Thursday, September 22, 2016

Export/Imoprt PostgreSQL database with PostGIS extension

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#Run from windows command prompt
#Create dump into dump.sql

C:\Program Files\PostgreSQL\9.4\bin>pg_dump.exe -h localhost -p 5432 -U username dbnameToExport > D:\dump.sql

#Import dump

C:\Program Files\PostgreSQL\9.4\bin>psql.exe -h localhost -p 5432 -U postgres dbnameToImport < D:/dump.sql

Password for user postgres:

Only super user can create PostGIS extension in PostgreSQL.

Reproject Geometry from WGS84 to Web Mercator Aux

ALTER TABLE table_name
            ALTER COLUMN column_name TYPE geometry(MultiPolygon, 3857) USING                        ST_Transform(ST_SetSRID(column_name,4326),3857) ;

Thursday, September 8, 2016

Solution: Vagrant stopped working - `open': Access is denied. (5) (ChildProcess::Error)

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ERROR from CMD with out running vagrant up as administrator

There was an error while executing `VBoxManage`, a CLI used by Vagrant
for controlling VirtualBox. The command and stderr is shown below.

Command: ["showvminfo", "18021ea0-83ee-43c3-9adb-26ad7eb0c6ca"]

Stderr: VBoxManage.exe: error: Failed to create the VirtualBox object!
VBoxManage.exe: error: Code CO_E_SERVER_EXEC_FAILURE (0x80080005) - Server execu
tion failed (extended info not available)
VBoxManage.exe: error: Most likely, the VirtualBox COM server is not running or
failed to start.

Error on running vagrant up as administrator from CMD

C:/HashiCorp/Vagrant/embedded/gems/gems/childprocess-0.5.9/lib/childprocess/wind
ows/handle.rb:12:in `open': Access is denied. (5) (ChildProcess::Error)
        from C:/HashiCorp/Vagrant/embedded/gems/gems/childprocess-0.5.9/lib/chil
dprocess/windows/process.rb:70:in `launch_process'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/childprocess-0.5.9/lib/chil
dprocess/abstract_process.rb:82:in `start'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/u
til/subprocess.rb:122:in `block in execute'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/u
til/safe_chdir.rb:26:in `block (2 levels) in safe_chdir'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/u
til/safe_chdir.rb:25:in `chdir'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/u
til/safe_chdir.rb:25:in `block in safe_chdir'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/u
til/safe_chdir.rb:24:in `synchronize'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/u
til/safe_chdir.rb:24:in `safe_chdir'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/u
til/subprocess.rb:121:in `execute'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/u
til/subprocess.rb:22:in `execute'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/u
til/platform.rb:129:in `cygwin_windows_path'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/plugins/provi
ders/virtualbox/driver/base.rb:50:in `block in initialize'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/plugins/provi
ders/virtualbox/driver/base.rb:42:in `each'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/plugins/provi
ders/virtualbox/driver/base.rb:42:in `initialize'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/plugins/provi
ders/virtualbox/driver/meta.rb:36:in `initialize'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/plugins/provi
ders/virtualbox/provider.rb:20:in `new'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/plugins/provi
ders/virtualbox/provider.rb:20:in `usable?'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/v
agrantfile.rb:138:in `machine_config'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/v
agrantfile.rb:45:in `machine'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/e
nvironment.rb:663:in `machine'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/p
lugin/v2/command.rb:177:in `block in with_target_vms'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/p
lugin/v2/command.rb:201:in `call'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/p
lugin/v2/command.rb:201:in `block in with_target_vms'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/p
lugin/v2/command.rb:183:in `each'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/p
lugin/v2/command.rb:183:in `with_target_vms'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/plugins/comma
nds/up/command.rb:131:in `install_providers'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/plugins/comma
nds/up/command.rb:85:in `execute'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/c
li.rb:42:in `execute'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/lib/vagrant/e
nvironment.rb:302:in `cli'
        from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.8.5/bin/vagrant:1
74:in `<main>'

Similar issue on Question from Stack Overflow

Fix steps for my machine-

1. Installed fresh - Vagrant (1.8.5)
2. Installed fresh Virtual box VirtualBox 5.1.4 for Windows host x86/amd64 - Version 5.1.4 r110228 (Qt5.5.1) 
3. Install Git bash version 2.8.2.windows.1 (64 bit)
4. Running Git bash as admin and calling vagrant up through that elevated console

Solution-
https://laracasts.com/discuss/channels/servers/vagrant-up-failing-trying-to-add-to-hosts



Friday, August 19, 2016

Code snippet: Open Folder Browser Dialog in WPF

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Install WPFFolderBrowser 1.0.2 from nuget gallery to use the Windows Vista / Windows 7 Folder Browser Dialog from your WPF projects, without any additional dependencies.

Install-Package WPFFolderBrowser
then import WPFFolderBrowser

using WPFFolderBrowser;
private void BrowseFolder()
        {
            WPFFolderBrowserDialog dd = new WPFFolderBrowserDialog();
            var result = dd.ShowDialog();
            if (result.HasValue)
            {
                TxtFvsAccessDbPath = dd.FileName;
            }
        }

Code snippet: WPF ListView SelectionChanged Event Handling in ViewModel

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Solution from Dhaval Patel in Sliverlight application works perfectly on my WPF application. I prefer his idea because it is more clear and cleaner than other solutions that  I have came with. The event handling approach explained as -"This is the way where You can Reach the Selection changed events in Your MVVM Application First Of all i tell you that Command Property only work in Button now we have to Explicitly binding that property in our Selection Changed event like List box or combo box in Your XMAL file"
<ListBox Name="MyListBox" ItemsSource="{Binding ListItems}" Height="150" Width="150" Margin="281,32,-31,118">

        <Local:Interaction.Triggers>
            <Local:EventTrigger EventName="SelectionChanged">
                <Local:InvokeCommandAction Command="{Binding MyCommand}" CommandParameter="{Binding ElementName=MyListBox,Path=SelectedItem}"/>
            </Local:EventTrigger>
        </Local:Interaction.Triggers>
    </ListBox>
for this you have to add dll Syatem.Windows.Interactivity now u have to add references in your xaml file namespace like
 xmlns:Local="clr-namespace:System.Windows.Interactivityassembly=System.Windows.Interactivity"

Thursday, August 18, 2016

Code snippet: Data binding between ViewModel and Radio Button in WPF

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Following example shows the data binding between radio buttons and ViewModel in WPF.

Parts of View.xaml

<Grid.Resources>
    <Utilities:RadioHelper x:Key="RadioConverter" />
    <Utilities:RadioHelper x:Key="InverseRadioConverter" Inverse="True" />
</Grid.Resources>
<RadioButton Name="radFvsOracle" GroupName="fvsStorage" Content="Oracle" Margin="7,0,0,0" IsChecked="{Binding Path=RadFvsResults, Converter= {StaticResource ResourceKey=RadioConverter}}"></RadioButton>
<RadioButton Name="radFvsAccess" GroupName="fvsStorage" Content="Access" Grid.Column="2" Margin="11,0,0,0" IsChecked="{Binding Path=RadFvsResults, Converter= {StaticResource ResourceKey=InverseRadioConverter}}"></RadioButton>

Parts of RadioHelper.cs

public class RadioHelper:IValueConverter 
    {
        public bool Inverse { get; set; }
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value != null)
            {
                bool boolValue = (bool)value;
                return this.Inverse ? !boolValue : boolValue;
            }
            return Binding.DoNothing;
       }
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            bool boolValue = (bool)value;
            if (!boolValue)
            {
                    return Binding.DoNothing;
            }
            return !this.Inverse;
        }
    }

Friday, August 12, 2016

Random Forest Regression, Negative Variance Explained mechanism

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Jeffery Evans, Senior Landscape Ecologist, The Nature Conservancy, Global Lands Science Team, Affiliate Assistant Professor, Zoology & Physiology, University of Wyoming explains a negative percent variance explained in a random forest regression in hilarious way -

I have recently been asked the question: “why do I receive a negative percent variance explained in a random forest regression”. Besides the obvious answer “because your model is crap” I thought that I would explain the mechanism at work here so the assumption is not that randomForests is producing erroneous results. For poorly supported models it is, in fact, possible to receive a negative percent variance explained.

Generally, explained variance (R²) is defined as:

R² = 1 - sum((ลท-mean(y))²) / sum((mean(y)-y)²)

However, as indicated by Breiman (2001) and the R randomForest documentation the (regression only) “pseudo R-squared” is derived as:

R² = 1 – (mean squared error) / var(y)

Which, mathematically can produce negative values. A simple interpretation of a negative R² (rsq), is that you are better off predicting any given sample as equal to overall estimated mean, indicating very poor model performance. 
 

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