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Exercise Title: Image Browsing/Harvesting in ncWMS Servers: GODIVA2
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Abstract: In this exercise you'll be introduced to ncWMS, the NetCDF "extension" to Web Mapping Services (WMS). Among other enhancements, ncWMS provides automatic color palette mapping to the grid value range, eliminating a tedious part of WMS development. The demonstration resources visited here only deliver images, which should be cured in subsequent versions.
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Preliminary Reading (in OceanTeacher, unless otherwise indicated):
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ncWMS Overview - OSGeo documentation
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ncWMS - "ncWMS is a Web Map Service for geospatial data that are stored in CF-compliant NetCDF files. The intention is to create a WMS that requires minimal configuration: the source data files should already contain most of the necessary metadata." From the University of Reading website, the center for ncWMS development. For example, the service maps stock color tables against the parameter value ranges, a feature not available in standard WMS.
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Required Software:
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Other Resources:
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GODIVA2 Demonstration Page - Main demo site, University of Reading
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SECOORA - Southeast Coastal Ocean Observing Regional Association. This regional-scale organization and system is one of the best global examples of cooperation and synthesis. The scope of products is startling, compared to the state of the art only 10 years ago.
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Author: Murray Brown
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Version: 10-26-13
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| 1. Although we will focus on the SECOORA clone, here is the main page for the GODIVA2 mother site. Note the typical menu of product groups on the left, and a map area with navigation. |
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| 2. Here's a closer look at the data menu, with one item opened to show typical parameters. Notice that the item AUTO-ZOOM ON SELECT is checked. |
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| 3. Here we've selected SEA WATER TEMPERATURE from the list above, and a map is drawn. The effect of the AUTO-ZOOM control is obvious, because GODIVA2 has zoomed into the actual data area, the Irish Sea. |
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| 4. This gives us a basic idea of how GODIVA2 works, so we'll move on to the SECOORA site, a regional organization of ocean observing systems in the southeastern USA. It includes the areas called the South Atlantic Bight and the eastern Gulf of Mexico (SABGOM). |
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5. Open the link to SECOORA and this is the data menu.
Items marked with (ERROR) have been polled by GODIVA2 and there is no response at this time, so you cannot obtain these data. We could look at the SABGOM products, but the global material is more interesting to us.
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6. Here we've opened the menu items for NOAA/NCEP GFS MODEL, just to see what's here.
This model was also used in MDL Exercise 9.13.
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| 7. Here we're looking at the SABGOM data products. This is a premier example of multi-agency cooperation, and state-of-the-art modeling. Please take the time to come back here and investigate these products. |
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8. Here we've opened the menu items for NOAA WAVE WATCH III, to see what's here. We're going to concentrate on this group for the rest of this exercise.
This model was also used in MDL Exercise 9.3.
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| 9. Here you should just click on SEA SURFACE WAVE SIGNIFICANT HEIGHT. After a short wait, a map similar to this should appear; try to find the exact same date. But make sure to find a date with at least one large dark area (meaning high waves). |
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10. Here's a closer look at the items above the map.
- HEIGHT - Elevation or depth of the visible data product; only zero for waves because they are at the sea surface
- FIRST FRAME/LAST FRAME - Dates and times to define an animation. If you begin to use these, then other items appear, related to the animation. You can try this, but be warned that it seems to be rather slow
- FIT LAYER - Same as AUTO-ZOOM
- MORE INFORMATION - Takes you to a complete THREDDS description page for the data; try this one to see what it includes. ncWMS is set up to run on THREDDS servers.
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| 11. Here's a look at the navigation controls above the map. You can't draw a zoom box with GODIVA2, so be ready to use just these controls. The globe icon returns you to global scale. The hand icon turns on the usual PAN function of your cursor. [The little 4-dot icon beside PAN is explained below.] |
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12. Here is the color scale. GODIVA2 has attempted to select the proper scale.
- You can manually insert values for the uppermost and lowermost value limits, or set them for, as an example, whole numbers
- LINEAR - Change between linear color scale and logarithmic scale. Log scale is better for mainly zero or near-zero values tapering off toward a small number of higher values, e.g. chlorophyll or sediment thickness.
- AUTO - Forces GODIVA2 to examine the data actually being viewed (possibly not the global values) and reset the minimum and maximum accordingly. Usually works, but you might have to adjust either of the limit values to eliminate any black areas (i.e. values outside the current range).
- LOCK - Locks or unlocks the color scale
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13. But where does the color scale come from? Click on the color scale you see in the previous panel, and these choices appear. The publisher has selected the basic palettes, but GODIVA2 matches them to the value ranges. This dynamic matching is not available in standard WMS.
NOTE: An apparent attempt to meld this capability into WMS is the publication of multiple different data products, each with its own static palette. You can see this in Panel 12 of MDL Exercise 8.9, which appears to be a selectable palette, but is actually a set of 10 different data products.
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14. And if you want to change the base map, click on the + to the left of the color table, and these possibilities appear.
- Try them with a given data layer to see what you like
- The POLAR items change the projection
- The OVERLAYS item turns off the data layer so you see only the map
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15. So move in on the largest storm feature on the map, indicated by the high waves. This will give you a chance to navigate without an actual zoom box.
When you have this map, you'll see perhaps that the highest values are not colored, but are black. This indicates they are just beyond the top value on the palette.
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| 16. You can manually increase the top value, a little at a time, as you see here. Not very much is needed. |
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| 17. Just keep checking the map to see what value just removes the black area. In this case the increase was only 0.14 m. This results in the wave height map. |
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| 18. A little tool we ignored above, but can look at now, is the icon with the four connected dots. This lets you select a pathway across the image where you can obtain wave values. |
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19. Click on the little icon to activate the function.
- Then click somewhere near a major data feature, such as the coast lf Greenland, northwest of the big wave area.
- Drag your cursor over the area of interest. You can make only one long track, or multiple "legs" with cursor clicks.
- When you come to the end you want, double-click to stop the function.
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20. This image of the wave height values encountered along the track appears. The image can be saved from this small window with a right-click; this image was saved in that way. This is a wonderfully fast way to get useful products directly from the data.
NOTE: The SECOORA folks are advised to change the graph line to bold black so it is more easily visible.
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21. What else can we do with the data map? Find these functions just below the map:
- TEST IMAGE - Full globe image without any labels or text
- GOOGLE EARTH - See next panel
- SCREENSHOT - Very clean map image with only necessary labels; best for publication
- OPACITY - 3 choices; useful if metocean features are over land
- PERMALINK - URL that opens this exact same map in any good browser
- EMAIL - Automatically creates an email that sends the PERMALINK to anyone
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22. Here, for example, is the PERMALINK. It is, in effect, the formula to make this map:
http://129.252.139.124/ncWMS/godiva2.html?menu=&layer=ww3_global/Thgt&elevation=0&time=2013-10-27T00:00:00.000Z&scale=0,14.95&bbox=-78.222656,16.347656,11.777344,86.660156
Click on it and see what happens.
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| 23. And here we've click on the Google Earth link to see how it looks. You can also save/send the KML link if you want, just like the PERMALINK above. |
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| 24. Finally, this author had believed that the ncWMS functionality would also include data saving capabilities, which would obviously be possible due to the use of THREDDS as the host server. This is not apparent here, yet, but it is hoped it will be included later. |
