.. index:: pair: WMS Server; Time requests .. _wms_time: ***************************************************************************** WMS Time ***************************************************************************** :Author: Jeff McKenna :Contact: jmckenna at gatewaygeomatics.com :Revision: $Revision$ :Date: $Date$ :Last Updated: 2006/06/26 .. contents:: Table of Contents :depth: 2 :backlinks: top Introduction ============ A WMS server can provide support to temporal requests. This is done by providing a TIME parameter with a time value in the request. MapServer 4.4 and above provides support to interpret the TIME parameter and transform the resulting values into appropriate requests. Links to WMS-Related Information -------------------------------- - :ref:`MapServer WMS Server HowTo ` - :ref:`MapServer WMS Client HowTo ` - `WMS 1.1.1 specification`_ - `MapServer OGC Web Services Workshop`_ Enabling Time Support in MapServer ================================== Time Patterns ------------- WMS specifies that the basic format used for TIME requests is based on the ISO 8601:1988(E) "extended" format. MapServer supports a limited set of patterns that are defined in the ISO 8601 specifications, as well as few other patterns that are useful but not compliant to ISO 8601. Here is a list of patterns currently supported: **Table 1. Supported Time Patterns** ==================== ==================== Time Patterns Examples ==================== ==================== YYYYMMDD 20041012 YYYY-MM-DDTHH:MM:SSZ 2004-10-12T13:55:20Z YYYY-MM-DDTHH:MM:SS 2004-10-12T13:55:20 YYYY-MM-DD HH:MM:SS 2004-10-12 13:55:20 YYYY-MM-DDTHH:MM 2004-10-12T13:55 YYYY-MM-DD HH:MM 2004-10-12 13:55 YYYY-MM-DDTHH 2004-10-12T13 YYYY-MM-DD HH 2004-10-12 13 YYYY-MM-DD 2004-10-12 YYYY-MM 2004-10 YYYY 2004 THH:MM:SSZ T13:55:20Z THH:MM:SS T13:55:20 ==================== ==================== Setting Up a WMS Layer with Time Support ---------------------------------------- To have a valid WMS layer with time support, the user has to define the following metadata at the layer level: - *wms_timeextent*: (*Mandatory*) this is used in the capabilities document to return the valid time values for the layer. The value defined here should be a valid time range. (more on this in 'Specifying Time Extents' below) - *wms_timeitem*: (*Mandatory*) this is the name of the field in the DB that contains the time values. - *wms_timedefault*: (*Optional*) this value is used if it is defined and the TIME value is missing in the request. It is also recommended to set a :ref:`LAYER` `FILTER` for the time layer to provide a default time also for non-WMS requests. If the time item is `mytime`, and the time format is "YYYYMMDD" the following layer filter could be used: .. code-block:: mapfile FILTER ([mytime] = '2004-01-01 14:10:00') Specifying Time Extents *********************** Time Extents can be declared with the following syntax for the *wms_timeextent* metadata (see Annex C.3 in the `WMS 1.1.1 specification`_ document for a full description): 1. *value* - a single value. This is not directly supported in MapServer but there is an easy workwound by specifying the same value as min and max. 2. *value1,value2,value3,...* - a list of multiple values. 3. *min/max/resolution* - an interval defined by its lower and upper bounds and its resolution. This is supported in MapServer (note that the resolution is not supported however). 4. *min1/max1/res1,min2/max2/res2,...* - a list of multiple intervals. Example WMS-Server Layer ************************ .. code-block:: mapfile LAYER NAME "earthquakes" METADATA "wms_title" "Earthquakes" "wms_timeextent" "2004-01-01/2004-02-01" "wms_timeitem" "TIME" "wms_timedefault" "2004-01-01 14:10:00" "wms_enable_request" "*" END TYPE POINT STATUS ON DATA "quakes" FILTER ([TIME]='2004-01-01 14:10:00') CLASS .. END END GetCapabilities Output ---------------------- If your layer is set up properly, requesting the capabilities on the server outputs a Dimension element. Here is an example of a GetCapabilities result for a layer configured for time support: .. code-block:: guess earthquakes Earthquakes EPSG:4326 2004-01-01/2004-02-01 Supported Time Requests ----------------------- When sending a request with the TIME parameter, different types of time values can be specified. The following are supported by MapServer: - *single value*: for example: ...&TIME=2004-10-12&... - *multiple values*: for example: ...&TIME=2004-10-12, 2004-10-13, 2004-10-14&... - *single range value*: for example: ...&TIME=2004-10-12/2004-10-13&... - *multiple range values*: for example: ...&TIME=2004-10-12/2004-10-13, 2004-10-15/2004-10-16&... Interpreting Time Values ------------------------ When MapServer receives a request with a TIME parameter, it transforms the time requests into valid expressions that are assigned to the filter parameter on layers that are time-aware. Here are some examples of how different types of requests are treated (wms_timeitem is defined here as being "time_field"): - single value (2004-10-12) *transforms to* (\`[time_field]\` eq \`2004-10-12\`) - multiple values (2004-10-12, 2004-10-13) *transform to* (\`[time_field]\` eq \`2004-10-12\` OR \`[time_field]\` eq \`2004-10-13\`) - single range : 2004-10-12/2004-10-13 *transforms to* ((\`[time_field]\` ge \`2004-10-12\`) AND (\`[time_field]\` le \`2004-10-13\`)) - multiple ranges (2004-10-12/2004-10-13, 2004-10-15/2004-10-16) *transform to* ((\`[time_field]\` ge \`2004-10-12\` AND \`[time_field]\` le \`2004-10-13\`) OR (\`[time_field]\` ge \`2004-10-15\` AND \`[time_field]\` le \`2004-10-16\`)) As shown in the above examples, all fields and values are written inside back tics (`) - this is the general way of specifying time expressions inside MapServer. **Exceptions to this rule:** 1. When dealing with layers that are not Shapefiles nor through OGR, the expression built has slightly different syntax. For example, the expression set in the filter for the first example above would be ([time_field] = '2004-10-12'). 2. For :ref:`input_postgis` layers, the time expression built uses the *date_trunc* function available in PostgreSQL. For example, if the user passes a time value of '2004-10-12', the expression set in the filter is date_trunc('day', time_field) = '2004-10-12'. The use of the date_trunc function allows requests to use the concept of time resolution. In the example above, for a request of '2004-10-12', MapServer determines that the resolution is "day" by parsing the time string and the result gives all records matching the date 2004-10-12 regardless of the values set for Hours/Minutes/Seconds in the database. For more information on the date_trunc function, please refer to the `PostgreSQL documentation`_. Limiting the Time Formats to Use -------------------------------- The user has the ability to define the time format(s) to be used when a request is sent, in metadata at the WEB level. For example, the user can define the following two formats: .. code-block:: mapfile "wms_timeformat" "YYYY-MM-DDTHH, YYYY-MM-DDTHH:MM" Another example is for a WMS layer that is based on time data that contains precise time values taken every minute (e.g., 2004-10-12T13:55, 2004-10-12T13:56, 2004-10-12 T13:57, ...). Normally, a valid request on such a layer would require the time value to be as complete as the data underneath. By defining a set of patterns to use, MapServer introduces the notion of resolution to be used when doing a query. Using the example above, a request TIME= 2004-10-12T13:55 would be valid and a request TIME= 2004-10-12T13 would also be valid and would return all elements taken for that hour. Note that this functionality is only available on layers based on Shapefiles and OGR. Example of WMS-T with PostGIS Tile Index for Raster Imagery ----------------------------------------------------------- This example currently requires latest 4.9 CVS build! Here is an example mapfile snippet for a raster WMS-T instance using a PostGIS tileindex. This example shows US Nexrad Base Reflectivity running at Iowa State U at http://mesonet.agron.iastate.edu/cgi-bin/wms/nexrad/n0r-t.cgi?SERVICE=WMS&request=GetCapabilities .. code-block:: mapfile :linenos: # Tile Index LAYER STATUS ON NAME "time_idx" TYPE POLYGON DATA "the_geom from nexrad_n0r_tindex" METADATA "wms_title" "TIME INDEX" "wms_srs" "EPSG:4326" "wms_extent" "-126 24 -66 50" "wms_timeextent" "2003-08-01/2006-12-31/PT5M" "wms_timeitem" "datetime" #column in postgis table of type timestamp "wms_timedefault" "2006-06-23T03:10:00Z" "wms_enable_request" "*" END CONNECTION "dbname=postgis host=10.10.10.20" CONNECTIONTYPE postgis END # raster layer LAYER NAME "nexrad-n0r-wmst" TYPE RASTER STATUS ON DEBUG ON PROJECTION "init=epsg:4326" END METADATA "wms_title" "NEXRAD BASE REF WMS-T" "wms_srs" "EPSG:4326" "wms_extent" "-126 24 -66 50" "wms_timeextent" "2003-08-01/2006-12-31/PT5M" "wms_timeitem" "datetime" #datetime is a column in postgis table of type timestamp "wms_timedefault" "2006-06-23T03:10:00Z" "wms_enable_request" "*" END OFFSITE 0 0 0 TILEITEM "filepath" #filepath is a column in postgis table with varchar of the filepath to each image TILEINDEX "time_idx" FILTER ([datetime] = "2006-06-23T03:10:00Z") END You can find more information on Time and tileindexes in the :ref:`WCS documentation `. Future Additions ================ - Support for a special time value: "current". Limitations and Known Bugs ========================== - Pattern "YYYYMMDD" does not work on Windows. (`Bug#970`_) .. #### rST Link Section #### .. _`WMS 1.1.1 specification`: http://www.opengeospatial.org/docs/01-068r2.pdf .. _`MapServer OGC Web Services Workshop`: http://ms-ogc-workshop.maptools.org/ .. _`PostgreSQL documentation`: http://www.postgresql.org/docs/8.1/static/functions-datetime.html .. _`Bug#970`: http://trac.osgeo.org/mapserver/ticket/970