# Sampling surface at a fixed distance perpendicular to each surface's cell

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January 31, 2018, 06:16
Sampling surface at a fixed distance perpendicular to each surface's cell
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Hello,

I am new in openFoam.

I have a .openFoam project modeling flow over an island.
For the latter, I have converted a DEM into a .stl and used it in openFoam.

What I want to do now is to sample the model's results (e.g. Mean U, Pressure etc.) at 2 meters perpendicular to the surface (please forgive me for the low-quality image).

Trying to make it more clear, I am not looking to just increase Z by 2,
I want both X and Y to change accordingly, so that the new point has
Z so that the vertical distance from the surfaces is equal to 2 and perpendicular
to the cell of the surface that the points are located in.

I tried several different filters, and I think the "transform" filter
is closer to what I need. However, I cannot understand how to use the
translation and the scale parameters (if possible) to achieve what I need.

In essence, I think what I am looking for, is to sample normal to the surface
and at a fixed distance of 3 meters.

Any help will be much appreciated.

Thank you!
Attached Images
 tempTwoPointsPerpendicularToTheSurface.png (6.5 KB, 16 views)

Last edited by manos4u; February 1, 2018 at 10:40. Reason: extra clarification

 November 16, 2020, 14:45 #2 Member   Rishikesh Join Date: Apr 2016 Posts: 55 Rep Power: 6 Sorry to bump this but does anyone have an idea on this. I am looking to measure perpendicular distance to the VOF interface, which I assume to be the alpha = 0.5 contour. It is however not a searchable surface. If I couple a level-set at the said contour and then solve for it, I can get a gradient field which will give the said value. However, this operation is computationally expensive and slows down the process considerably. Any suggestions towards a simpler method to extract perpedicular distance from the contour would be appreciated.

 November 29, 2020, 13:55 #3 Senior Member   Mark Olesen Join Date: Mar 2009 Location: https://olesenm.github.io/ Posts: 1,168 Rep Power: 29 Would need to see what is missing, but extracting an iso-surface gives you a meshed surface that should also be closed. Searchable surfaces have a triSurfaceMesh form that you should be able to use to wrap the iso-surface.

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