This can be accomplished by adding a spherecast to the cylinder and when any object enters it ( a box collider, raycast, etc ) have some event occur. For detecting the triangles of the plane ( assuming you have some sort of mesh collider ) you can get a list of all hit objects within the cylinder's spherecast and cycle through each one that composes a complete mesh triangle. Here's some code to show the process:
void GetMeshTriangle( RaycastHit meshHitPoint, MeshCollider meshObject ){
Mesh mesh = meshObject.sharedMesh;
Vector3[] vertices = mesh.vertices;
int[] triangles = mesh.triangles;
int counter = 0;
for( int n = 0; n <= ( worldObjectsHit.Length * 3 ); n++ ){
if ( counter == 2 ){
Transform hitTransform = meshHitPoint.collider.transform;
try{
Vector3 pointOne = vertices[triangles[meshHitPoint.triangleIndex * 3 + n]];
Vector3 pointTwo = vertices[triangles[meshHitPoint.triangleIndex * 3 + ( n-1 )]];
Vector3 pointThree = vertices[triangles[meshHitPoint.triangleIndex * 3 + ( n-2 )]];
pointOne = hitTransform.TransformPoint( pointOne );
pointTwo = hitTransform.TransformPoint( pointTwo );
pointThree = hitTransform.TransformPoint( pointThree );
Vector3 meshObjectCenter = new Vector3( ( ( pointOne.x + pointTwo.x + pointThree.x ) / 3 ),
( ( pointOne.y + pointTwo.y + pointThree.y ) / 3 ) ,
( ( pointOne.z + pointTwo.z + pointThree.z ) / 3 ) );
Debug.DrawLine( p0, p1 );
Debug.DrawLine( p1, p2 );
Debug.DrawLine( p2, p0 );
IsMeshColliding( meshHitPoint, meshObjectCenter );
} catch ( System.IndexOutOfRangeException ex ){
break;
}
counter = 0;
} else {
counter++;
}
}
}
At the line "IsMeshColliding( )" you can add in your own logic to have some sort of event occur.