Can't get WebSite Project relative path from Sln file

I try to get WebSite Project Relative path from Sln file by using "Microsoft.Build.Construction.SolutionFile". But the relative path is wrong in "ProjectInSolution" type.

For example, this is Sln file, relative path is "http://localhost/WebSite" in "ProjectInSolutin" type, How Can I get "............\inetpub\wwwroot\WebSite\" from "ProjectInSolution"? Or is there any other type I can use?

```
Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 14

VisualStudioVersion = 14.0.25123.0
MinimumVisualStudioVersion = 10.0.40219.1
Project("{E24C65DC-7377-472B-9ABA-BC803B73C61A}") = "WebSite", "http://localhost/WebSite", "{0E90CBE5-EA94-41CD-8A64-8D5418B0B5D8}"
ProjectSection(WebsiteProperties) = preProject
UseIISExpress = "false"
TargetFrameworkMoniker = ".NETFramework,Version%3Dv4.5.1"
Debug.AspNetCompiler.VirtualPath = "/WebSite"
Debug.AspNetCompiler.PhysicalPath = "............\inetpub\wwwroot\WebSite\"
Debug.AspNetCompiler.TargetPath = "PrecompiledWeb\WebSite\"
Debug.AspNetCompiler.Updateable = "true"
Debug.AspNetCompiler.ForceOverwrite = "true"
Debug.AspNetCompiler.FixedNames = "false"
Debug.AspNetCompiler.Debug = "True"
Release.AspNetCompiler.VirtualPath = "/WebSite"
Release.AspNetCompiler.PhysicalPath = "............\inetpub\wwwroot\WebSite\"
Release.AspNetCompiler.TargetPath = "PrecompiledWeb\WebSite\"
Release.AspNetCompiler.Updateable = "true"
Release.AspNetCompiler.ForceOverwrite = "true"
Release.AspNetCompiler.FixedNames = "false"
Release.AspNetCompiler.Debug = "False"
SlnRelativePath = "............\inetpub\wwwroot\WebSite\"
DefaultWebSiteLanguage = "Visual C#"
EndProjectSection
EndProject
Global
GlobalSection(SolutionConfigurationPlatforms) = preSolution
Debug|Any CPU = Debug|Any CPU
EndGlobalSection
GlobalSection(ProjectConfigurationPlatforms) = postSolution
{0E90CBE5-EA94-41CD-8A64-8D5418B0B5D8}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
{0E90CBE5-EA94-41CD-8A64-8D5418B0B5D8}.Debug|Any CPU.Build.0 = Debug|Any CPU
EndGlobalSection
GlobalSection(SolutionProperties) = preSolution
HideSolutionNode = FALSE
EndGlobalSection
EndGlobal
```