would like to know that if we can model the geometry in Autocad and transfer to slope/W. In autocad we can exactly define the slope geometry or use the surveyed profile of the site.

NK Giri
DoR, Bhutan

4

Nate 03.06.09 at 8:51 am

The short answer is: yes, you can import from AutoCAD into SLOPE/W using the File – Import menu. Closed polygons in your DXF file will be converted to regions.

But there are some caveats! Although there is a place for importing a DXF, we also see lots of people get themselves in trouble doing it. The problem is that SLOPE/W really doesn’t need all that detail to give you a good answer. Modeling is a supposed to be a simplification of reality, and adding detail to the geometry does not necessarily give you more accurate results. Instead it can often make the analysis slower and the results more difficult to interpret.

Experienced modelers will more often start by importing the DXF file as a picture and drawing simple regions over top.

Leave a Comment

You can use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>