You can add topographic and bathymetric contour lines to the data view using a topography overlay. Contours are computed on-the-fly from a built-in data file containing ETOPO 5-minute resolution elevation data. In this exercise we'll use the ocean currents data file example_altim_surface_curr_feb_2023.nc and render sea level anomaly with bathymetric contours.

Start by opening the data file and loading the sla variable. Change the palette to Ocean-balance and the range from -1.0 to 1.0. Then add coastlines, lat/lon lines, and zoom in to northeastern Australia. The data view should look similar to the following:

CDAT window showing sea level anomaly data off the coast of northeast Australia

To add and edit a topography overlay, do the following:

Click the Overlay button in the toolbar, then Topographic and bathymetric contours. By default a topography overlay with 200 m and 2000 m depth contours is created.
Select the new Topography 1 overlay in the Overlay List and click the Edit button — an overlay properties window will appear.
Turn on the Draw line drop shadow check box.
Remove the -200 and -2000 entries in the list by selecting them and using the Remove button.
Add contours for -500, -200, -100, 100, 200, and 500 using the text field under the Levels list. You can type each one and hit the Enter key or click the Add button.
Click OK to accept all the changes.
Move the new topography overlay to the middle of the list between the coast and lat/lon overlay using the Move Down button. That way the topography lines render on top of the land polygons.

You should now see a data view similar to the following:

CDAT windows showing northeast Australia sea level anomaly data with bathymetric and topographic contours

NOTE: Use caution with rendering topography overlays in a large area such as a global data view. It's best to avoid this because it can take a significant time for CDAT to create and render many contours over such a large area, and can also fail to render properly.

Bonus exercises:

Try opening another data file and adding a topography overlay for your own area of interest.
View topographic elevation data directly by opening the ETOPO data file in your CoastWatch Utilities installation directory <INSTALLDIR>/data/noaa/coastwatch/render/etopo5.hdf.
As of version 4.0.0 of the CoastWatch Utilities, a 1 km ETOPO data file is also availalble from the CoastWatch Utilities distribution page under the Data Tools section of the CoastWatch central operations website.
Search online for other sources of topographic contour data that you can use in the next exercise on shape overlays.