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