# HydroGeoSphere/Selecting Inclined Faces

*These instructions only work for rectangular meshes with the standard element numbering scheme.*

## Inclined Face ID NumbersEdit

For each block element, there are 6 potential inclined faces which may be selected. These are given ID numbers according to the following convention:

```
PLANE ID LOCAL NODES
1 1-2-7-8
2 4-3-6-5
3 2-3-8-5
4 1-4-7-6
5 1-3-7-5
6 2-4-8-6
```

## Clear chosen inclined facesEdit

All faces in the domain are flagged as *not* chosen. This is recommended if you are unsure of which inclined faces are chosen due to previously issued instructions.

Note that this instruction also clears chosen regular (horizontal and vertical) faces. This is necessary because a previously defined inclined plane may also consist of horizontal or vertical faces which have to be unselected as well.

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## Choose faces 3pt inclined planeEdit

**nplane**Plane ID number, as defined above.**x1, y1, z1***xyz*-coordinates of the first point on the plane.**x2, y2, z2***xyz*-coordinates of the second point on the plane.**x3, y3, z3***xyz*-coordinates of the third point on the plane.**ptol**Distance from the plane.**xmin, xmax***x*-range of the block.**ymin, ymax***y*-range of the block.**zmin, zmax***z*-range of the block.

Faces which have the appropriate plane ID, whose centroids lie within the distance **ptol** of the plane which is defined by the 3 points, and whose centroids are within the rectangular block defined by the 3 ranges are chosen.

Note that if the plane defined by the 3 points is parallel to one coordinate axis, the preprocessor will automatically use the ID of the plane parallel to that axis, and the user-defined plane ID will be ignored.

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