Marine Data Literacy

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Home > 9. Operational/Synoptic > 9.11 Panoply/Google

9.11 Converting Grids and Motion Vectors to Google Earth Format, Using Panoply

IMPORTANT NEW INFORMATION:  Recently the Saga GIS software has been shown to deal quite adequately with most NetCDF (NC) data grids (and possibly also GRIB files).  This should be viewed as a useful addition to the rapid, direct NC analysis and display capabilities of Panoply (see below).  If you are also interested in this route for your data, then please check Viewing and Managing Well-Formed NetCDF Grids in Saga.
1.  Download the above 2 KML files to the folder PRODUCTS > SAGA > VECTORS.  Download the NetCDF data files to DATA > OCEAN.
2.  Unzip the 2 gz files, in place, to reveal their NetCDF contents
3.  Run Panoply, and open the file Notice that all the data objects within the NC file are listed.  But Panoply can only visualize objects that have the annotation [lon][lat] in their TYPE column.  In this case only one object complies, and that is the sea surface height, or H.
4.  Select the sea surface height (H) and click on CREATE PLOT to see this graphic in a new window, entitled H.
5.  Click near the bottom of the graphic to reveal a set of 5 control tabs that allow you to modify the graphic.
5.  Select the MAP tab, and make these choices to make the graticule invisible.
4.  Select the SCALE tab to make these choices to make the H data invisible.
5.  Now you have a nice, generic white globe, with vaguely correct continental boundaries.  Notice that the arctic is shown as solid land, major lakes and inland seas are not shown (including the mediterranean!).  But this will serve our purposes right now.

On your own time, you can search for a better global figure, if necessary for your own projects.

6.  Select FILE > EXPORT KMZ and navigate to the folder PRODUCTS > PANOPLY to save the graphic with the name globe_white_low_res_countries.kmz
7.  In Windows Explorer, find the new KMZ file and double-click on it to open it in Google Earth.
8.  Select FILE > OPEN to add the world borders KML version, from above.
9.  Also add the global 10-degree graticule.
10.  If you want to change the color of the graticule, then you have to it carefully.  First, open the graticule folder in the list of temporary places.  You'll find inside a single vector object named GRATICULE.

Right-click on this object, and select PROPERTIES.

NOTE:  We aren't sure, due to the skimpy documentation, but apparently when you're editing PROPERTIES it is best to do it at the data object level and not at the folder level.

11.  This edit window opens.  Click on STYLE, COLOR.
12.  This window states that the GRATICULE object has sub-objects (i.e. the individual lines), so you must decide if they will also be edited here.

Click SHARE STYLE to confirm that changes here will also apply to sub-objects.

13.  We are not sure that it is required, but we recommend that you change the OPACITY of the object to 50% here.

Then click on the white box beside COLOR.

14.  In this color-selection page, click on BLACK and then select OK.
15.  The graticule lines are now black.
16.  Select FILE > SAVE IMAGE AS and then save this basic globe with the name globe_countries_graticule_basic.kmz
17.  Return to the SCALE tab at the bottom of the page, and change the COLOR TABLE to the PANOPLY GCT palette.
18.  Now you should see approximately the same global figure as before.
19.  Click near the bottom of the graphic to activate the tabs menu, then select the MAP tab.
20.  Within the "projections" is actually the function that allows you to subset the data.
21.  And here's how you select the region:
  • For CENTER ON LON, enter the longitude exactly midway in your area of interest; use the -180 to + 180 convention
  • For CENTER ON LAT, enter the latitude exactly midway in your area of interest; use the -90 to +90 convention
  • For WIDTH use the exact longitudinal width of your area of interest
  • For HEIGHT use the exact latitudinal height of your area of interest
  • Don't click FIX PROPORTIONS, or Panoply might make automatic changes in your values

You might have to repeat one of these settings to get Panoly to complete the calculations and actually display the desired area.

22.  And here is the sea surface height, H, for Liberia.
23.  Select FILE > EXPORT KMZ and then save this image with the name Grid_0001 in nrt_global_merged_madt_h_2011052_aviso.kmz
24.  In Google Earth, use FILE > OPEN to show the new KMZ image in place.

Unfortunately the Liberia area isn't very dynamic, in terms of H, but you can see the obvious utility of this method for other areas.

25.  In addition to the display of a single grid, as seen above, Panoply can work with 2 grids simultaneously.  This is particularly important to us, because one of the 2-grid functions is the display of motion vectors from U and V component grids.  We'll learn how to do this in the next few panels.
26.  You can close the NetCDF H grid, and open the NetCDF UV grid.

Select and double-click on the U component grid to open it.

27.  Here is the U grid.  You can see the typical strong east-west bands near the equator.
28.  Now on the SOURCES page, select the V grid.
29.  Right-click on the CREATE PLOT icon, and select COMBINE IN XXXX function (referring to the previously loaded U portion of the grid).
30.  Here you can see that the title below the graphic refers to both the U and V grids, indicating successful loading of both grids.
31.  Click near the bottom of the graphic to open the settings tabs, and select ARRAY(S).  Then open the menu of PLOT MAPS to select VECTOR MAGNITUDE.
32.  The vector arrows immediately appear, but typically they are too small or too large.
33.  Open the CONTOURS & VECTORS tab and adjust the SCALE LENGTH.  Smaller values make larger arrows; larger values make smaller arrows.
34.  Here is the result from setting the SCALE LENGTH to 25.  You might have to fiddle with another setting to get this change to become visible.
35.  Now, just as you did in Panel 21 above, display only the Liberia area of interest.

Notice that the arrows are much close together, indicating that automatic thinning of the arrows was in effect in Panel 34 above.

36.  Now, remove the color palette, as you did in Panel 4 above.
37.  Select FILE > EXPORT KMZ and navigate to PRODUCTS > PANOPLY to save the vectors as Grid_000_in_nrt_global_merged_madt_uv_201105_aviso.kmz
38.  In Google Earth, use FILE > OPEN to visualize this new KMZ file.  It is an image, so you cannot see the scalar H grid below it.
39.  To "see through" the vectors image, right-click on the vectors object and select PROPERTIES.  Then set the TRANSPARENCY to about 50%, as you see here.
40.  Although this is not an ideal solution, as the use of a real vector file for the arrows would provided, it is acceptable.
41.  So the above display options are available and useful for NetCDF grids.  GRID files could also be displayed, using exactly the same methods.



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