如何获得整个文档的BoundingBox？

Public Function ssExtents(ss As AcadSelectionSet) As Variant
    Dim points(), c As Long
    Dim min, max, util As AcadUtility
    
    Set util = ThisDrawing.Utility
    
    c = 0
    
    For i = 0 To ss.Count - 1
        
        ss.Item(i).GetBoundingBox min, max
        min = util.TranslateCoordinates(min, acWorld, acUCS, False)
        max = util.TranslateCoordinates(max, acWorld, acUCS, False)
        ReDim Preserve points(0 To c + 1)
        points(c) = min: points(c + 1) = max
        c = c + 2
        
    Next
        
    ssExtents = Extents(points)
End Function 
Public Function Extents(points)
    Dim min, max
    Dim i As Long, j As Long, pt, retVal(0 To 1)
    
    min = points(LBound(points))
    max = points(LBound(points))
        
    For i = LBound(points) To UBound(points)
        pt = points(i)
        For j = LBound(pt) To UBound(pt)
            If pt(j)  max(j) Then max(j) = pt(j)
        Next
    Next
    
    retVal(0) = min: retVal(1) = max    
    Extents = retVal
End Function

Sub test()
    ' 图中没有实体时不做处理
    If ThisDrawing.ModelSpace.Count = 0 Then Exit Sub
    ' 按图中实体的最大范围缩放
    Application.ZoomExtents
    ' 窗口的中心点坐标
    Dim cPt As Variant
    cPt = ThisDrawing.GetVariable("VIEWCTR")
    ' 窗口的高度
    Dim h As Double
    h = ThisDrawing.GetVariable("VIEWSIZE")
    
    ' 窗口的宽度
    Dim w As Double
    Dim s As Variant
    s = ThisDrawing.GetVariable("SCREENSIZE")
    w = h * s(0) / s(1)
    
    ' 窗口的左下角和右下角坐标
    Dim minExt(0 To 2) As Double
    Dim maxExt(0 To 2) As Double
    minExt(0) = cPt(0) - w / 2: minExt(1) = cPt(1) - h / 2: minExt(2) = 0
    maxExt(0) = cPt(0) + w / 2: maxExt(1) = cPt(1) + h / 2: maxExt(2) = 0
End Sub

Sub test()
    ' 图中没有实体时不做处理
    If ThisDrawing.ModelSpace.Count = 0 Then Exit Sub
    
    ' 按图中实体的最大范围缩放
    Application.ZoomExtents
    
    ' 窗口的左下角和右下角坐标
    Dim minExt As Variant
    Dim maxExt As Variant
    minExt = ThisDrawing.GetVariable("EXTMIN")
    maxExt = ThisDrawing.GetVariable("EXTMAX")
End Sub