GIS and the Internet

							GIS and the Internet

 Web Mapping Services &
     Interoperability
Interoperability: the ability of two or more
systems or components to exchange information
and to use the information that has been
exchanged. - IEEE
        Standards-based GIS
• Until recently everyone is developing in
  their own little world (metadata => data => applications)
• From functionality to interoperability
• Internet is driving these changes: no net,
  then little reason to interoperate
• Being “open” is a strong selling point
           OpenGIS Consortium
    OGC is a collection of vendors, universities and government
    agencies interested bringing GIS to the mainstream through
    the development of open, interoperable systems.


•    No actual power, can only make recommendations
•    API specifications: GML, WMS, web context, WFS, WCS
•    Conformance testing and certification
•    University of Minnesota is a member
   Consider the Scenario...
• major hurricane bearing down on U.S. cost
• as GIS coordinator for a rural county you
  are required to put together a web site for
  citizens with things like NOAA GOES
  imagery, NWS NEXRAD mosaics and
  FEMA flood zones
• you don’t have those data, what do you do?
   …Consider the Scenario
• tell your boss, “Sorry, can’t do that”
• get on the phone/Internet and try to
  download the data
• make use of NWS/NOAA/FEMA services
  to integrate their data into your application
• enter the OGC Web Mapping Service
  specification
Traditional Architecture

 Resource 1    Application 1




 Resource 2    Application 2




 Resource 3    Application 3
Service-based Architecture

Resource 1               Application 1
             Service 1



Resource 2   Service 2   Application 2




Resource 3   Service 3   Application 3
        A Case for Services
•   abstraction of implementation
•   common access method (e.g. SOAP)
•   centralized security management
•   consistency of integration
    A quick word about XML
<contact>
• <name> based format
   text
    <first_name>Steve</first_name>
• “tags” are
Steve Lime used to markup unstructured
    <last_name>Lime</last_name>
   content
  </name>
Application Development Manager
  <title>Application Development Manager</title>
• <address>500 Lafayette “rules” are
   document structure
500 Lafayette Road Road</address> defined
   using schema or
  <city>St. Paul</city> document type definitions
St. Paul, MN 55155
  <state>MN</state>
   (DTDs)
651-259-5439, steve.lime@dnr.state.mn.us
  <zipcode>55155</zipcode>
  <phone_number>651-259-5439</phone_number>
  <email>steve.lime@dnr.state.mn.us</email>
</contact>
  Web Map Service (WMS)
• enables simple map creation and feature
  retrieval
• getCapabilties, getMap, getFeatureInfo
• cascading map servers
• equivalent to MapServer mode=map or
  mode=query
• current specification version is 1.3
        WMS - getCapabilties
• allows the server to advertise what it can do:
   –   available layers
   –   supported output projections
   –   supported output formats
   –   scale hints
   –   extent of data
• XML format (example)
                                 DNR Photo Server (getMap)



           WMS - getMap
• allows the retrieval of a map from a web
  server
• user supplies bounding box, image size,
  format, styling, error handling, etc…
• server responds with an “image”, typically
  a web-ready format like GIF, PNG or
  KML
     WMS – getFeatureInfo
• allows the retrieval of simple feature
  attributes
• user supplies an x,y coordinate pair and a
  layer of interest
• server responds with attribute information
  in HTML, GML or arbitrary ASCII format
             WMS Limitations
• all you get is a picture, not the data
• somewhat limited control over how the data is
  “styled” (see OGC SLD and Filter specs)
• particularly limiting with regards to labeling
• supports only a small (but ever increasing) portion
  of functionality typically supported by a vendor

that said…
 MapServer as WMS Server
• must compile software with Proj.4
• define METADATA block with the WEB
  object and any LAYERs
                    Map File Block
WEB
 …
 METADATA
  "wms_title" "MN DNR Orthorectified Fall CIR Photography"
  "wms_onlineresource" "http://maps.dnr.state.mn.us/cgi-bin/mapserv?map=DELI_WMS"
  "wms_srs" "EPSG:26915"
 END
END

LAYER
 NAME "cir“
 …
 METADATA
  "wms_title" "MN DNR Orthorectified Fall CIR Photography"
  "wms_srs" "EPSG:26915"
 END
END
 MapServer as WMS Client
• compile with PROJ.4, GDAL and libcurl
• define METADATA block within LAYER
• set LAYER CONNECTIONTYPE and
  CONNECTION properties
           Map File Block
LAYER
  NAME "prov_bound"
  TYPE RASTER
  STATUS ON
  CONNECTION "http://www2.dmsolutions.ca/cgi-bin/mswms_gmap?"
  CONNECTIONTYPE WMS
  METADATA
   "wms_srs" "EPSG:42304 EPSG:42101 EPSG:4269 EPSG:4326 EPSG:42304"
   "wms_name" "prov_bound"
   "wms_server_version" "1.1.0"
   "wms_format" "image/gif"
  END
END
Example WMS Browser
    Applications
 Web Feature Service (WFS)
• share vector data
• data returned as GML
• supports advanced query using OGC Filter
  specification
• enables transactional (insert, update, delete) access to
  data resources
• MapServer supports:
   – WFS server 1.0, GML2 & GML3
   – simple WFS client (via LAYERs)
   – read-only access (non-transactional WFS)
• Current specification version is 1.1
       WFS - getCapabilities
• allows the server to advertise what it can
  do:
  –   available layers or types
  –   supported output projections
  –   supported output formats
  –   extent of data
  –   supported query operators
• XML format (example)
WFS - describeFeatureType
• returns detailed information about a layer or
  group of layers
  – data elements
  – types and value domains
  – support for complex structures (e.g. address)
• format is an XML Schema (example)
           WFS - getFeature
• allows spatial queries, attribute queries or both
  against a layer
• response is typically a GML instance document
  that conforms to the describeFeatureType
  response of the server
• queries conform to the GML filter encoding
  standard
   – spatial, logical, and comparison operators
• equates logically to the various MapServer query
  modes
    WFS - Example Filters
<ogc:Filter>
    <ogc:PropertyIsGreaterThan>
       <ogc:PropertyName>AREA</ogc:PropertyName>
       <ogc:Literal>1000.00</ogc:Literal>
   </ogc:PropertyIsGreaterThan>
</ogc:Filter>

<ogc:Filter>
 <ogc:BBOX>
    <ogc:PropertyName>the_geom</ogc:PropertyName>
      <gml:Box
          srsName="http://www.opengis.net/gml/srs/epsg.xml#4326">
         <gml:coordinates>
             -90,40
             10.5,60
         </gml:coordinates>
      </gml:Box>
  </ogc:BBOX>
</ogc:Filter>
        Transactional WFS
• WFS-T, what WFS was really created for
• additional modes to lock features
  (getFeatureWithLock & lockFeature)
• supports INSERT, UPDATE and DELETE
  operations via transaction request
• relatively few commercial or open source
  solutions (MapServer is NOT one of them, see
  GeoServer instead)
Web Coverage Service (WCS)
• Share raster data
• Data returned using common formats such as
  GeoTIFF
• MapServer Supports:
   – WCS server 1.0
   – Ad-hoc access to tiled data by any attribute (e.g. cloud
     cover, date/time)
   – Raster re-projection and re-sampling
• Current specification version is 1.1
     Suggested Readings
• W3C - Intro to XML
• OGC Specification Documents:
  – Geographic Markup Language (GML)
  – Web Map Service (WMS)
  – Web Feature Service (WFS)
    • Styled Layer Descriptor (SLD)
    • Filters
  – Web Coverage Service (WCS)