matlab

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Using Autoplot in the MATLAB Environment

Audience: Autoplot users who would like to use the software to read data into MATLAB, and to use other Autoplot codes from these environments

Contents

  1. Introduction
  2. Getting Started
    1. Connecting the Jar File
      1. Connecting to MATLAB
    2. First Read of Data
    3. QDataSet in this Interface
  3. DataSet Properties
  4. The Rest of the Reader Interface
  5. Access other Autoplot classes
    1. Format datasets from MATLAB
    2. Static methods in Matlab
  6. Problems
  7. See Also
  8. Complete MATLAB Examples
  9. Previous Documentation

1. Introduction

Both IDL and MATLAB make it extremely easy to use Java code in these environments. Autoplot is able to read data from a variety of input sources using compact URIs to specify data locations, making it useful accessing digital data. For example, it's difficult to read data from an Excel worksheet into IDL, but since Autoplot can read this data, it becomes just as easy to read data from this source as it is a table of ASCII data. Further, Matlab can read data from CDF files, but its low-level CDF interface makes Autoplot attractive, because you can access data with just several lines of code. Last, Autoplot can automatically retrieve and manage data from remote sites via FTP and HTTP, so this mechanism can be used in IDL and MATLAB as well.

Autoplot contains a number of codes that are useful, in addition to reading data. For example, Autoplot is able to write data to a number of data formats, and this code is useful in Matlab as well.

2. Getting Started

First we need to connect the Autoplot code to the environment. In these examples, "Unix>" is used to indicate commands entered into a Unix BASH shell, and "MATLAB>" an MATLAB v7.7 session.

2.1. Connecting the Jar File

In either case, you'll need to download the Autoplot "single jar" release that is available along with each release of the software. For example, the development release at http://autoplot.org/jnlp/v2015a_11/ has a link to a single jar version here: http://autoplot.org/jnlp/v2015a_11/autoplot.jar. For MATLAB, you don't need to download the file, but to be consistent with IDL, we will download it to /tmp/autoplot.jar or some location appropriate for your workstation. This 25 megabyte jar file is similar to a .so file from C and Fortran, and contains compiled code and also needed resources. Note this is a full Autoplot and can be used from the command line, bypassing the mechanism normally used to launch Autoplot. If this seems large, consider that this contains code to read NetCDF, OpenDAP, CDF, Excel, and many other forms of data.

2.1.1. Connecting to MATLAB

MATLAB is able to add the jar after the session is started, with the command "javaaddpath":

MATLAB> javaaddpath( '/tmp/autoplot.jar' )

Note this can be a URL, like

MATLAB> javaaddpath( 'http://autoplot.org/jnlp/v2015a_5/autoplot.jar' )

Note older versions of Matlab use Java 6 and will not work with Autoplot version v2015a_5 and newer.

Now we can test to see that the jar file is connected:

MATLAB> apds  = org.virbo.idlsupport.APDataSet;
QDataSetBridge v1.8.01
APDataSet v1.3.2

2.2. First Read of Data

Autoplot can be used to read data into IDL and MATLAB
Autoplot can be used to read data into IDL and MATLAB

Suppose you have been using the Autoplot URI (data address) http://www.autoplot.org/data/swe-np.xls?column=data&depend0=dep0 to read data into Autoplot.

MATLAB> apds.setDataSetURI( 'http://www.autoplot.org/data/swe-np.xls?column=data&depend0=dep0' )
MATLAB> apds.doGetDataSet

Note there's a bug where MATLAB is unable to read AbstractPreferences, and you see an error message associated with this. This message can be ignored. Note the default autoplot_data/fscache must always be used.

MATLAB> apds
data: data[dep0=287] (dimensionless)
dep0: dep0[287] (t1970) (DEPEND_0)
MATLAB> plot( apds.values )

2.3. QDataSet in this Interface

This interface is meant to provide access to anything that can be represented within Autoplot and its internal data model, QDataSet.

QDataSet is meant to be a simple, uniform data interface that is adapted to many different syntaxes, including Java, Python, C, IDL and MATLAB. However, it's more of a guide than a specification, and since both IDL and MATLAB are slow when many commands are executed, we provide access to data via arrays rather than individual values as in Java. Also, we provide access to timetags and other independent data through the one object. This should simplify use in the environments. For example, instead of:

apds.property( QDataSet.DEPEND_0 ).values()

we say:

dep0Name= apds.depend(0)
x= apds.values( dep0Name )

or

x= apds.values( apds.depend(0) )

Another difference is that the apds is mutable, meaning its state can be changed, whereas QDataSets are generally immutable. For example, you can tell the apds what your preferred units are, affecting what is returned by the values() command.

3. DataSet Properties

You can access the dataset properties like so:

dsp= apds.properties( )
dsp.get('NAME')

yp= apds.properties( 'dep0' )
yp.get('UNITS') 

or

apds.property( 'dep0', 'UNITS' )

4. The Rest of the Reader Interface

What are the X values? They are in some strange unit that the data source chooses. In this example it is "t1970", which is the number of non-leap seconds since 1970-Jan-01T00:00. We can specify what units we want:

apds.setPreferredUnits( 'hours since 2007-01-17T00:00' )
plot( apds.values('dep0'), apds.values() ) 

(Problem: there's an inconsistency here between ooffice calc and what I'm getting. It almost looks like the autoplot xls export shifts to the local time. Use a different data source, like CDF.) Here are some example units strings: seconds since 2010-01-01T00:00, days since 2010-01-01T00:00, Hz, MHz. Note Autoplot's units are not fully developed, and conversions are not always possible.

We also can work with fill data:

apds.setFillValue( -999 )

This will convert whatever fill is in the dataset to this value. This saves the developer the time of reading what the fill, validmin, and validmax are in the QDataSet.

5. Access other Autoplot classes

Other classes Autoplot uses can be accessed. For example,

sc= org.virbo.autoplot.ScriptContext
x= sc.getCompletions( 'vap+cdfj:http://autoplot.org/data/somedata.cdf?')

lists all the variables in the CDF file.

5.1. Format datasets from MATLAB

Here's how we can use Autoplot's formatting to export data:

dsu= org.virbo.dataset.DataSetUtil
ds= dsu.asDataSet( randomu( s, 200 ) )    ; adapt IDL array to QDataSet.  TODO: What is Matlab code?
sc= org.virbo.autoplot.ScriptContext
sc.formatDataSet, ds, '/tmp/foo.xls'

The extension is used to control the output format.

5.2. Static methods in Matlab

Matlab> fs= org.das2.util.filesystem.FileSystem
Matlab> afs= fs.create('http://emfisis.physics.uiowa.edu/Flight/RBSP-B/L4/') 
Matlab> fsm= org.das2.fsm.FileStorageModel
Matlab> afsm= fsm.create(afs,'$Y/$m/$d/rbsp-b_WFR-waveform-magnitude_emfisis-L4_$Y$m$d_v$(v,sep).cdf')
Matlab> dru= org.das2.datum.DatumRangeUtil
Matlab> dr= dru.parseTimeRange('2014-02')
Matlab> ff= afsm.getFilesFor( dr )
Matlab> for i=0,n_elements(ff)-1 do print, ff[i].toString() # TODO what's the MATLAB?

6. Problems

There are some technical issues with all this.

Also:

  • It seems clear that you'd want to be able to use Autoplot to verify data, so applot should accept apds as an argument.
  • Filters are not readily accessible in IDL and MATLAB, and it would nice to show how these could be used.

7. See Also

Here is the nightly test which tells all: http://jfaden.net:8080/hudson/job/autoplot-test024/

8. Complete MATLAB Examples

apds= org.virbo.idlsupport.APDataSet;
t= '2011-01-17';
apds.setDataSetURI( strcat( 'http://cdaweb.gsfc.nasa.gov/sp_phys/data/ace/swepam/level_2_cdaweb/swe_k0/$Y/ac_k0_swe_$Y$m$d_v$v.cdf?Np&timerange=', t ) );
apds.doGetDataSet;
apds.setPreferredUnits( 'hours since 2011-01-17' );
plot( apds.values( apds.depend(0) ), apds.values );

Read Emfisis waveform files:

apds= org.virbo.idlsupport.APDataSet;
apds.setDataSetURI( 'http://emfisis.physics.uiowa.edu/Flight/RBSP-A/L2/2013/10/03/rbsp-a_WFR-waveform-continuous-burst_emfisis-L2_20131003T17_v1.3.2.cdf?BuSamples' );
apds.doGetDataSet;
apds.setPreferredUnits( 'seconds since 2013-10-03T17:00' );
plot( apds.values( apds.depend(1) ), apds.values[0,:] );

We wish to easily write Excel files (.xls). This script allows us to do this with Autoplot:

javaaddpath( 'http://autoplot.org/jnlp/latest/autoplot.jar' )
Ops = org.virbo.dsops.Ops;
Util= org.virbo.dataset.DataSetUtil;
SC= org.virbo.autoplot.ScriptContext; 

tt= Ops.labels( {  'experiment_1', 'experiment_2' } );
ll= Ops.labels( { 'ch1','ch2','ch3','ch4','ch5','ch6' } );
ds= rand(2,6);
ds= Util.asDataSet( ds );
ds= Ops.link( tt, ll, ds );
SC.formatDataSet( ds, '/tmp/mydata.xls?sheet=sh1' );

ds= rand(2,6);
ds= Util.asDataSet( ds );
ds= Ops.link( tt, ll, ds );
SC.formatDataSet( ds, '/tmp/mydata.xls?sheet=sh2&append=T' );

9. Previous Documentation

Retrieved from "http://autoplot.org//matlab"
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