If you created or received a BLN file which results in an error upon import into Surfer, the vertex count defined in the object header is often the culprit.  The script below counts the vertices in each object of a BLN and updates the header count value appropriately.

To run this script:

1. Copy the script below, download the attached BAS file: BLNheader.bas.
2. In a Windows Explorer window, navigate to C:\Program Files\Golden Software\Surfer.
3. Double click on Scripter.exe to launch Scripter.
4. Press Ctrl+A to select all of the existing lines then press Delete.
5. If you copied this script, press Ctrl+V to paste it into Scripter. If you downloaded it, click File | Open, select the BAS file from your downloads directory, and click Open.
6. Click Script | Run to run the script.
    

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'This script searches the BLN file using the BLN flag value in
'Column B and then automatically enters the correct number of points
'in the header line in Column A. This is useful if you have a long
'BLN file and the header count is off for a few objects.
'============================================================

Sub Main
    Debug.Clear
    Dim SurferApp As Object
    Set SurferApp = CreateObject("Surfer.Application")
    SurferApp.Visible = True

    'Specifies input data
    BLNFile$ = GetFilePath( , "bln",path1, "Select bln file")
    If BLNFile$ ="" Then End

    'Opens BLN file
    Dim Wks As Object
    Set Wks = SurferApp.Documents.Open(FileName:=BLNFile$)

    'Defines worksheet range as columns A and B
    Dim WksRange As Object
    Set WksRange = Wks.Columns(Col1:=1, Col2:=2)

    'Define the header flag in Column B for the objects in the BLN file
    Flag= Val(InputBox$("Enter the flag value in Column B in the BLN file. It must be the same for each object in the BLN. Usually, this is a 0 or 1.", "Specify Flag Value", "1"))

    'Sets BLN header
    RowToChange = 0
    For row=1 To WksRange.RowCount
        'If Grid.IsBlanked(row,col) = True Then Grid.SetNode(row,col) = 0
        If Wks.Cells("B"+Format(row)).Value=Flag Then
            If RowToChange >0 Then
                Wks.Cells("A"+ RowToChange).Value = Format(row)-RowToChange-1
            End If
            RowToChange = Format(row)
        End If
        If Format(row) = WksRange.RowCount Then
            Wks.Cells("A"+RowToChange).Value = Format(row)-RowToChange
        End If
    Next row

    'Saves BLN file
    BLNfilepath = Left(BLNFile$,InStrRev(BLNFile$,".")-1) + "_Corrected.bln
    Wks.SaveAs(FileName:=BLNfilepath)
    Debug.Print "File saved as ";BLNfilepath
End Sub

Updated November 2021