Calculate a distance from a known point to a series of polygon centroids

Summary

You can use Avenue to calculate a distance from a known point to a series of polygon centroids. This is an example of coding using the Avenue requests: ReturnCenter, GetX, GetY, and SqRt.

Procedure

1. Open a New Script window.
2. Copy and paste this code:
   
   

   Code:
   '-- Calculating Distance Script
   
   '-- This script requires:
   '-- 1. A polygon theme in the view
   '-- 2. A field called 'zipcode' in the attribute table
   
   TheView = av.GetActiveDoc
    theThm = theView.GetActiveThemes.Get(0)
    thl = theThm.GetFtab
    thl.SetEditable(TRUE)
   
    if (thl.FindField("zipcode") = nil) then
     MsgBox.Error("zipcode field does not exist","")
     exit
    end
   
   '-- Get search point location
   
    fldval = MsgBox.Input("Enter the Target ZipCode","Target ZipCode","")
     MsgBox.Info(fldval,"")
   
    s = 0
    zipfld = thl.FindField("zipcode")
    shpfld = thl.FindField("shape")
   
    found = "no"
   
    for each n in thl
   
    if ((thl.ReturnValue(zipfld,s).AsString = fldval)) then
     poly = thl.ReturnValue(shpfld,s)
     polps = poly.ReturnCenter
     xcord = polps.GetX
     ycord = polps.GetY
     found = "yes"
    end
    s = s + 1
    end
   
    if (found = "no") then
     MsgBox.Error("Can't find the Zip id you entered","")
     exit
    end
   
   '-- Check for the existence of fields
    fldnames = thl.GetFields
    count = 0
    for each x in fldnames
      if (x.AsString = "xcord") then
         count = count + 1
      end
        if (x.AsString = "ycord") then
           count = count + 1
        end
      if (x.AsString = "Distance") then
         count = count + 1
      end
    end
   
    if ((count = 1) or (count = 2)) then
     MsgBox.Error("The file "+thl.AsString+"+NL+
   some but not all of the fields needed. You must create them manually","")
     exit
    end
   
    if (count = 3) then
    xcords = thl.FindField("xcord")
    ycords = thl.FindField("ycord")
    Dist = thl.FindField("Distance")
    end
   
   '-- Create the xcord, ycord, Distance fields and add them to shape file
    if (count <> 3) then
    xcords = Field.Make("xcord",#FIELD_DECIMAL,16,6)
    ycords = Field.Make("ycord",#FIELD_DECIMAL,16,6)
    Dist = Field.Make("Distance",#FIELD_DECIMAL,16,6)
    FldLst = {xcords,ycords,Dist}
    thl.AddFields(FldLst)
    end
   
    n = 0
   
   '-- Perform field calculations
    plyFtab = Thethm.GetFtab.FindField("shape")
   
    for each n in thl
   
   '-- Find the shape field and return its value "polygon"
    what = theThm.getFtab.ReturnValue(plyFtab,n)
   
   '-- Get the x and y value of the centers of each polygon
    pnts = what.ReturnCenter
    xnum = pnts.GetX
    ynum = pnts.GetY
   
   '-- Set the x and y of the center to a record number
    theThm.GetFtab.SetValue(xcords,n,xnum)
    theThm.GetFtab.SetValue(ycords,n,ynum)
   
   '-- Calculate the distance for the search point and the
   '-- centroid of the polygons and set that value in the distance field
   
    calnum = (((xnum - xcord)^2) + ((ynum - ycord)^2)).SqRt
    theThm.GetFtab.SetValue(Dist,n,calnum)
    n = n + 1
    end
   
   '-- End of Script  

   
   The script will:
   
   a. Prompt you to enter the zipcode ID.
   b. Initiate a search from the center of the target polygon.
   c. Create three fields to store information.
   d. Calculate the distance from the point entered and the centroids of the each polygon.
   e. Set the calculated value to the distance field.
3. Make view active, then compile and run the script.