Copyright © 2009, Open Geospatial Consortium, Inc. Web Services Report from the working group of 2nd Workshop on GIS/OGC Use in Meteorology Frédéric Guillaud, Marie-Françoise Voidrot OGC Met Ocean DWG, 71st OGC Technical Committee Mountain View, CA. USA December 9, 2009

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 2 WG - Services About 20 participants –ECMWF, met services, vendors, universities Two sessions of 1h30 Focus first on WMS and the time issue Aim: stick to existing standards whenever possible, and map met. vocabulary to existing dimension, to be compatible with other WMS client (e.g. validity time mapped to dimension) Note: –The “DIM_” prefix is only used in requests, not in GetCapabilities documents. The standard must make that clear and should not use “DIM_” when naming dimensions in the wiki or other documentation (see practice of other WG)

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 3 Time & Met data high rate refresh Consecutive calls to GetMap on the same layer may deliver different images: –When new observations are available (or corrected) –When a new model run is available Use of default (e.g. latest or “best”) –Most of the time latest = best –But will break caching –How often should a client call “GetCapabilities”? Could this information be provided as part of the GetCapabilities document itself? Or provide layer update frequency? (This may already be part of related metadata, e.g. associated WMO core record)

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 4 The time parallelogram (is not a rectangle…) Latest Same Same validity “Best” forecast Reference time Offset Future Past All possible valid dates only available in 5 runs out of 10

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 5 Time – Concepts & Vocabulary (forecasts) Run: –Base time, reference time, run (hour | time), run start time –Forecast reference time (CF) –We need a default (e.g. latest) for support for WMS clients Forecast time : –Valid time, validity time, verification time –(Just) Time (CF) –Proposal: GetCapabilities extents only contains the absolute date/time for the latest forecast Forecast period –Forecast offset, offset –Step : Step(n+1) = Offset(n+1) – Offset(n) Reuse GRIB2, BUFR or CF names when possible dimension is compulsory (in GetCapabilites)

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 6 Time – Vocabulary (forecasts ranges) Accumulation, Min/Max, averages,… –Practice: several… [Start offset, End offset] [Start, Start + range] [Middle – range/2, Middle + range/2] [End – range, End] –What is the validity time? Average: in the middle Accumulation: at the end Min, max? –Again, check what is done in CF, GRIB2, BUFR

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 7 Capabilities : Proposal 1 For a given, the dimension refers to the most recent T1,T2,T3 O1,O2,O3 R1,R2,R3 T1,T2,T3 which Ti= R3 +Oi All combinations of TIME/STEP/REF_TIME may not be valid Advantage: compatible with simple WMS clients

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 8 Proposal 1 (graphically …) Reference dates Valid dates ( ) Steps

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 9 Proposal 1.5 (best estimate time series) = ref. time followed by valid time Warning: Simple WMS clients will get different maps for the same when requested on different days. Reference dates Valid dates Steps

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 10 The time “parallelogram” revised … Intermediate runs with short forecast offset Last run still running … Step depends on the offset

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 11 Capabilities : Proposal 2 Use layer hierarchy, group all forecast of the same model for different runs Parent layers hold common attribute 1000/850/500 a0,a1, …,t1,t2,t3 t1,t2,t3 … t0,t1,t2 … … … Issue: difficult to manage (produce and use), generate large GetCapabilities. Compatible with existing WMS client Does not represent impossible combinations (unlike proposal 1) To be further explored…

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 12 Vertical coordinates (elevation) Several CRS : –“true” h (CRS:88) – often inappropriate, pressure, sigma, hybrid, flight level… –Native dimension “elevation” : e.g : 1000, 500, 200 Check for ISO compliance If not, Met Ocean needs to define missing vertical CRS (check with INSPIRE) How to mix levels types ? e.g : 1000hPa, 500hPa, 10m not standard? Any other ?

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 13 Other dimensions (1/2) When a layer needs to be parameterised, how to decided whether to use a new dimension, or make the parameter part of the layer name ? E.g : LAYER=ALADIN_ _36H_T_850 LAYER= ALADIN_T_850 DIM_RUN= T00:00:00Z DIM_FORECAST_OFFSET=36H LAYER=ALADIN DIM_RUN= T00:00:00Z DIM_FORECAST_OFFSET=36H DIM_LEVEL_TYPE=PRESSURE DIM_LEVEL_VALUE=850 DIM_PHENOMENON=T Caution : The granularity of the layers will impact : –The efficiency of catalogue searching –The size of GetCapabilities response and performances 6 offsets * 10 days * 20 levels * 20 phenomena = LAYERS !

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 14 Other dimensions (2/2) Should we agree on the names of all and the range of values of, or should WMS client be ready to support for any names –E.g. Should the name “forecast_probability_threshold” be agreed by the community –In short, should we give any semantic to dimension names, or are they just character strings WMS allow clients to ignore dimension Recommendation: MetOcean group to provide governance on dimension names (MetOcean checked if the dimension has already been proposed, process similar to CF convention)

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 15 General issues Layer names should not have any semantics –Semantics go in a dimension Tiles/Images should come back with associated metadata –Geo-location –Time –Other dimensions Notification –Availability of new model run

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 16 Other issues (not discussed) CRS –Vertical longitude of polar stereographic –Equirectangular BBOX spanning the anti-meridian Styles –SLD / SE (Symbology Encoding) sufficient for our community?

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 17 Other time topics out of the scope of the working group report (mentioned in the TWIKI and teleconferences) New issues raising out of the current works regarding climatology and observations

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 18 Time – Concepts & Vocabulary Climatology 3 variables (axis) can be introduced (according CF NetCDF conventions 1.4) : –“Cell Method” or “Statistical Process” : accumulations, averages, max/min, …) –“Climatological bounds” : statistics are computed over a time interval –Climatological statistics may also be derived from corresponding portions of a “range” of year (seasons), month, day, and therefore need a specific “climatological” axis e.g : –Average temperature for each climatological seasons over –Decadal max/min temperatures for January over –Hourly average temperatures are given for April –…

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 19 Proposals regarding the time issue for climatology The “statistical process” is not directly linked to the time issue, but can be handled with a specific dimension : CELL_METHOD Handle the climatological process period (or bounds) with the native TIME parameter (ISO8601 encoding) The rules for the “climatological axis” (dimension) are still to be discussed : –ISO19108 time ordinal reference system (TM_OrdinalEra within a TM_OrdinalRefecenceSystem) –Name of the dimension : CLIMATOLOGICAL_TIME ? –Grammar for values : Abbreviated or partial date time ( hyphen in place of omitted date elements), but not currently used : –E.g DIM_CLIMATOLOGICAL_TIME=-11- for November encoding YYYYMMDD Compliant ISO 8601:2000 but not ISO 8601:2004 ? (Provision removed)

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 20 Time – Concepts & Vocabulary Observations From OGC Observations & Measurements (07-022r1) –“Sampling Time” the time that the result applies to the feature-of-interest”. –“Result Time” “the time when the procedure associated with the observation act was applied” Other time properties –“Collection period” the time interval bounding all discrete observations within the collection –“ Process Period ” (part of the phenomenon definition ?) Time interval relative to validity time for accumulations, averages, max/min Similar to the climatological bounds E.g : rain accumulation over 3 hours –“Issue Time” Time at which the observation was published … allowing for amendments

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 21 Proposals regarding the time issue for observations Check consistency with Observations & Measurements model (OGC r1) Need to map time properties onto native WMS time parameter, dimensions or layer metadata Native time dimension would be used for SamplingTime or CollectionPeriod Possible dimension for “ProcessPeriod” Other time properties treat as metadata ?: –IssueTime, ResultTime,..

Helping the World to Communicate Geographically Copyright © 2009 Open Geospatial Consortium 22 Copyright © 2009, Open Geospatial Consortium, Inc. Thank you for your attention