Page Comparison

Download the ETOPO1 grid from the Internet

1. Open a web browser, and go to the following address: http://www.ngdc.noaa.gov/mgg/global/global.html
2. Click the link: Extract Custom Grids - in the left column on the page, below the globe. A new web page with a interactive map should appear.
3. Zoom into the area where you want to extract the grid.
4. Click the icon with and i in the upper left corner of the map window.
5. Drag a rectangle over the area where you want to extract the grid. You should see a red rectangle on the map.
6. Keep Layer as ETOPO1 (ice)
7. Select Output Format XYZ
8. Click "click here to download"

Import the grid into a folder in your project

1. Locate the folder called Grids in your Geocap project under 2. Seabed
2. Right click the folder and select Import > Generic…
3. The format should be set to Automatic.
4. Click the browse button and locate the file you downloaded in the previous exercise.
5. If Specify import area is checked, uncheck this option. This will import the entire grid.
6. Click on the Reader Options tab and under polydata and check the box next to Invert (The Grid we will import has negative values for sea depths, and positive values for heights above sea level.  Usually bathymetry data has positive values for depths.  We therefore have to multiply the depth and height values by -1 with this option to "flip" the data).
7. Click Execute.
8. You will now be prompted with a question of the coordinate system and datum. Select: World Geodetic system 1984, Geodetic and click OK.
9. Geocap will report if the grid has been imported correctly; click OK and close the import dialog by clicking Cancel.
10. Observe that the new data set has appeared in the Grids folder.

Convert the grid to Mercator coordinate system

The data is imported in Geodetic, with latitudes as Y coordinates and longitudes as X coordinates.  In order to view the grid with the data we have already imported and converted to a Mercator coordinate system, we need to convert this grid to match the same coordinate system as the other data in the project (Mercator).

1. Click the dataset and go to the Shared commands section in the Toolbox.
2. Double click the Convert to Mercator... command in the Operations folder. (or another relevant datum / coordinate system)
3. Change the result combo box to Replace input.
4. Click Execute.
5. Agree to replace the existing dataset by clicking Yes.
6. Geocap will report if the grid has been converted correctly, click OK and close the conversion dialog by clicking Cancel.
7. Check that the schema of the dataset is seabed surface.  If not then right click the dataset, choose Set Schema and choose seabed surface.

The data is now converted and ready to be displayed:

1. Right click the dataset and select Zoom to Data
2. Right click the dataset and select Map Sea
3. Right click the dataset and select Map Land

Crop out smaller grids from your Seabed surface

• Use the command Crop to chop out 2-4 smaller grids from your main seabed surface.

Use keyboard shortcut z in 2d mode to set a window frame

Display a detailed contour pattern on the seabed surface

Use the command General Display to display contours. Try to display line contours at depths relevant to base of slope and see if you can observe the area of the deep ocean floor and areas of base of slope from the contour pattern.

Explore the different display options of this command, and observe that this command is different from most other commands. Observe that this command can produce several actors (visualizations).

Generate a Bathymetric Profile from a grid

1. Locate the dataset you imported in the previous exercise, which should be located in 2. Seabed / Grids.  The data set should have the schema Seabed Surface.  If it does not have this schema, right click it and select Set Schema > Seabed Surface.
2. Display the seabed by right clicking it and selecting Map Sea.
3. Right click the dataset and select the command Display contours...
4. A menu will appear. We will just use the default settings.  Click Execute, and Cancel.
5. Right click the dataset and select the command Generate Bathymetric Profile.  A menu will appear.
6. Click the Start button, then digitize the first point of the profile by clicking with the left mouse button where you want the profile to start on the seafloor in the display window.
7. Digitize the last point of the bathymetric profile by clicking with the left mouse button where you want the profile to stop on the seafloor.
8. After you have digitized both the start and stop point, you will be prompted with a dialog asking you to provide a name for the profile.  Keep the default name and click OK.
9. Geocap will notify you where the resulting Bathymetric profile has been stored in the project.  Click OK.
10. Locate the new profile in 2. Seabed / Bathymetric Profiles; this is the default position of bathymetric profiles.  In order to structure our project we want to move the profile into a sub folder and rename the profile.
11. Right click the folder 2. Seabed / Bathymetric Profiles and select New > Folder.
12. Change the folder name to Etopo1 and click OK.
13. Right click the profile and select Cut.
14. Right click the new folder and select Paste.  The profile is now moved into the new folder.
15. Right click the data set and select Rename.  Give the profile a suitable name, for example the name of the area you are working in.