scanning an array

[Claus Mygind]

I have two arrays each contains two columns. lon and lat.

I want to use the lon and lat values from the one array to look and find the nearest matching values in the 2nd array.

Here is some sample data of longitude and latitude.

lat="39.7553670 " lon="-88.8309830"
lat="39.7874000 " lon="-89.1040170"
lat="39.8309670 " lon="-89.0850330"
lat="40.1745330 " lon="-88.2416830"

I will never have exact matching values, so I just want to find the best fit. The best fit in the 2nd array may be either a slightly higher or lower value than the search value.

I want to extract a value from a third column from the 2nd array and place it into a similar column of the first array.

Any suggestions on how that might be coded?

      aFoundCache = new Array(1,4)
      aFoundCache[1,1] = "WayPoint"
	aFoundCache[1,2] = "Lat"
	aFoundCache[1,1] = "Lon"
  	aFoundCache[1,1] = "Time"

      aTrackPoint = new Array(1,4)
      aTrackPoint[1,1] = "Lat"
      aTrackPoint[1,2] = "Lon"
      aTrackPoint[1,3] = "Date"
      aTrackPoint[1,4] = "Time"

[Dormilich]

how exactly are the lon/lat arrays defined?

// pseudo code
// using x, y as search values
// using lon, lat as reference values

// using least squares
for_each (// reference array) {
  stddev.push((lon - x)*(lon-x)+(lat-y)*(lat-y))
}

// find smallest value
for_each (// stddev) {
  if (stddev[i]<stddev[i-1])
    var min = i;
}

// et voilà, reference[min] is your closest match

[Claus Mygind]

Actually I made a mistake. The code I am using here is in my server side app. But the fundamentals you describe should work just the same. So I should be able to apply your excellent code. Thank very much.

[Dormilich]

your server side app may have a method to find the smallest value easier (something like e.g. min() …)

[Claus Mygind]

Nope what you provided was exactly what I needed.I would have had to write to disk in a table. I thank you very much. I was familiar with the formular so it was very easy to implement. You saved me a bunch of time.

I was even able to add a sort to put the points in proper order

If you like here is my server sided code which I derived from your example.

   //Add time stamp of time found to cache  from nearest track point
         //start at row 2 because row 1 is a header
         for nE = 2 to ALEN( aFoundCache,1 )


            aStd = new Array(1,2)
            aStd[1,1] = "Std Val"
            aStd[1,2] = "Time"

            x = aFoundCache[nE,2]
            y = aFoundCache[nE,3]

            //start at row 2 because row 1 is a header
            for nT = 2 to ALEN( aTrackPoint,1 )
               lat = aTrackPoint[nT,1]
               lon = aTrackPoint[nT,2]
               tim = aTrackPoint[nT,4]

               
               aStd.grow(1)
               aStd[ALEN( aStd,1 ),1] = (lon - x)*(lon-x)+(lat-y)*(lat-y)
               aStd[ALEN( aStd,1 ),2] = tim

            endfor

            //start at the 2nd row, first row is a header
            min = aStd[2,1]

            for nS = 2 to ALEN( aStd,1 )
               // find smallest value
               min = iif(aStd[nS,1] < min, aStd[nS,1], min  )
            endfor

            cRow = aStd.subscript(aStd.scan(min),1)
            aFoundCache[nE,4] = aStd[cRow,2]

         endfor

         aFoundCache.sort(4)