type
  TMyTerrainAlgorithm = class(TRandomTerrainAlgorithm)
    protected
      procedure Generate();
    public
      function GetHeightMap() : TBitmap; override;    
  end;  
  
{ TMyTerrainAlgorithm }


procedure TMyTerrainAlgorithm.Generate();
var x, z: Integer;
       i : Integer;
begin
  System.SetLength(FData, 256);
  for i := 0 to High(FData) do
    System.SetLength(FData[i], 256);
    
  for x := 0 to 255 do
    for z := 0 to 255 do
    begin
      FData[x, z] := Random(100) / 100;
    end;
end;

function TMyTerrainAlgorithm.GetHeightMap() : TBitmap;
begin
  Generate();

  result := inherited;
end;
			
LMyTerrainAlgorithm := TMyTerrainAlgorithm.Create();
try
  FTerrain.RandomTerrain(LMyTerrainAlgorithm);
finally
  FreeAndNil(LMyTerrainAlgorithm);
end;