public MapPoint GetPoint( 
   int pointIndex
)

Coordinate2D[] coordinate2Ds = new Coordinate2D[] { new Coordinate2D(1, 2), new Coordinate2D(-1, -2) };
SpatialReference sr = SpatialReferences.WGS84;

MultipointBuilderEx builder = new MultipointBuilderEx(coordinate2Ds, sr);

// builder.PointCount = 2

builder.HasZ = true;
// builder.Zs.Count = 2
// builder.Zs[0] = 0
// builder.Zs[1] = 0

builder.HasM = true;
// builder.Ms.Count = 2
// builder.Ms[0] = NaN
// builder.Ms[1] = NaN

builder.HasID = true;
// builder.IDs.Count = 2
// builder.IDs[0] = 0
// builder.IDs[1] = 0

// set it empty
builder.SetEmpty();
// builder.Coords.Count = 0
// builder.Zs.Count = 0
// builder.Ms.Count = 0
// builder.IDs.Count = 0


// reset coordinates
List<Coordinate2D> inCoords = new List<Coordinate2D>() { new Coordinate2D(1, 2), new Coordinate2D(3, 4), new Coordinate2D(5, 6) };
builder.Coordinate2Ds = inCoords;
// builder.Coords.Count = 3
// builder.HasZ = true
// builder.HasM = true
// builder.HasID = true

double[] zs = new double[] { 1, 2, 1, 2, 1, 2 };
builder.Zs = zs;   
// builder.Zs.Count = 6

double[] ms = new double[] { 0, 1 };
builder.Ms = ms;   
// builder.Ms.Count = 2

// coordinates are now   (x, y, z, m, id)
//  (1, 2, 1, 0, 0), (3, 4, 2, 1, 0) (5, 6, 1, NaN, 0)

MapPoint mapPoint = builder.GetPoint(2);
// mapPoint.HasZ = true
// mapPoint.HasM = true
// mapPoint.HasID = true
// mapPoint.Z  = 1
// mapPoint.M = NaN
// mapPoint.ID = 0

// add an M to the list
builder.Ms.Add(2);
// builder.Ms.count = 3

// coordinates are now   (x, y, z, m, id)
//  (1, 2, 1, 0, 0), (3, 4, 2, 1, 0) (5, 6, 1, 2, 0)

// now get the 2nd point again; it will now have an M value
mapPoint = builder.GetPoint(2);
// mapPoint.M = 2


int[] ids = new int[] { -1, -2, -3 };
// assign ID values
builder.IDs = ids;

// coordinates are now   (x, y, z, m, id)
//  (1, 2, 1, 0, -1), (3, 4, 2, 1, -2) (5, 6, 1, 2, -3)


// create a new point
MapPoint point = MapPointBuilderEx.CreateMapPoint(-300, 400, 4);
builder.SetPoint(2, point);

// coordinates are now   (x, y, z, m, id)
//  (1, 2, 1, 0, -1), (3, 4, 2, 1, -2) (-300, 400, 4, NaN, 0)


builder.RemovePoints(1, 3);
// builder.PointCount = 1

// assume a multiPoint has been built from 4 points
// the modified multiPoint will have the first point removed and the last point moved

// use the builderEx constructors which don't need to run on the MCT.
MultipointBuilderEx builderEx = new MultipointBuilderEx(multipoint);
// remove the first point
builderEx.RemovePoint(0);
// modify the coordinates of the last point
var ptEx = builderEx.GetPoint(builderEx.PointCount - 1);
builderEx.RemovePoint(builderEx.PointCount - 1);

var newPtEx = MapPointBuilderEx.CreateMapPoint(ptEx.X + 1.0, ptEx.Y + 2.0);
builderEx.AddPoint(newPtEx);
Multipoint modifiedMultiPointEx = builderEx.ToGeometry() as Multipoint;