Maya get closest vertex

getClosestVertex.py

import maya.api.OpenMaya as om
import maya.cmds as cmds

#returns the closest vertex given a mesh and a position [x,y,z] in world space.
#Uses om.MfnMesh.getClosestPoint() returned face ID and iterates through face's vertices.
def getClosestVertex(mayaMesh,pos=[0,0,0]):
    mVector = om.MVector(pos)#using MVector type to represent position
    selectionList = om.MSelectionList()
    selectionList.add(mayaMesh)
    dPath= selectionList.getDagPath(0)
    mMesh=om.MFnMesh(dPath)
    ID = mMesh.getClosestPoint(om.MPoint(mVector),space=om.MSpace.kWorld)[1] #getting closest face ID
    list=cmds.ls( cmds.polyListComponentConversion (mayaMesh+'.f['+str(ID)+']',ff=True,tv=True),flatten=True)#face's vertices list
    #setting vertex [0] as the closest one
    d=mVector-om.MVector(cmds.xform(list[0],t=True,ws=True,q=True))
    smallestDist2=d.x*d.x+d.y*d.y+d.z*d.z #using distance squared to compare distance
    closest=list[0]
    #iterating from vertex [1]
    for i in range(1,len(list)) :
        d=mVector-om.MVector(cmds.xform(list[i],t=True,ws=True,q=True))
        d2=d.x*d.x+d.y*d.y+d.z*d.z
        if d2<smallestDist2:
            smallestDist2=d2
            closest=list[i]      
    return closest

Thanks - saved me some time to quickly test a thing.

Here's a quick cleanup/rewrite as thanks!

from maya import cmds
import maya.api.OpenMaya as om
import operator


def getClosestVertex(mesh, pos=(0,0,0)):
    """Return closest vertex and distance from mesh to world-space position [x, y, z].
        
    Uses om.MfnMesh.getClosestPoint() returned face ID and iterates through face's vertices.
    
    Example:
        >>> getClosestVertex("pCube1", pos=[0.5, 0.5, 0.5])
        # (3, 0.0)
        >>> getClosestVertex("pCube1", pos=[0.5, 0.9, 0.5])
        # (3, 0.4)

    Args:
        mesh (str): Mesh node name.
        pos (list): Position vector XYZ
        
    Returns:
        tuple: (vertex index, distance)
    
    """
    pos = om.MPoint(pos)
    sel = om.MSelectionList()
    sel.add(mesh)
    fn_mesh = om.MFnMesh(sel.getDagPath(0))
    
    index = fn_mesh.getClosestPoint(pos, space=om.MSpace.kWorld)[1]  # closest polygon index    
    face_vertices = fn_mesh.getPolygonVertices(index)  # get polygon vertices
    
    vertex_distances = ((vertex, fn_mesh.getPoint(vertex, om.MSpace.kWorld).distanceTo(pos)) 
                         for vertex in face_vertices)
    return min(vertex_distances, key=operator.itemgetter(1))