LAS

LAS is an acronym for Live Access Server. It's an UI oriented to serve large datafiles. It uses OpenDAP. The MOHID uses LAS in order to distribute its datafiles to project partners or other endusers. The LAS official webpage is found at http://ferret.wrc.noaa.gov/Ferret/LAS/.

Quick start user's guide

From ncBrowse

Download and install the latest version of the Java platform from Sun.
Download and install the latest version of ncBrowse.
Run ncBrowse.
Go to file --> LAS and enter the URL http://data.mohid.com/las-bin/LASserver.pl.
Select the desired dataset.
Select a desired variable.
You can now browse the variable at will in ncBrowse.

From a web-browser

Open your favorite web-browser and write down http://data.mohid.com:8080/las/servlets/dataset.
Select a dataset.
Select variables then clik next.
Select a region with the interactive map, a time window and a ROI (or view).
Select the desired output. It can be in binary or ascii format, or it can be a color plot.
Click next and you should get in a few moments the results.

Note: the color plot is delivered on-the-fly by Ferret. It can be customized.

Developper's guide

This guide is intended to intranet users only.

How to login to data.mohid.com

Ssh data.mohid.com (guest:guest). Then enter as root (su root). You are now able to manage the LAS server. Windows users are recommended to use PuTTy .

How to initialize the tomcat server

Sometimes the tomcat server may be down even if you made a clean reboot. You have then to initialize it manually. To do so, perform the start command below.

start: /home/guillaume/public_html/las/startserver.pl
stop: /home/guillaume/public_html/las/stopserver.pl

Or you could initialize it from the http://data.mohid.com/las.xml page.

How to properly initialize the LAS

Make sure the prerequisites are met.
>./configure

The configure script will install a lot of perl modules. Should they fail, then install them manually. Use perl -MCPAN -e shell; install [module]; or yum [perl-mod-rpm-package].

Add the following lines to httpd.conf accordingly to your installation directory:

ScriptAlias  /las-bin/ /home/guillaume/public_html/las/server/
Alias /las-output/ /home/guillaume/public_html/las/server/output/

<Directory "/home/guillaume/public_html/las/server">
    AllowOverride None
    Options ExecCGI
    Order allow,deny
    Allow from all
</Directory>

Un/commented the following lines in httpd.conf (this step may be superfluous):

<IfModule mod_userdir.c>
    ...
    #UserDir disable
    ...
    UserDir public_html
    ...
</IfModule>

Restart httpd
Perform the following permissions in /home:

> sudo chown -R guillaume:apache guillaume
> sudo chmod -R 755 guillaume

Restart the las tomcat
Perform a simple test from /home/guillaume/public_html/las:

> ./bin/lasget.pl  -x -10:10 -y -30:-20 -z 0 -f txt -o salt.txt 
http://data.mohid.com/las-bin/LASserver.pl levitus_climatology_cdf salt

Whenever an httpd error occurs, check the log file:

> sudo tail -f /var/log/httpd/error_log

NOTE: typically, the issue comes down to permission problems: make sure the group of the full las path is the httpd group (apache) and make sure the full las path gets 755 permissions.

Can't create debug file log/debug (protection problem?) The CGI process that creates the plots needs permission to write in the las/server directory and a few of its sub-directories. The best way to do that is to give group ownership and group write permission to match the group that the Apache HTTPD process is running under. The following commands run in the $lasroot/ directory should do the trick, where "group" is the group as above.

> chgrp group server server/log server/output server/dods server/dods/.dods_cache
> chgrp group server/log/* server/output/* server/dods/.dods_cache/*
> chgrp group server/dods/.dodsrc
> chmod g+w server server/log server/output server/dods server/dods/.dods_cache
> chmod g+w server/log/* server/output/* server/dods/.dods_cache/*
> chmod g+w server/dods/.dodsrc

How to add datasets in LAS

Make sure that mohid.nc, the dataset to share, exists in /var/data/mohid.nc. Then perform the following operations:

> source /usr/local/ferret_paths
> cd $lasroot/server
> addXml.pl -n http://data.mohid.com/opendap/nph-dods/mohid.nc -x las.xml mohid

Change the las.xml file so it includes the mohid.xml

> touch las.xml
> make

That should do it!

However for purposes of operational models, such as Mercator-IST, you can simply actualize the LAS from the web page http://data.mohid.com/las.xml. Find and use the las.php script.

How to change the categories in LAS

Key files:

$lasroot/server/las.xml. This file contains the las configuration. The datasets xml files and the categories xml file are includes.
$lasroot/server/catex.xml. This file is the xml to include in las.xml that defines the categories.

Actions:

> source /usr/local/ferret_paths
> cd $lasroot/server
Edit the las.xml and catex.xml at will. See the LAS documentation.
> touch las.xml
> make
That's it. Go to http://data.mohid.com:8080/las/servlets/dataset to see if it worked. If errors appear then go to #2.

How to change options in the LAS ui

Key file:

$ lasroot/server/ui.xml. This file contains the user-interface configuration.
$ lasroot/server/options.xml. This file contains the user-interface options configuration.

Actions:

> source /usr/local/ferret_paths
> cd $lasroot/server
Edit the options.xml at will. See the LAS documentation.
> touch las.xml
> make
That's it. Go to http://data.mohid.com:8080/las/servlets/dataset to see if it worked. If errors appear then go to #2.

How to change Ferret default properties

Here's how to change the default value in the options ui for the ferret land_fill option (you can see this document). Edit the las.xml and add the properties tag

<lasdata>
  <properties>
       <ferret>
           <land_type>none</land_type>
       </ferret>
  <properties>
...

Where to find ferret scripts

LAS ferret scripts are to be found in

$ lasroot/las/server/jnls

How to add a banner in the LAS website

Edit the

$lasroot/las/las_servlet/jakarta/webapps/las/VM_global_library.vm

Here's an example:


  <!------  Begin of Banner ------>
      <form method="POST" name="search" action="search">
      <tr>
    <td valign="center" align="right" background="../images/Mohid_Logo_banner_small.gif">
               <a href="$req.getContextPath()-FDS/LAS/" target="_blank">OPeNDAP (FDS)</a> |
               <a  href="javascript:showInfo('THREDDS Catalog')"
                         onMouseOver="window.status='Click for help'; return true"
                         onMouseOut="window.status=''; return true"
                        >THREDDS</a> |
                <a href="index">Index</a> | Search: <input type="text" name="terms">
                <a href="" onMouseOver="status='Search';return true" onClick="return stuffForm('search','search')"><image border="0" src="../images/go.gif" alt="Go"></a>
        <input type="hidden" name="nexturl">
        </td>
      <td><img src="../images/no.gif" width="0" height="75"></td>
      </tr>
      </form>
  <!------    End of Banner ------>

Troubleshooting

Problem: The LAS server goes down (along with the tomcat/jakarta server) when the java option is disabled in the web-browser. In other working LASes, this error doesnt happens. The tomcat logs give

Gtk-WARNING **: cannot open display

Solution: Install the java virtual machine from sun, and activate the java option in the web-browsers. However this solution isn't entirely satisfactory.

Problem: When I restart the LAS from php and bash scripts I get javaclass exception errors.

Solution: There's a 90% chance that this is a permission error. Probably some critical file got owned by root and now your apache-owned scripts don't work. Here's how you can check it out: From the las root type:

> ll -R | grep root
> ll -R | grep maretec

No results should have returned. Otherwise if some root owned file returned, then you need to give them back to user apache of group apache:

> sudo chown -R apache:apache *

Now you can return to [1] and click on the reboot link and see if it worked.

Problem: The las.php script returns an error about one of the datasets when restarting and the LAS interface is down.

Solution: 40% of chance that the netcdf dataset file is invalid. Another 40% of chance that the netcdf dataset was invalid but was meanwhile replaced with by a valid dataset, and yet, the error still persists when las.php script is run. To solve the latter persistent problem, you need to remove the persistent LAS xml file corresponding to that dataset:

> cd /home/guillaume/public_html/las/server
> mv mercator200?????DomainProperty.xml mercator200?????DomainProperty.xml.bak

Then run the las.php again, and you should be fine.

External references

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