Determine the Maximum Z Coordinate Value of a Surface
Windows only

Demonstrates how determine the maximum Z coordinate value of a surface or polysurface given some X,Y coordinate.

CRhinoCommand::result CCommandTest::RunCommand( const CRhinoCommandContext& context )
{
double x = 0.0, y = 0.0;
ON_wString sx, sy, sz;

// Pick a brep to evaluate
CRhinoGetObject go;
go.SetCommandPrompt( L"Select surface or polysurface to evaluate" );
go.SetGeometryFilter( CRhinoGetObject::surface_object|CRhinoGetObject::polysrf_object );
go.GetObjects( 1, 1 );
if( go.CommandResult() != success )
return go.CommandResult();

// Get the brep geometry
const CRhinoObjRef& ref = go.Object(0);
const ON_Brep* brep = ref.Brep();
if( !brep )
return failure;

// Prompt for an X coordinate value
CRhinoGetNumber gn;
gn.SetCommandPrompt( L"Value of X coordinate" );
gn.SetDefaultNumber( x );
gn.GetNumber();
if( gn.CommandResult() != success )
return gn.CommandResult();

x = gn.Number();
RhinoFormatNumber( x, sx );

// Prompt for a Y coordinate value
gn.SetCommandPrompt( L"Value of Y coordinate" );
gn.SetDefaultNumber( y );
gn.GetNumber();
if( gn.CommandResult() != success )
return gn.CommandResult();

y = gn.Number();
RhinoFormatNumber( y, sy );

// Now that we have all of the input, we want to intersect
// a line curve with the brep. To determine the magnitude of
// the line, we will first get the brep's bounding box.
ON_BoundingBox bbox;
if( !brep->GetTightBoundingBox(bbox) )
return failure;

// Calculate the height of the bounding box
ON_3dVector v = bbox.Corner(0,0,1) - bbox.Corner(0,0,0);

// Starting point of line
ON_3dPoint p0( x, y, 0.0 );

// Ending point of line. To make sure the line
// completely intersects the brep, we will double
// the height.
ON_3dPoint p1( x, y, v.Length() * 2 );

// Create the line curve
ON_LineCurve line( p0, p1 );

// Intersect the line with the brep
ON_SimpleArray<ON_Curve*> curves;
ON_3dPointArray points;
bool rc = RhinoCurveBrepIntersect( line, *brep, context.m_doc.AbsoluteTolerance(), curves, points );
if( false == rc | 0 == points.Count() )
{
RhinoApp().Print( L"No maximum surface Z coordinate at %s,%s found.\n", sx, sy );
return nothing;
}

// Because it is possible that our line might intersect
// the brep in more than one place, find the intersection
// point that is farthest from our input coordinate.
int i;
ON_3dPoint pt = p0;
for( i = 0; i < points.Count(); i++ )
{
if( p0.DistanceTo(points[i]) > p0.DistanceTo(pt) )
pt = points[i];
}

// Print results
RhinoFormatNumber( pt.z, sz );
RhinoApp().Print( L"Maximum surface Z coordinate at %s,%s is %s.\n", sx, sy, sz );

// Optional, add a point object