Data Overlays

CDAT shows graphics in the data view using overlays, which are layered on top of the data image.  To show a latitude/longitude grid, coastlines, and to mask low quality SST data, click the  Overlay Layers control tab, then:

1. Click the  Coast button to add a coastline.
2. Click the  Grid button, and then Lat/Lon for a latitude/longitude grid.
3. Click the  Mask button, and then  Expression mask.  An overlay properties window will appear — type quality_level < 5 in the mask expression text field, then click OK.

Your CDAT window will look similar to the following:

The data view is more useful now but doesn't look correct.  The mask data is rendering on top of the coast and grid lines. The Overlay list shows the overlay layers as if they're a stack, rendered from bottom to top.  Try rearranging the overlays by selecting an overlay (click on its right side) and use the  Move Up and  Move Down buttons to rearrange the overlays until the CDAT window looks as follows:

Bonus exercises:

• Try changing the overlays' drawing color, line style, or fill color.  You can also change the name to help remember the overlay contents, ie: Quality mask instead of Expression mask 1.
• Double-click on the right of the overlay in the list to reveal a properties window with other properties to change.  You can also select an overlay and click the  Edit Properties button.
• Try deleting all the overlays in the list using the  Delete button.  Now, open the Oceanographic overlay group in the bottom panel.  The list now contains some useful overlays (but not a quality mask, though you could add one in the same way as Step 3 above).
• Watch a YouTube video Links to an external site. on data overlays.