RE: rotated grids / RE: redo striped.nc

• To: "Rob Cermak" <cermak@xxxxxxxxxxxx>, "Norman Barker" <nbarker@xxxxxxxxx>
• Subject: RE: rotated grids / RE: redo striped.nc
• From: "Woolf, A (Andrew)" <A.Woolf@xxxxxxxx>
• Date: Thu, 23 Jun 2005 20:40:32 +0100

FYI,
In our GML-based Climate Science Modelling Language (CSML), we extended
the gml:Grid type to deal with irregularly speaced (but rectangular)
grids by explicitly providing ordinate values of grid points, rather
than the 'offset' vectors appropriate for rectified grids. We also
included an efficiency mechanism for the case where grid axes are
aligned with coordinate system axes (i.e. non-rotated, but still
irregular).

The gory details (and they are) are in Sect 4.2.2 of the User's Manual
at http://ndg.nerc.ac.uk/csml/UsersManual.pdf, with an example below.

We think this model is a useful candidate for a future revision of GML.

<Grid srsName="urn:EPSG:geographicCRS:4326" srsDimension="2"
dimension="2">
 <gml:limits>
  <gml:GridEnvelope>
   <gml:low>-3 -2</gml:low>
   <gml:high>3 2</gml:high>
  </gml:GridEnvelope>
 </gml:limits>
 <gml:axisName>gridI</gml:axisName>
 <gml:axisName>gridJ</gml:axisName>
 <ordinate>
  <gridAxesSpanned>gridI gridJ</gridAxesSpanned>
  <sequenceRule order="+y+x">Linear</sequenceRule>
  <definesAxis xlink:href="#Lat"/>
  <axisValues>-3.54 -2.83 -2.12 -1.41 -0.70
-2.83 -2.12 -1.41 -0.707 0
-2.12 -1.41 -0.707 0 0.707
-1.41 -0.707 0 0.707 1.41
-0.707 0 0.707 1.41 2.12
0 0.707 1.41 2.12 2.83
0.707 1.41 2.12 2.83 3.54</axisValues>
 </ordinate>
 <ordinate>
  <gridAxesSpanned>gridI gridJ</gridAxesSpanned>
  <sequenceRule order="+y+x">Linear</sequenceRule>
  <definesAxis xlink:href="#Long"/>
  <axisValues>-0.707 -1.41 -2.12 -2.83 -3.54
0 -0.707 -1.41 -2.12 -2.83
0.707 0 -0.707 -1.41 -2.12
1.41 0.707 0 -0.707 -1.41
2.12 1.41 0.707 0 -0.707
2.83 2.12 1.41 0.707 0
3.54 2.83 2.12 1.41 0.707</axisValues>
 </ordinate>
</Grid>

> -----Original Message-----
> From: owner-galeon@xxxxxxxxxxxxxxxx 
> [mailto:owner-galeon@xxxxxxxxxxxxxxxx] On Behalf Of Rob Cermak
> Sent: 23 June 2005 18:11
> To: Norman Barker
> Cc: John Caron; galeon@xxxxxxxxxxxxxxxx
> Subject: rotated grids / RE: redo striped.nc
> 
> 
> > 
> > 
> > I am pleased that this has raised this question of Gaussian 
> grids!  We 
> > have rectified the
> > grid in X-Y for our datasets, but we have abused the 
> describeCoverage XML to explain the 
> > Z dimension as follows
> 
> And, not sure if this is the same issue, rotated grids?  
> Grids like #203  
> and also RUC2 grid #252.  No where near monotonic for lat and 
> lon and typically the only georeference information given is 
> a reference lat/lon 
> and reference lon as below:  
>   lat1: 16.281
>   lon1: 233.862
>   lov: 265.000
> 
> RUC2 #252:
> rec 1:0:date 2005062312 VGRD kpds5=34 kpds6=105 kpds7=10 
> levels=(0,10) 
> grid=252 10 m above gnd anl:
>   VGRD=v wind [m/s]
>   timerange 0 P1 0 P2 0 TimeU 1  nx 301 ny 225 GDS grid 3 
> num_in_ave 0 missing 0
>   center 7 subcenter 0 process 105 Table 2
>   Lambert Conf: Lat1 16.281000 Lon1 233.862000 Lov 265.000000
>       Latin1 25.000000 Latin2 25.000000 LatSP 0.000000 LonSP 0.000000
>       North Pole (301 x 225) Dx 20.318000 Dy 20.318000 scan 64 mode 8
>   min/max data -12.4 12.2  num bits 8  BDS_Ref -124  DecScale 
> 1 BinScale 0
> 
> Regridding is fine, but the preference is to maintain the 
> integrity of the 
> data in its original form.
> 
> > <RangeSet>
> >         <description>0.09999999403953552 0.19999998807907104 
> > 0.30000001192092896 0.5 0.699999988079071 1.0 2.0 3.0 5.0 7.0 10.0 
> > 20.0 30.0 50.0 70.0 100.0 150.0 200.0 250.0 300.0 400.0 500.0 600.0 
> > 700.0 850.0 975.0 1000.0 </description>
> > 
> >         <name>bands</name>
> >         <label>Pressure (hPa units) Levels</label>
> >         <axisDescription>
> >           <AxisDescription>
> >             <name>bands</name>
> >             <label>Bands/Channels/Samples</label>
> >             <values>
> > 
> >               <singleValue>1</singleValue>
> >               <singleValue>2</singleValue>
> >               <singleValue>3</singleValue>
> >               <singleValue>4</singleValue>
> >               <singleValue>5</singleValue>
> >               <singleValue>6</singleValue>
> > 
> > So that when you use the kvp BANDS then the client by indexing into 
> > the space-separated description list can calculate which physical 
> > level this corresponds to.
> > 
> > This is not an ideal solution, and I welcome comments on 
> how we can go 
> > about changing this.  Rectifying the grid to evenly spaced means a 
> > change to the original dataset (though it is necessary to make 
> > geotiff).
> > 
> > Hopefully this will be something that we can push into the GML in 
> > JPEG2000 coverage format.
> > 
> > Norman
> 
> -- 
> Rob Cermak : 907-474-7948 : FAX 907-474-7204 : PGP = 
> 0x75869A6E Alaska Ocean Observing System : Data Management 
> School of Fisheries and Ocean Sciences : University of Alaska 
> Fairbanks cermak@xxxxxxxxxxxx : fnjrc1@xxxxxxx 
> ED9U1M7P01@xxxxxxxxxx : cermak@xxxxxxxxxx
> 
>