Finding maximum pixel value

Question

Hi all,

I am trying to search for maximum pixel value in a raster within a defined search buffer and also at each degree from the source point.

So basically, if the source point is x,y . Starting from x,y, I want it to search maximum pixel value in 0°, 2°, 4° etc. till it reaches the buffer extent,  and the coordinates where maximum value is found.

Right now I am doing that by looping it and going to each pixel, checking its pixel value, comparing it to last value and then assigning the maximum. The code works, but at snail's pace.

I tried using IRasterstatistics and also tried exploring skipfactorX and y... but can seem to work it out.

My current code is in vba..
and it goes something like :

For iRowCount = 0 To pRasterLayer.RowCount - 1
        For iColCount = 0 To pRasterLayer.ColumnCount - 1
            
            x = pRaster2.ToMapX(iColCount)
            y = pRaster2.ToMapY(iRowCount)

Xle = Xle + 1

arrX(Xle) = x
arrY(Xle) = y

Next  iColCount
Next iRowCount

-------------------------------------------------------------
for q = 0 to xle

for dangle = 0 to 359 step 2

ExtentX = 200 * Sin(rAngle)   ''200 is the search buffer distance. I am actually taking it from the user defined text box value
 ExtentY = 200 * Cos(rAngle)

ExtentX = arrX(q) + ExtentX
    ExtentY = arrY(q) + ExtentY

x2 = arrX(q)
 y2 = arrY(q)

do until x2 = extentx and y2 = extenty

---- look through each pixel (Ipixelblock)
 ---- compare
---- assign max

loop

next
next

Another limitation with this code is that I have used arrays.
For a large raster and fine resolution, the size of the arrays exceeds to the limit where it gives me

runtime error : out of memory.
So I am stuck with using coarse resolution raster.

Please help

Thanks,
Priyanka

PriyankaMehta · Answer

Thanks a lot again Brian,

The code looks neat to me. I am yet to test it though..
The reason I want to do it to determine the sky view factor. It is a value that determines how much sky is obstructed. The raster pixel values are nothing but the height of the buildings.

If i am standing in the midst of tall buildings the amount of sky i would see is the sky view factor. 
The first tallest building that comes in my sight is the one that would be taken into consideration (Reason for the first maximum pixel) If there are consecutive pixels of the same elevation, then they might just be the breadth of that building

It is calculated by a formula and the output from above code is one of the input of the formula.

It is an interesting thing to study. Usually done for temperature modeling

Thanks again,
Priyanka

BrianBottoms · Answer

I cleaned up the code a little - I didn't know how to sort a collection of objects on 2 properties where the first is sorted descending (raster value) and the second sorted ascending (position of first max found). It turned out to be a lot easier than I thought. I was able to drop the more awkward part of the code. So the code does the same as before - returns 180 objects with x, y, and raster value of first maximum occurrence along each even azimuth from a source point (why you would do this I don't know...)Structure PT
        Implements IComparable
        Public X As Double
        Public Y As Double
        Public Degree As Integer
        Public Value As Double
        Public Position As Integer 'numeric order of point from center.

Public Function CompareTo(ByVal obj As Object) As Integer Implements System.IComparable.CompareTo
            Dim tmpObj As PT = CType(obj, PT)
            If Me.Value.CompareTo(tmpObj.Value) = 0 Then
                Return (Me.Position.CompareTo(tmpObj.Position))
            Else
                Return (tmpObj.Value.CompareTo(Me.Value))
            End If
        End Function
    End Structure
Private Function MaxPoints(ByVal BufferRadius As Double, ByVal Interval As Integer, ByVal InPoint As IPoint, ByVal pRaster2 As IRaster2) As ArrayList
        Dim al As New ArrayList
        Dim finalAl As New ArrayList
        Dim col As Integer
        Dim row As Integer
        Dim newPT As PT
        Dim z As Integer = 0
        Dim xCoord As Double
        Dim yCoord As Double
        Dim count As Integer

For x As Integer = 2 To 360 Step 2
            Do While z < BufferRadius
                xCoord = z * Math.Cos((90 - x) * Math.PI / 180.0F) + InPoint.X
                yCoord = z * Math.Sin((90 - x) * Math.PI / 180.0F) + InPoint.Y
                col = pRaster.ToPixelColumn(xCoord)
                row = pRaster.ToPixelRow(yCoord)
                newPT.Degree = x
                newPT.X = xCoord
                newPT.Y = yCoord
                newPT.Value = CDbl(pRaster.GetPixelValue(0, col, row))
                al.Add(newPT)
                z += Interval
                count += 1
            Loop
            al.Sort()
            finalAl.Add(al(0))
            al.Clear()
            z = 0
            count = 0
        Next

Return finalAl
    End Function

Brian

PriyankaMehta · Answer

Hey thanks again Brian,

I ll try the code and respond asap.

Thanks a lot again !!
Regards,
Priyanka