public async Task<NexradScan> FetchNexradScanAsync(string site, string product, string filename)
{
// http://level3.allisonhouse.com/level3/f410ba3360389cc8401869160fc0a4cb/MPX/N0U/N0U_20140416_1641
// // http://weather.noaa.gov/pub/SL.us008001/DF.of/DC.radar/DS.p19r0/SI.kmpx/
// Normalize parameters
site = site.ToLowerInvariant();
product = product.ToLowerInvariant();
var scan = new NexradScan();
var key = String.Format("{0}/{1}/{2}", site, product, filename);
// Check cache and return scan if one is found
scan = cache.Get(key) as NexradScan;
if (scan != null)
return scan;
// No cached scan found, go grab a new one and decode it
var filelist = new List<string>();
var nexradbase = "http://weather.noaa.gov/pub/SL.us008001/DF.of/DC.radar/DS.{0}/SI.{1}/{2}";
switch (product)
{
case "n0r":
product = "p19r0";
break;
}
site = site.ToLowerInvariant();
var endpoint = String.Format(nexradbase, product, site, filename);
Stream response;
using (var client = new HttpClient())
{
response = await client.GetStreamAsync(endpoint);
}
if (response != null)
{
using (var ms = new MemoryStream())
{
response.CopyTo(ms);
scan = ParseNexrad(ms);
}
}
// Add scan to cache
policy.AbsoluteExpiration = DateTimeOffset.Now.AddMinutes(1);
cache.Add(key, scan, policy);
return scan;
}
public static NexradScan ParseNexrad(MemoryStream stream)
{
var nexrad = new NexradScan();
try
{
var headerData = new byte[30];
byte[] descriptorData;
var bytes = new byte[stream.Length];
descriptorData = new byte[stream.Length - 30];
var descriptor = new Descriptor();
var symbology = new Symbology();
// Header
stream.Position = 0;
stream.Read(headerData, 0, 30);
var headerString = System.Text.Encoding.UTF8.GetString(headerData);
headerString = headerString.Replace("\n", string.Empty).Replace("\r", " ").Replace(" ", " ");
var headerStrings = headerString.Split(' ');
var header = new Header { Code = headerStrings[0], Site = headerStrings[1], Date = headerStrings[2], FullProductCode = headerStrings[3] };
header.BodyCode = ReadHalfWord(stream);
header.BodyDate = ReadHalfWord(stream);
header.BodyTime = ReadWord(stream);
header.Length = ReadWord(stream);
header.SourceId = ReadHalfWord(stream);
header.DestinationId = ReadHalfWord(stream);
header.BlockCount = ReadHalfWord(stream);
// Descriptor
descriptor.Divider = ReadHalfWord(stream);
descriptor.Latitude = ReadWord(stream);
descriptor.Longitude = ReadWord(stream);
descriptor.Height = ReadHalfWord(stream);
descriptor.Code = ReadHalfWord(stream);
descriptor.Mode = ReadHalfWord(stream);
descriptor.VolumeCoveragePattern = ReadHalfWord(stream);
descriptor.SequenceNumber = ReadHalfWord(stream);
descriptor.ScanNumber = ReadHalfWord(stream);
descriptor.ScanDate = ReadHalfWord(stream);
descriptor.ScanTime = ReadWord(stream);
descriptor.GenerationDate = ReadHalfWord(stream);
descriptor.GenerationTime = ReadWord(stream);
descriptor.ProductSpecific1 = ReadHalfWord(stream);
descriptor.ProductSpecific2 = ReadHalfWord(stream);
descriptor.ElevationNumber = ReadHalfWord(stream);
descriptor.ProductSpecific3 = ReadHalfWord(stream);
descriptor.Threshold1 = ReadHalfWord(stream);
descriptor.Threshold2 = ReadHalfWord(stream);
descriptor.Threshold3 = ReadHalfWord(stream);
descriptor.Threshold4 = ReadHalfWord(stream);
descriptor.Threshold5 = ReadHalfWord(stream);
descriptor.Threshold6 = ReadHalfWord(stream);
descriptor.Threshold7 = ReadHalfWord(stream);
descriptor.Threshold8 = ReadHalfWord(stream);
descriptor.Threshold9 = ReadHalfWord(stream);
descriptor.Threshold10 = ReadHalfWord(stream);
descriptor.Threshold11 = ReadHalfWord(stream);
descriptor.Threshold12 = ReadHalfWord(stream);
descriptor.Threshold13 = ReadHalfWord(stream);
descriptor.Threshold14 = ReadHalfWord(stream);
descriptor.Threshold15 = ReadHalfWord(stream);
descriptor.Threshold16 = ReadHalfWord(stream);
descriptor.ProductSpecific4 = ReadHalfWord(stream);
descriptor.ProductSpecific5 = ReadHalfWord(stream);
descriptor.ProductSpecific6 = ReadHalfWord(stream);
descriptor.ProductSpecific7 = ReadHalfWord(stream);
descriptor.ProductSpecific8 = ReadHalfWord(stream);
descriptor.ProductSpecific9 = ReadHalfWord(stream);
descriptor.ProductSpecific10 = ReadHalfWord(stream);
descriptor.Version = ReadByte(stream);
descriptor.SpotBlank = ReadByte(stream);
descriptor.SymbologyOffset = ReadWord(stream);
descriptor.GraphicOffset = ReadWord(stream);
descriptor.TabularOffset = ReadWord(stream);
if (descriptor.SymbologyOffset != 0)
{
symbology.Divider = ReadHalfWord(stream);
symbology.BlockId = ReadHalfWord(stream);
symbology.Length = ReadWord(stream);
symbology.Layers = ReadHalfWord(stream);
symbology.LayerDivider = ReadHalfWord(stream);
symbology.DataLength = ReadWord(stream);
symbology.PacketCode = ReadHalfWord(stream);
symbology.IndexFirstRangeBin = ReadHalfWord(stream);
symbology.RangeBinCount = ReadHalfWord(stream); // dataHeader[1]
symbology.SweepCenterI = ReadHalfWord(stream); // dataHeader[2]
symbology.SweepCenterJ = ReadHalfWord(stream); // dataHeader[3]
symbology.ScaleFactor = ReadHalfWord(stream); // dataHeader[4]
symbology.RadialCount = ReadHalfWord(stream); // dataHeader[5]
symbology.RadialData = new List<Radial>();
var radialCount = symbology.RadialCount;
for (var i = 0; i < radialCount; i++)
{
var radial = new Radial();
radial.ColorValues = new List<Int32>();
radial.RleCount = ReadHalfWord(stream);
radial.StartAngle = ReadHalfWord(stream) / 10D;
radial.AngleDelta = ReadHalfWord(stream) / 10D;
for (var j = 0; j < radial.RleCount * 2; j++)
{
var values = DecodeRLES(stream, descriptor);
radial.ColorValues.AddRange(values);
}
symbology.RadialData.Add(radial);
}
}
nexrad = new NexradScan { Header = header, Descriptor = descriptor, Symbology = symbology };
}
catch (Exception ex)
{
Console.WriteLine("Generic error while parsing Nexrad data", ex.ToString());
}
return nexrad;
}