WCS Handler

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The current implementation of the WCS gateway is hosed. I started working on a new design.

I started working on a !WcsDispatchHandler and it made me start to think it might be much natural to make it a module for the BES. I think I can do it in the OLFS. In fact I am sure I can manage it.


Here's how it could work.

Consider this URL:

!http://server:port/opendap/wcs/project/site/serviceName/coverage/date

!http://server:port/opendap/


!http://server:port/opendap

Correspond to the top level catalog in the BES. Some how we need the show catalog for "/" command to return a dataset element for the wcs module (when it's installed) at the top level: {{{ <showCatalog> 

   <response>
       <dataset isData="false" thredds_collection="true">
           <name>/</name>
           <size>238</size>
           <lastmodified>
               <date>2008-02-18</date>
               
           </lastmodified>
           <count>1</count>
           <dataset isData="false" thredds_collection="true">
               <name>wcs</name>
               <size>000</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
       </dataset>
   </response>

</showCatalog> }}} Size=000

lastModified=request_time

!http://server:port/opendap/wcs/

!http://server:port/opendap/wcs

Correspond to the project list:

{{{ <showCatalog> 

   <response>
       <dataset isData="false" thredds_collection="true">
           <name>/wcs</name>
           <size>238</size>
           <lastmodified>
               <date>2008-02-18</date>
               
           </lastmodified>
           <count>2</count>
           <dataset isData="false" thredds_collection="true">
               <name>CEOP</name>
               <size>#ofSites</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
           <dataset isData="false" thredds_collection="true">
               <name>REAP</name>
               <size>ofSites</size>
               <lastmodified>
                   <date>Time</date>
                   
               </lastmodified>
           </dataset>
       </dataset>
   </response>

</showCatalog> }}} Size=#_of_sites in that project

lastModified=request_time


!http://server:port/opendap/wcs/project/

!http://server:port/opendap/wcs/project

Correspond to the site list for the project called project.

!http://server:port/opendap/wcs/CEOP/

!http://server:port/opendap/wcs/CEOP

Correspond to the site list for project called CEOP:

{{{ <showCatalog> 

   <response>
       <dataset isData="false" thredds_collection="true">
           <name>/wcs/CEOP</name>
           <size>238</size>
           <lastmodified>
               <date>2008-02-18</date>
               
           </lastmodified>
           <count>2</count>
           <dataset isData="false" thredds_collection="true">
               <name>BER</name>
               <size>000</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
           <dataset isData="false" thredds_collection="true">
               <name>BON</name>
               <size>000</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
       </dataset>
   </response>

</showCatalog> }}}

size=#_of_WCSService_elements in the config file

lastModified=request_time


!http://server:port/opendap/wcs/project/site/

!http://server:port/opendap/wcs/project/site

Correspond to the list of WCSServices.

!http://server:port/opendap/wcs/CEOP/BER/

!http://server:port/opendap/wcs/CEOP/BER

Correspond to the list of WCSServices.

{{{ <showCatalog> 

   <response>
       <dataset isData="false" thredds_collection="true">
           <name>/wcs/CEOP/BER/</name>
           <size>238</size>
           <lastmodified>
               <date>2008-02-18</date>
               
           </lastmodified>
           <count>2</count>
           <dataset isData="false" thredds_collection="true">
               <name>Server1</name>
               <size>000</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
           <dataset isData="false" thredds_collection="true">
               <name>Server2</name>
               <size>000</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
       </dataset>
   </response>

</showCatalog> }}}

size=#_of_<!CoverageSummary>_elements returned by a WCS !DescribeCoverage command to the server

lastModified=request_time


!http://server:port/opendap/wcs/project/site/wcs_service/

!http://server:port/opendap/wcs/project/site/wcs_service

Correspond to a list of the <!CoverageOffering> elements returned by the WCS server called wcs_service (as defined in a <!WCSService> element in the config file.) in response to the !DescribeCoverage command.


!http://server:port/opendap/wcs/CEOP/BER/Server1/

!http://server:port/opendap/wcs/CEOP/BER/Server1

Correspond to a list of the <!CoverageOffering> elements returned by the WCS server called Server1 (as defined in a <!WCSService> element in the config file.) in response to the !DescribeCoverage command. {{{ <showCatalog> 

   <response>
       <dataset isData="false" thredds_collection="true">
           <name>/wcs/CEOP/BER/Server1/</name>
           <size>238</size>
           <lastmodified>
               <date>2008-02-18</date>
               
           </lastmodified>
           <count>2</count>
           <dataset isData="false" thredds_collection="true">
               <name>TSurfAir</name>
               <size>000</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
           <dataset isData="false" thredds_collection="true">
               <name>GP_Surface</name>
               <size>000</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
       </dataset>
   </response>

</showCatalog> }}} size=# of items returned by !http://server:port/opendap/wcs/project/site/wcs_service/coverage/

lastModified=request_time

It is not unreasonable to think that we can make this response using an XSLT on the coverage description returned by the WCS server. In fact, in the OLFS we could build the directory page that way...

!http://server:port/opendap/wcs/project/site/wcs_service/coverage/

!http://server:port/opendap/wcs/project/site/wcs_service/coverage

Correspond to the intersection of the sets: 

* list of days that the coverage called coverage (From the <!CoverageOffering> element in the !DescribeCoverage response from the WCS server.)
* list of days that the coverage is requested by the site called site (From the <Site> element in the configuration coverage.)

!http://server:port/opendap/wcs/CEOP/BER/Server1/TSurfAir/

!http://server:port/opendap/wcs/CEOP/BER/Server1/TSurfAir

Correspond to the intersection of the sets:

  • list of days from the coverage called coverage TSurfAir.
  • list of days that the coverage is requested by the site called BER (From the <Site> element in the configuration coverage.)

{{{ <showCatalog> 

   <response>
       <dataset isData="false" thredds_collection="true">
           <name>/wcs/CEOP/BER/Server1/TSurfAir</name>
           <size>238</size>
           <lastmodified>
               <date>2008-02-18</date>
               
           </lastmodified>
           <count>2</count>
           <dataset isData="false" thredds_collection="false">
               <name>2002-10-01</name>
               <size>000</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
           <dataset isData="false" thredds_collection="false">
               <name>2004-09-30</name>
               <size>000</size>
               <lastmodified>
                   <date>Today</date>
                   
               </lastmodified>
           </dataset>
       </dataset>
   </response>

</showCatalog> }}}

size = Got me... maybe the age of the cached file if there is one already?

lastModified = request_time

At this point we are down to the data URLs.

From this path !http://server:port/opendap/wcs/project/site/wcs_service/coverage/date 

* DDS - !http://server:port/opendap/wcs/project/site/wcs_service/coverage/date.dds
* DAS - !http://server:port/opendap/wcs/project/site/wcs_service/coverage/date.das
* DDX - !http://server:port/opendap/wcs/project/site/wcs_service/coverage/date.ddx
* INFO - !http://server:port/opendap/wcs/project/site/wcs_service/coverage/date.info
* HTML - !http://server:port/opendap/wcs/project/site/wcs_service/coverage/date.html


From this path !http://server:port/opendap/wcs/CEOP/BER/Server1/TSurfAir/2008-02-18 

* DDS - !http://server:port/opendap/wcs/CEOP/BER/Server1/TSurfAir/2008-02-18.dds
* DAS - !http://server:port/opendap/wcs/CEOP/BER/Server1/TSurfAir/2008-02-18.das
* DDX - !http://server:port/opendap/wcs/CEOP/BER/Server1/TSurfAir/2008-02-18.ddx
* INFO - !http://server:port/opendap/wcs/CEOP/BER/Server1/TSurfAir/2008-02-18.info
* HTML !http://server:port/opendap/wcs/CEOP/BER/Server1/TSurfAir/2008-02-18.html

The WCS request needs to get this thing is:


{{{ http://g0dup05u.ecs.nasa.gov/cgi-bin/ceopAIRX2RET?service=WCS&version=1.0.0&request=GetCoverage&coverage=TSurfAir&crs=WGS84&bbox=-107.375000,51.625000,-102.625000,56.375000&format=netCDF&TIME=2002-08-31&resx=0.25&resy=0.25&interpolationMethod=Nearest%20neighbor" }}}

So let's pick that apart:

!http://g0dup05u.ecs.nasa.gov/cgi-bin/ceopAIRX2RET - Config file: <ServiceURL> element in <WCSService> (REQUIRED)

service=WCS - Config file: <service> element in <WCSService> (REQUIRED)

version=1.0.0 - Config file: <version> element in <WCSService> (REQUIRED)

request=!GetCoverage - The command that actually gets data. (REQUIRED)

coverage=TSurfAir - In the URL. (REQUIRED)

crs=WGS84 - Config file: <crs> element in <Site> Defines coordinates system for request and repsponse. (REQUIRED)

bbox=-107.375000,51.625000,-102.625000,56.375000 - Config file: <bbox> element in <Site> (REQUIRED)

format=netCDF - Config file: format element in <Site> (REQUIRED)

time=2002-08-31 - In the URL (REQUIRED)

resx=0.25 - Config file: <resx> element in <Site> (REQUIRED)

resy=0.25 - Config file: <resy> element in <Site> (REQUIRED)

interpolationMethod=Nearest%20neighbor - Config file: <interpolationMethod> element in <Site> (OPTIONAL)


Now, here's the beauty of it: WCS has a soap interface. Basically every one of these parameters appears as an element in the SOAP request document. The corresponding SOAP request for this URL is:

{{{ <GetCoverage version="1.0.0" service="WCS"> 

   <Coverage>TSurfAir</Coverage>
   <crs>WGS84</crs >
   <bbox>-107.475000,45.935000,-102.725000,50.685000</bbox>
   <format>netCDF</format>
   
   <resx>0.25</resx>
   <resy>0.25</resy>
   <interpolationMethod>Nearest neighbor</interpolationMethod>

</GetCoverage > }}}

It seems to me that the thing to do is to put all of these things in the configuration, and hold them to the same rules as the WCS folks. Then we can just grab and insert the Element objects when we are working in the code base. The formating of the content of the WCS request elements is the same as for the KVP encoding (HTTP URL), so for using the HTTP GET interface we still don't have to modify anything, just rearrange it.

The config file looks like this: {{{ <WCSConfig> 

   <WCSService name="server1" >
       <ServiceURL>
           http://g0dup05u.ecs.nasa.gov/cgi-bin/ceopAIRX2RET
       </ServiceURL>
       <service>WCS</service>
       <version>1.0.0</version>
   </WCSService>

   <WCSService name="server2" >
       <ServiceURL>
           http://g2dup05u.ecs.nasa.gov/cgi-bin/ceopAIRX2RET
       </ServiceURL>
       <service>WCS</service>
       <version>1.0.0</version>
   </WCSService>

   <Project name="CEOP">
       <Site name="BER">
           <label>BERMS Old Black Spruce</label>
           <WCSParameters>
               <bbox>-107.475000,45.935000,-102.725000,50.685000</bbox>
               
               <format>netCDF</format>
               <resx>0.25</resx>
               <resy>0.25</resy>
               <interpolationMethod>Nearest neighbor</interpolationMethod>
           </WCSParameters>
       </Site>
       <Site name="BON">
           <label>Bondville</label>
            <WCSParameters>
              <crs>WGS84</crs >
               <bbox>-90.665000,37.635000,-85.915000,42.385000</bbox>
               
               <format>netCDF</format>
               <resx>0.25</resx>
               <resy>0.25</resy>
               <interpolationMethod>Nearest neighbor</interpolationMethod>
           </WCSParameters>
       </Site>
   </Project>

</WCSConfig> }}}

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