SpatialFieldManager

Dim doc As Document = commandData.Application.ActiveUIDocument.Document
Dim uiDoc As UIDocument = commandData.Application.ActiveUIDocument

Dim sfm As SpatialFieldManager = SpatialFieldManager.GetSpatialFieldManager(doc.ActiveView)
If sfm Is Nothing Then
   sfm = SpatialFieldManager.CreateSpatialFieldManager(doc.ActiveView, 1)
End If
Dim reference As Reference = uiDoc.Selection.PickObject(ObjectType.Face, "Select a face")
Dim idx As Integer = sfm.AddSpatialFieldPrimitive(reference)

Dim face As Face = TryCast(doc.GetElement(reference).GetGeometryObjectFromReference(reference), Face)

Dim uvPts As IList(Of UV) = New List(Of UV)()
Dim bb As BoundingBoxUV = face.GetBoundingBox()
Dim min As UV = bb.Min
Dim max As UV = bb.Max
uvPts.Add(New UV(min.U, min.V))
uvPts.Add(New UV(max.U, max.V))

Dim pnts As New FieldDomainPointsByUV(uvPts)

Dim doubleList As New List(Of Double)()
Dim valList As IList(Of ValueAtPoint) = New List(Of ValueAtPoint)()
doubleList.Add(0)
valList.Add(New ValueAtPoint(doubleList))
doubleList.Clear()
doubleList.Add(10)
valList.Add(New ValueAtPoint(doubleList))

Dim vals As New FieldValues(valList)
Dim resultSchema As New AnalysisResultSchema("Schema Name", "Description")
Dim schemaIndex As Integer = sfm.RegisterResult(resultSchema)
sfm.UpdateSpatialFieldPrimitive(idx, pnts, vals, schemaIndex)