Xmgr: region operations

## Region operations

- Define region
- Evaluate in region
- Clear region
- Extract points
- Delete points
- Area/perimeter

### Define region

Define a region of interest on a graph or graphs.

Select the region, there are 5.

Select the type of region:

Inside polygon
  Points inside a closed, non-intersecting polygon are considered inside the region.

Outside polygon
  Points outside a closed, non-intersecting polygon are considered inside the region.

Above, below, to the left, and to the right
  Regions defining a half-plane, points inside the half-plane are considered in the region.

Select the type of linkage, either a particular graph or all graphs, the default is the current graph.

Press Accept to make the pointer ready for the region definition. In the polygonal region type, define the region by successive clicks with the left mouse button, use the right mouse button to register the polygon. In the line case, define the line by clicking on the beginning point and end point of the line.

### Evaluate in region

Evaluate an expression applied to points within a region.

Select the region to use.

Enter the expression, regions are referred to by Rn.x or Rn.y where `n' is the number of the region to use. Functions available are the same as those in `Evaluate expressions' described above.

Examples:

R0.X = R0.X - 1

### Clear region

Remove a defined region.

Select the region to remove and press `Apply'.

### Extract points

Extract points from a region to a set

Select the region to use.

Select the set to receive the points.

Select the graph to put the set.

Click on Accept to combine all points within the specified region to the specified set and graph.

### Delete points

Delete points in a region.

Select the region to use.

Click on Accept to delete all points in all sets within the specified region.

### Area/perimeter

Compute the area and perimeter of a region. This item doesn't belong here as it does not use the region structures. Click on Area or Perimeter and use the mouse to define the region. The area or perimeter will be displayed in the text items Area = or Perimeter = whichever the case may be. Use the right mouse button to close the region.