WCS Handler

From OPeNDAP Documentation
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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.

URL Decomposition

Consider this URL: http://server:port/opendap/wcs/project/site/serviceName/coverage/date


Top Level Catalog

URL Pattern:

http://server:port/opendap/
http://server:port/opendap

Corresponds 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

WCS Project List

URL Pattern:

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

Corresponds 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


Project Site List

URL Pattern:

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


List of WCS servers

URL Pattern:

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

Correspond to the list of WCS Servers available for the project called project and the site called site..

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


Correspond to the list of WCS Servers available for the project called CEOP and the site called BER.. 

<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


Coverage List

URL Pattern:

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

Corresponds 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

Corresponds 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...

List of dates for which is data is available

URL Pattern:

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

Corresponds 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

Corresponds 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

Data Access URL's

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: 

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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