/// <summary>
/// Tries to use the DEM stored in memory.
/// </summary>
/// <returns>NULL if the in-memory DEM is not available.</returns>
private RasterDigitalElevationModelBase TryMemory()
{
RasterDigitalElevationModelBase result = null;
long maxBytes = 1024 * 1024 * 1024 * 2L; // 2 GiB
// 2 GiB is the .NET limit for allocating RAM, at least in 2.0.
// See https://stackoverflow.com/questions/1087982/single-objects-still-limited-to-2-gb-in-size-in-clr-4-0
if (RequiredBytes > maxBytes)
{
this.ActivityLogger.LogFormat(ActivityLogLevel.Warning,
"In-memory cache not available due to DEM size of {0} MiB bigger than 2 GiB.", RequiredMebibytes);
return(null);
}
try
{
result = new MemoryBasedRasterDigitalElevationModel(
lonResolution, latResolution, lonOffset, latOffset, lonLength, latLength);
}
catch (OverflowException)
{
return(null);
}
catch (OutOfMemoryException)
{
this.ActivityLogger.LogFormat(ActivityLogLevel.Warning,
"In-memory cache not available due to not enough free memory. DEM needs {0} MiB.", RequiredMebibytes);
return(null);
}
return(result);
}
/// <summary>
/// Returns a suitable DEM storage which is supported by the executing system.
/// </summary>
/// <returns>NULL if no model is available.</returns>
public RasterDigitalElevationModelBase CreateSupportedModel()
{
RasterDigitalElevationModelBase result = null;
// First of all try to save the DEM in memory
result = TryMemory();
// If this fails try the filesystem
if (result == null)
{
result = TryFilesystem();
}
if (result is FileBasedRasterDigitalElevationModel)
{
string msg = "Using the filesystem as cache. This will take a huge amount of time, be patient.";
msg += " It will also create a {0} MiB file in your location for temporary files.";
this.ActivityLogger.LogFormat(ActivityLogLevel.Warning, msg, RequiredMebibytes);
}
return(result);
}
public IDigitalElevationModel LoadDemForArea(Bounds2 bounds)
{
// make sure the cache directory exists
if (false == Directory.Exists(srtm3CachePath))
{
Directory.CreateDirectory(srtm3CachePath);
}
// first create a list of geographicals cells which constitute the specified area
IDictionary <int, Srtm3Cell> cellsToUse = new Dictionary <int, Srtm3Cell> ();
for (int lat = CalculateCellDegrees(bounds.MinY); lat <= CalculateCellDegrees(bounds.MaxY); lat++)
{
for (int lng = CalculateCellDegrees(bounds.MinX); lng <= CalculateCellDegrees(bounds.MaxX); lng++)
{
Srtm3Cell cell = new Srtm3Cell((Int16)lng, (Int16)lat);
cellsToUse.Add(Srtm3Cell.CalculateCellKey(cell), cell);
}
}
// then fetch a list of already downloaded cells
IDictionary <int, Srtm3Cell> cachedCells = FetchCachedCellsList();
try
{
foreach (Srtm3Cell cell in cellsToUse.Values)
{
// if it is not cached...
if (false == cachedCells.ContainsKey(Srtm3Cell.CalculateCellKey(cell)))
{
// find the right subdirectory
SrtmContinentalRegion continentalRegion = (SrtmContinentalRegion)index.GetValueForCell(cell.CellLon, cell.CellLat);
if (continentalRegion == SrtmContinentalRegion.None)
{
// the cell does not exist in the index, it is probably an ocean cell
// add an empty cell to the cache and go to the next cell
cachedCells.Add(Srtm3Cell.CalculateCellKey(cell), cell);
continue;
}
string filename = string.Format(System.Globalization.CultureInfo.InvariantCulture, "{0}.zip", cell.CellFileName);
string url = srtmSource + continentalRegion.ToString() + "/" + filename;
string localFilename = Path.Combine(srtm3CachePath, filename);
this.activityLogger.Log(ActivityLogLevel.Verbose, "Downloading SRTM cell " + cell.CellFileName);
WebRequest request = WebRequest.Create(new System.Uri(url));
WebResponse response = request.GetResponse();
// Get the stream containing content returned by the server.
Stream dataStream = response.GetResponseStream();
FileStream fileStream = new FileStream(localFilename, FileMode.OpenOrCreate);
//Download in chuncks
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = dataStream.Read(buffer, 0, buffer.Length)) > 0)
{
fileStream.Write(buffer, 0, bytesRead);
}
long receivedLength = fileStream.Length;
fileStream.Close();
dataStream.Close();
response.Close();
// Check if the download is complete.
if (response.ContentLength != -1 && response.ContentLength > receivedLength)
{
File.Delete(localFilename);
throw new WebException("Download incomplete (content length mismatch).", null, WebExceptionStatus.ReceiveFailure, response);
}
// unzip it and delete the zip file
FastZip zip = new FastZip();
zip.ExtractZip(localFilename, srtm3CachePath, null);
File.Delete(localFilename);
}
// now load it
cell.LoadFromCache(srtm3CachePath);
}
}
finally
{
}
// create elevation data
int west, south, east, north;
west = Srtm3Storage.CalculateCellPosition(bounds.MinX);
south = Srtm3Storage.CalculateCellPosition(bounds.MinY);
east = Srtm3Storage.CalculateCellPosition(bounds.MaxX);
north = Srtm3Storage.CalculateCellPosition(bounds.MaxY);
int width = east - west + 1;
int height = north - south + 1;
long requiredBytes = width * height * 2L;
int loadCounter = 1;
RasterDigitalElevationModelFactory factory = new RasterDigitalElevationModelFactory(1200, 1200, west, south, width, height);
factory.ActivityLogger = activityLogger;
RasterDigitalElevationModelBase dem = factory.CreateSupportedModel();
if (dem == null)
{
throw new PlatformNotSupportedException("No suitable location for the DEM found.");
}
// and fill the DEM with each cell points
foreach (Srtm3Cell cell in cellsToUse.Values)
{
this.activityLogger.LogFormat(ActivityLogLevel.Normal,
"Loading cell {0} of {1} into DEM", loadCounter++, cellsToUse.Values.Count);
dem.CopyElevationPointsFrom(cell);
}
return(dem);
}