Thursday, March 12, 2009

OpenGIS With .Net 2.0 And WCF

@YaronNaveh

Geospatial and location based services became very popular these days. One concern for developers of such applications is how to represent the data in the system. This includes simple data types such as points or coordinate systems and complex ones such as advanced topologies. The correct approach is of course to use types from the standard schema set of the Open Geospatial Consortium (OGC).

For a .Net developer this may imply the following needs:

  • Use xsd.exe to generate classes for serizliation

  • Create .Net 2.0 / WCF web services that utilize these schemas

  • Consume Wsdl's with these schemas


  • Unfortunetely the OpenGIS standard schemas are not interoperable with .Net. This has already been noticed by developers for older OpenGIS versions but newer versions seem to be equality incompatible.

    If you only want the fix without the details download it here and see in the end of the post the fix details:



    Here are some of the errors one gets when trying to consume Gml 3.1.1 and Gml 3.2.1 schemas in .Net:

    Gml 3.1.1 - WCF

    While using "add service reference" we get this error:


    Custom tool error: Failed to generate code for the service reference 'ServiceReference1'. Please check other error and warning messages for details.


    And after this an empty proxy code is generated:


    namespace ConsoleApplication1.ServiceReference1 {

    }



    Gml 3.1.1 - .Net 2.0

    The wsdl importing stage seems to work fine. Let's build a one line client:


    WebReference.Service c = new WebReference.Service();



    Such a simple client - what can possibly go wrong? Well nothing, except this:


    "There was an error reflecting property '_ReferenceSystem'."

    "There was an error reflecting type 'ConsoleApplication1.WebReference.AbstractReferenceSystemType'."
    ...

    "There was an error reflecting property 'Item'."
    ...
    "There was an error reflecting property 'Text'."

    "Member 'Text' cannot be encoded using the XmlText attribute. You may use the XmlText attribute to encode primitives, enumerations, arrays of strings, or arrays of XmlNode."


    And this is after I have omitted some inner exceptions.

    In some cases (depending on .Net 2.0 patch level) the below exception will appear - not much improvement:


    Unable to generate a temporary class (result=1).
    error CS0029: Cannot implicitly convert type 'ConsoleApplication70.localhost.LineStringSegmentType' to 'ConsoleApplication70.localhost.LineStringSegmentType[]'
    error CS0029: Cannot implicitly convert type 'ConsoleApplication70.localhost.LineStringSegmentType' to 'ConsoleApplication70.localhost.LineStringSegmentType[]'


    Finally, depending in the types we reference, we might get this one as well:


    There was an error reflecting type 'ConsoleApplication70.localhost.TopoSurfacePropertyType'.


    Gml 3.2.1 - WCF

    Proxy is generated but the simplest client throws this exception chain:


    There was an error reflecting type 'ConsoleApplication1.ServiceReference1.RingPropertyType'.

    "There was an error reflecting type 'ConsoleApplication1.ServiceReference1.RingType'."

    ...

    "Member 'Text' cannot be encoded using the XmlText attribute. You may use the XmlText attribute to encode primitives, enumerations, arrays of strings, or arrays of XmlNode."



    Gml 3.2.1 - .Net 2.0

    Guess what?


    "There was an error reflecting property '_ReferenceSystem'."

    "There was an error reflecting type 'ConsoleApplication1.WebReference.AbstractReferenceSystemType'."

    ...

    "Member 'Text' cannot be encoded using the XmlText attribute. You may use the XmlText attribute to encode primitives, enumerations, arrays of strings, or arrays of XmlNode."


    Why these errors happen?

    The errors appear in run-time when we instantiate the client proxy or web service. At this stage .Net creates the serialization assembly for each type and fails to do it for the proxy. Actually if we have marked the "generate serialization assembly" build option we could already see these errors in compile time.

    Now what?

    We need to fix the schemas or the proxy in order to make them interoperable with .Net. The fix must be compatible with the original schema, so it may change the schema syntax but must result in an isomorphic schema.

    Making Gml 3.2.1 work

    There are two reasons for this schema incomparability:

  • Cyclic schema references


  • From gml.xsd:


    <include schemaLocation="deprecatedTypes.xsd"/>


    From deprecatedTypes.xsd:


    <include schemaLocation="gml.xsd"/>


    One way to solve this is to remove deprecatedTypes.xsd altogether - it is not really required. We'll be nicer and just replace inside it the reference to gml.xsd with these direct references:


    <include schemaLocation="dynamicFeature.xsd"/>
    <include schemaLocation="topology.xsd"/>
    <include schemaLocation="coverage.xsd"/>
    <include schemaLocation="coordinateReferenceSystems.xsd"/>
    <include schemaLocation="observation.xsd"/>
    <include schemaLocation="temporalReferenceSystems.xsd"/>


  • Non-string lists

  • .Net does not support the xsd:list data type. When the list is of strings it works anyway since unresolved types are treated as strings. But for other types it is not supported. MSDN contains some more information on xsd:list support in .Net.

    basicTypes.xsd contains this:


    <simpleType name="doubleList">
       <annotation>
         <documentation>XML List based on XML Schema double type. An element of this type contains a space-separated list of double values</documentation>
       </annotation>
       <list itemType="double" />
    </simpleType>


    Which becomes this in the .Net proxy:


    ///
    [System.Xml.Serialization.XmlTextAttribute()]
    public double[] Value {
      get {
        return this.valueField;
      }
      set {
        this.valueField = value;
      }
    }


    which causes a run-time error since the XmlTextAttribute is only appropriate on strings.

    The solutions is to replace all non-string lists in the schema to strings so the above becomes:


    ...
    <list itemType="string" />
    ...


    And after this Gml 3.2.1 classes are serializable by .Net!


    Making Gml 3.1.1 work

    This version has two issues:

  • Same issue with lists as in 3.2.1 - same fix

  • I've seen this one a couple of times. Basically when there is a multidimensional array of a type which has a single child element in some cases .Net code generation is incorrect. Don't ask, long story... Just replace in geometryPrimitives.xsd:



  • <complexType name="LineStringSegmentArrayPropertyType">
      <sequence>
        <element ref="gml:LineStringSegment" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
    </complexType>


    With:


    <complexType name="LineStringSegmentArrayPropertyType">
      <sequence>
        <element ref="gml:LineStringSegment" minOccurs="0" maxOccurs="unbounded"/>
        <any />
      </sequence>
    </complexType>


    And we have 3.1.1 working as well!

    Download fix

    I have uploaded the fixed schemas to save your time:



    After you extract the zip the fixed schemas are in the below folders:


    opengis_net_fixed\gml\3.1.1_fixed
    opengis_net_fixed\gml\3.2.1_fixed

    @YaronNaveh

    What's next? get this blog rss updates or register for mail updates!

    18 comments:

    Moish Ben Pashosh said...

    Thank you!
    Exactly what I needed!
    Mosish

    Anonymous said...

    Yaron,

    This is greatly appreciated. When using XSD I am still getting many errors - relating to gmd then gcd...

    PLease could you post the steps to create the final C# class? - or better still the class itself?

    Cheers

    Mike

    Yaron Naveh said...

    Mike

    If you extract the zip and in the vs command prompt go to "opengis_net_fixed\gml\3.2.1_Fixed"folder then run this:


    xsd.exe gml.xsd ..\..\xlink/1.0.0\xlinks.xsd ..\..\iso\19139\20070417\gmd\gmd.xsd ..\..\iso\19139\20070417\gco\gco.xsd ..\..\iso\19139\20070417\gss\gss.xsd ..\..\iso\19139\20070417\gts\gts.xsd ..\..\iso\19139\20070417\gsr\gsr.xsd /classes

    This should create the classes

    Yaron Naveh said...

    Maybe the formatting in the comments is not good - it is the same command as suggested here http://oegeo.wordpress.com/2008/04/10/importing-the-gml-321-namespace-into-net/

    Anonymous said...

    Yaron,

    The xsd.exe command you gave to build classes work only if you use GML 3.1.2. Can you please post the command for creating classes of GML 3.1.1. If you use the same command (even after fixing the resolution of directory), a lot of errors and warning come up.

    Cheers,
    Javed

    Anonymous said...

    Hi,

    Just an update. I have modified the command to the following:
    xsd.exe gml.xsd ..\smil\smil20.xsd ..\smil\smil20-language.xsd ..\..\..\xlink/1.0.0\xlinks.xsd ..\..\..\iso\19139\20060504\gmd\gmd.xsd ..\..\..\iso\19139\20060504\gco\gco.xsd ..\..\..\iso\19139\20060504\gss\gss.xsd ..\..\..\iso\19139\20060504\gts\gts.xsd ..\..\..\iso\19139\20060504\gsr\gsr.xsd /classes

    It causes less errors and warnings but still some errors left. Could you please have a look and see what else I can do.

    Cheers,
    Javed

    Yaron Naveh said...

    Anonymous

    Try this:

    xsd.exe gml.xsd ..\smil\smil20.xsd ..\smil\smil20-language.xsd ..\..\..\xli
    nk/1.0.0\xlinks.xsd ..\..\..\iso\19139\20060504\gmd\gmd.xsd ..\..\..\iso\19139\2
    0060504\gco\gco.xsd ..\..\..\iso\19139\20060504\gss\gss.xsd ..\..\..\iso\19139\2
    0060504\gts\gts.xsd ..\..\..\iso\19139\20060504\gsr\gsr.xsd ..\..\..\iso\19139\2
    0060504\gml\temporal.xsd ..\..\..\iso\19139\20060504\gml\basicTypes.xsd ..\..\..
    \iso\19139\20060504\gml\geometryBasic0d1d.xsd ..\..\..\iso\19139\20060504\gml\r
    eferenceSystems.xsd /classes

    Tom said...

    Hi Yaron,

    I have no experience whatsoever on GMX/XML with C#. I want to read Oracle spatial objects as GML 3.0. Can the classes you describe help me to create 3D geometry classes in C# from a GML 3.0 stream? And what would be the steps to do so?

    Cheers,

    Tom

    Yaron Naveh said...

    Hi Tom

    I do not have experience with the graphics itself so I cannot help. Generally the gml classes are just the model for the xml. Maybe there are other libraries that can actually create the graphic objects.

    Compukab said...

    Hi Yaron,

    I succesfully implemented the fixes working on a c# client in VS2008. I'm using the Java built service at http://www.dinoservices.nl/geo3dmodelwebservices-1/Geo3DModelService?wsdl. I've added it as a WebReference as suggested in one of your other posts.

    However, all the GML made available through this service seems to disappear in the proxy. Included is a response (to the listModels request) as seen by SoapUI:
    area xsi:type="ns2:PolygonType" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    ns2:exterior
    ns2:LinearRing srsName="urn:ogc:def:crs:EPSG::0"
    ns2:posList srsDimension="2"275550.0 531050.0 275550.0 514550.0 275550.0 498050.0 275550.0 481550.0 275550.0 465050.0 261050.0 465050.0 261050.0 448550.0 261050.0 432050.0 246550.0 432050.0 246550.0 415550.0 232050.0 415550.0 217550.0 415550.0 203050.0 415550.0 203050.0 399050.0 203050.0 382550.0 203050.0 366050.0 188550.0 366050.0 174050.0 366050.0 174050.0 349550.0 159550.0 349550.0 145050.0 349550.0 130550.0 349550.0 130550.0 366050.0 116050.0 366050.0 101550.0 366050.0 87050.0 366050.0 72550.0 366050.0 72550.0 349550.0 58050.0 349550.0 43550.0 349550.0 29050.0 349550.0 14550.0 349550.0 14550.0 366050.0 50.0 366050.0 50.0 382550.0 14550.0 382550.0 14550.0 399050.0 14550.0 415550.0 29050.0 415550.0 29050.0 432050.0 43550.0 432050.0 58050.0 432050.0 58050.0 448550.0 58050.0 465050.0 72550.0 465050.0 72550.0 481550.0 87050.0 481550.0 87050.0 498050.0 87050.0 514550.0 101550.0 514550.0 101550.0 531050.0 101550.0 547550.0 101550.0 564050.0 101550.0 580550.0 116050.0 580550.0 130550.0 580550.0 145050.0 580550.0 145050.0 597050.0 159550.0 597050.0 174050.0 597050.0 174050.0 613550.0 188550.0 613550.0 203050.0 613550.0 217550.0 613550.0 217550.0 597050.0 232050.0 597050.0 246550.0 597050.0 261050.0 597050.0 275550.0 597050.0 280050.0 597050.0 280050.0 580550.0 280050.0 564050.0 280050.0 547550.0 275550.0 547550.0 275550.0 531050.0/ns2:posList
    /ns2:LinearRing
    /ns2:exterior
    /area
    However, in the proxy class the model.area property contains an empty (null) exterior ring. Any ideas how and where this can happen?

    Marc

    Yaron Naveh (MVP) said...

    Compukab

    Try to create the model class from the proxy type and apply xml serialization on it. Then check how the serialized xml differes from the above (WRT the area element)

    Compukab said...

    Hi Yaron,

    Oops. This is way over my head for a first time Soap client developer. How do I create the model class from the proxy type and apply xml serialization on it?

    Marc

    Yaron Naveh (MVP) said...

    Marc

    Is there a wsdl to the web service? If so you should do "add web reference" from visual studio to create the client proxy.

    Compukab said...

    Hi Yaron,

    That's exactly what I did. I created the proxy from the wsdl (http://www.dinoservices.nl/geo3dmodelwebservices-1/Geo3DModelService?wsd) using add Web reference in VS. Then I applied the fixes (replacing double[] for string [] and replacing [][] with [] in the indicated places) you mentioned in reference.cs. Most of the proxy works OK, except for all the GML stuff. Any method that's supposed to return a geometry returns a Null. Using the SoapUI desktop client I noticed that the problem is not on the server side as SoapUI is able to retrieve the geometries. Any suggestions how to attack this problem?

    Marc

    Yaron Naveh (MVP) said...

    If you have a response which is relatively small please mail it to me, together with reference.cs

    Gerwin Postma said...

    @Marc,

    As i am developing for another part of the DinoService (uitwisselservice) and i'm encountering the same problem with .Net & GML, maybe we should contact ? Serialization from MultiSurfaceType does not play well as well as some other issues ..

    Mail me g.postma[at]nazcai.nl

    DragonMan said...

    This page saves me time and time again. Thanks!

    Philipp S. said...

    Hi,

    I use this command to build the c# classes. "xsd.exe gml.xsd ..\smil\smil20.xsd ..\smil\smil20-language.xsd ..\..\..\xli
    nk/1.0.0\xlinks.xsd ..\..\..\iso\19139\20060504\gmd\gmd.xsd ..\..\..\iso\19139\2
    0060504\gco\gco.xsd ..\..\..\iso\19139\20060504\gss\gss.xsd ..\..\..\iso\19139\2
    0060504\gts\gts.xsd ..\..\..\iso\19139\20060504\gsr\gsr.xsd ..\..\..\iso\19139\2
    0060504\gml\temporal.xsd ..\..\..\iso\19139\20060504\gml\basicTypes.xsd ..\..\..
    \iso\19139\20060504\gml\geometryBasic0d1d.xsd ..\..\..\iso\19139\20060504\gml\r
    eferenceSystems.xsd /classes "

    But i dont know which is the starting class to work with the XmlSerializer.

    So which type i have to use?
    XmlSerializer mySerializer = new XmlSerializer(typeof(???));