Automating the processing of geospatial data in a Geographic Information System (GIS) using VBA in Excel

Automating the processing of geospatial data in a Geographic Information System (GIS) using VBA in Excel can be a challenging task, especially when interacting with specific GIS formats like shapefiles or spatial databases. However, it is possible to automate certain tasks from Excel, such as manipulating geographic attribute data, and integrating with GIS tools like QGIS or ArcGIS using external APIs.

In this example, we will demonstrate how to automate geospatial data processing tasks with VBA, assuming you already have a file containing geospatial data, such as coordinates or attribute information, in an Excel file.

Objective:

Automate the process of cleaning and analyzing geospatial data (for example, calculating the distance between two geographic points).

Prerequisites:

1. An Excel file with columns for latitude and longitude of geographic points.
2. Using VBA to calculate the distance between two points using their geographic coordinates.

Excel File Structure

Let’s assume your Excel file contains the following data:

• Latitude and longitude are stored as decimal numbers.
• You want to calculate the distance between these two points in kilometers.

Calculating Distance Between Two Geographic Points (Haversine Formula)

We will use the Haversine Formula to calculate the distance between two points on the Earth’s surface based on their latitude and longitude.

VBA Code

Here’s the VBA code to automate this process:

Option Explicit
' Constants for Earth
Const R As Double = 6371 ' Earth's radius in kilometers
' Function to convert degrees to radians
Function DegreesToRadians(degree As Double) As Double
    DegreesToRadians = degree * (WorksheetFunction.Pi() / 180)
End Function
' Function to calculate the distance between two geographic points
Function CalculateDistance(Lat1 As Double, Lon1 As Double, Lat2 As Double, Lon2 As Double) As Double
    ' Convert latitudes and longitudes to radians
    Lat1 = DegreesToRadians(Lat1)
    Lon1 = DegreesToRadians(Lon1)
    Lat2 = DegreesToRadians(Lat2)
    Lon2 = DegreesToRadians(Lon2)   
    ' Calculate differences
    Dim dLat As Double
    Dim dLon As Double
    Dim a As Double
    Dim c As Double
    dLat = Lat2 - Lat1
    dLon = Lon2 - Lon1
    a = Sin(dLat / 2) * Sin(dLat / 2) + Cos(Lat1) * Cos(Lat2) * Sin(dLon / 2) * Sin(dLon / 2)
    c = 2 * Atan2(Sqr(a), Sqr(1 - a))
    ' Return distance in kilometers
    CalculateDistance = R * c
End Function
' Subroutine to process geospatial data in Excel
Sub ProcessGeospatialData()
    Dim i As Integer
    Dim Latitude1 As Double, Longitude1 As Double
    Dim Latitude2 As Double, Longitude2 As Double
    Dim Distance As Double   
    ' Start from row 2 to skip header
    For i = 2 To Cells(Rows.Count, 1).End(xlUp).Row
        Latitude1 = Cells(i, 3).Value
        Longitude1 = Cells(i, 4).Value
        Latitude2 = Cells(i + 1, 3).Value ' Next point
        Longitude2 = Cells(i + 1, 4).Value ' Next point       
        ' Calculate the distance between the two points
        Distance = CalculateDistance(Latitude1, Longitude1, Latitude2, Longitude2)       
        ' Output the distance in column 5 (distance in kilometers)
        Cells(i, 5).Value = Distance
    Next i   
    MsgBox "Geospatial data processing is complete.", vbInformation
End Sub

Explanation of the Code:

1. Defining Constants:

• Const R As Double = 6371: This is the radius of the Earth in kilometers.

2. DegreesToRadians Function:

This function converts the geographic coordinates (latitude and longitude) from degrees to radians because trigonometric functions in VBA require radians.

3. CalculateDistance Function:

This function implements the Haversine Formula to calculate the distance in kilometers between two points. It accepts the latitude and longitude of both points as arguments and returns the calculated distance.

4. ProcessGeospatialData Subroutine:

• This subroutine loops through the data in the Excel sheet (starting from row 2 to skip the header), retrieves the latitude and longitude coordinates from columns 3 and 4, and calculates the distance between each point and the next one.
• The distance is then displayed in column 5 of the Excel sheet.

4. Using the Code

1. Open Excel and press Alt + F11 to open the VBA editor.
2. In the editor, click Insert > Module and paste the code above.
3. Go back to the Excel sheet, then press Alt + F8 to run the macro ProcessGeospatialData.

This will populate column 5 with the distance between each point and the next, in kilometers.

5. Additional Steps:

• Importing GIS Data: For more advanced processing with shapefiles or spatial databases (like PostGIS), you may need to use tools like QGIS or ArcGIS with Python scripts, which goes beyond VBA capabilities. However, you can automate the export of data to Excel and then perform calculations or geospatial analysis within Excel.
• GIS Visualization in Excel: You can also create maps within Excel by plotting points on a scatter plot or using specialized add-ins for geospatial mapping.

Conclusion:

This VBA code allows you to automate a simple process of calculating the distance between two geographic points in an Excel file. For more advanced analysis, integrating with a dedicated GIS software like QGIS or ArcGIS would be more suitable.