Interactively select one or more vertices from an rgl surface.
vertexSelect(object = first(rgl::rgl.ids()$id), tolerance = 0.01, multiples = FALSE, indicate = TRUE)
| object | An rgl id for the object from which to choose vertices. Defaults to the first id. To check the ids available for selection call rgl.ids() unfortunately there is no elegant way at the present for determining which object is which. |
|---|---|
| tolerance | The tolerance, in fractions of the visible window, for finding points. See details for more. |
| multiples | Whether to stop after the first selection, or to allow multiples (explicitly stopped by pressing escape). |
| indicate | Whether to draw indicator points to highlight the clicked points. Useful for ensuring point click accuracy. |
The vertex selection algorithm has two parts, selecting the vertices near the clicked point
and determining which points are closest to the observer.
To determine the vertices near the click point
Determine the x-y coordinates of the click in window space
Convert those coordinates to a rectangle defined by (x - tolerance, y - tolerance, x + tolerance, y + tolerance)
Convert the rectangle coordinates from window to user coordinates
Filter the vertices of the object within the rectangle
To determine the vertex closest to observer
Determine the x-y click location
Append z=0 to the coordinates to create a 3d window coordinate, since the rgl observe looks in the positive z direction, a window z coordinate of zero puts the point as far from the surface as possible while remaining in the window coordinates
Convert from window to user coordinates
Calculate the vertex from the set identified above that is closest to those coordinates
This algorithm is not perfect, and can yeild spurious coordinates for irregular topologies. For more accurate vertex selection, use a high magnification (controlled with the scroll wheel), the higher the magnification the more accurate the vertex selection becomes. Additionally, keep indicate = TRUE, this will place indicator points on the identified vertices, they will allow you to ensure your coordinates are accurate, and can always be removed with pop3d()