关于使用c#使用GADL处理矢量或者栅格数据的资料，大家随便都能找到很多，这里不做赘述。
现在需要处理如标题所述的gdal Can't load requested DLL的问题，今天遇到的问题详细为：
gdal Can't load requested DLL ogr_MSSQLSpatial.dll ，都知道使用GDAL要先初始化配置：
GdalConfiguration.ConfigureGdal();
GdalConfiguration.ConfigureOgr();初始化配置在添加GADL包后自动生成的GdalConfiguration.cs中：
/******************************************************************************
*
* Name: GdalConfiguration.cs.pp
* Project: GDAL CSharp Interface
* Purpose: A static configuration utility class to enable GDAL/OGR.
* Author: Felix Obermaier
*
******************************************************************************
* Copyright (c) 2012-2018, Felix Obermaier
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*****************************************************************************/
using System;
using System.Diagnostics;
using System.IO;
using System.Reflection;
using System.Runtime.InteropServices;
using Gdal = OSGeo.GDAL.Gdal;
using Ogr = OSGeo.OGR.Ogr;
namespace TifPipei
{
public static partial class GdalConfiguration
{
private static volatile bool _configuredOgr;
private static volatile bool _configuredGdal;
private static volatile bool _usable;
[DllImport("kernel32", CharSet = CharSet.Auto, SetLastError = true)]
static extern bool SetDefaultDllDirectories(uint directoryFlags);
// LOAD_LIBRARY_SEARCH_DEFAULT_DIRS
private const uint DllSearchFlags = 0x00001000;
[DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool AddDllDirectory(string lpPathName);
/// <summary>
/// Construction of Gdal/Ogr
/// </summary>
static GdalConfiguration()
{
string executingDirectory = null, gdalPath = null, nativePath = null;
try
{
if (!IsWindows)
{
const string notSet = "_Not_set_";
string tmp = Gdal.GetConfigOption("GDAL_DATA", notSet);
_usable = tmp != notSet;
return;
}
executingDirectory = AppContext.BaseDirectory;
if (string.IsNullOrEmpty(executingDirectory))
throw new InvalidOperationException("cannot get executing directory");
// modify search place and order
SetDefaultDllDirectories(DllSearchFlags);
gdalPath = Path.Combine(executingDirectory, "gdal");
nativePath = Path.Combine(gdalPath, GetPlatform());
if (!Directory.Exists(nativePath))
throw new DirectoryNotFoundException($"GDAL native directory not found at '{nativePath}'");
if (!File.Exists(Path.Combine(nativePath, "gdal_wrap.dll")))
throw new FileNotFoundException(
$"GDAL native wrapper file not found at '{Path.Combine(nativePath, "gdal_wrap.dll")}'");
// Add directories
AddDllDirectory(nativePath);
AddDllDirectory(Path.Combine(nativePath, "plugins"));
// Set the additional GDAL environment variables.
string gdalData = Path.Combine(gdalPath, "data");
Environment.SetEnvironmentVariable("GDAL_DATA", gdalData);
Gdal.SetConfigOption("GDAL_DATA", gdalData);
//string driverPath = Path.Combine(nativePath, "plugins");
Environment.SetEnvironmentVariable("GDAL_DRIVER_PATH", "./gdal/plugins");
OSGeo.OSR.Osr.SetPROJSearchPath("./gdal/plugins");
Environment.SetEnvironmentVariable("GEOTIFF_CSV", gdalData);
Gdal.SetConfigOption("GEOTIFF_CSV", gdalData);
//string projSharePath = Path.Combine(gdalPath, "share");
//Environment.SetEnvironmentVariable("PROJ_LIB", projSharePath);
//Gdal.SetConfigOption("PROJ_LIB", projSharePath);
//OSGeo.OSR.Osr.SetPROJSearchPaths(new[] { projSharePath });
Environment.SetEnvironmentVariable("PROJ_LIB", "./gdal/share");
OSGeo.OSR.Osr.SetPROJSearchPath("./gdal/share");
string certificateFile = Path.Combine(gdalPath, "curl-ca-bundle.crt");
Gdal.SetConfigOption("GDAL_CURL_CA_BUNDLE", certificateFile);
_usable = true;
}
catch (Exception e)
{
_usable = false;
Trace.WriteLine(e, "error");
Trace.WriteLine($"Executing directory: {executingDirectory}", "error");
Trace.WriteLine($"gdal directory: {gdalPath}", "error");
Trace.WriteLine($"native directory: {nativePath}", "error");
//throw;
}
}
/// <summary>
/// Gets a value indicating if the GDAL package is set up properly.
/// </summary>
public static bool Usable
{
get { return _usable; }
}
/// <summary>
/// Method to ensure the static constructor is being called.
/// </summary>
/// <remarks>Be sure to call this function before using Gdal/Ogr/Osr</remarks>
public static void ConfigureOgr()
{
if (!_usable) return;
if (_configuredOgr) return;
// Register drivers
Ogr.RegisterAll();
_configuredOgr = true;
PrintDriversOgr();
}
/// <summary>
/// Method to ensure the static constructor is being called.
/// </summary>
/// <remarks>Be sure to call this function before using Gdal/Ogr/Osr</remarks>
public static void ConfigureGdal()
{
if (!_usable) return;
if (_configuredGdal) return;
// Register drivers
Gdal.AllRegister();
_configuredGdal = true;
PrintDriversGdal();
}
/// <summary>
/// Function to determine which platform we're on
/// </summary>
private static string GetPlatform()
{
return Environment.Is64BitProcess ? "x64" : "x86";
}
/// <summary>
/// Gets a value indicating if we are on a windows platform
/// </summary>
private static bool IsWindows
{
get
{
var res = !(Environment.OSVersion.Platform == PlatformID.Unix ||
Environment.OSVersion.Platform == PlatformID.MacOSX);
return res;
}
}
private static void PrintDriversOgr()
{
#if DEBUG
if (_usable)
{
var num = Ogr.GetDriverCount();
for (var i = 0; i < num; i++)
{
var driver = Ogr.GetDriver(i);
Trace.WriteLine($"OGR {i}: {driver.GetName()}", "Debug");
}
}
#endif
}
private static void PrintDriversGdal()
{
#if DEBUG
if (_usable)
{
var num = Gdal.GetDriverCount();
for (var i = 0; i < num; i++)
{
var driver = Gdal.GetDriver(i);
Trace.WriteLine($"GDAL {i}: {driver.ShortName}-{driver.LongName}");
}
}
#endif
}
}
}以上错误提示：无法在xxx\plugins\目录下找到 ogr_MSSQLSpatial.dll ，那么在以上代码的设置plugins环境时是不是初始化无法定位到plugins目录呢？
测试：将原始代码中设置环境变量强制修改成plugins的目录
原始代码部分：
string driverPath = Path.Combine(nativePath, "plugins");
Environment.SetEnvironmentVariable("GDAL_DRIVER_PATH", driverPath);
Gdal.SetConfigOption("GDAL_DRIVER_PATH", driverPath);修改为：
Environment.SetEnvironmentVariable("GDAL_DRIVER_PATH", "./gdal/plugins");
OSGeo.OSR.Osr.SetPROJSearchPath("./gdal/plugins");惊喜出现了，错误消失，程序正常运行。
总结：GADL在C# 中使用着实经常出现问题，大家的问题五花八门，需要自己去追踪一下。