D. Import Cultural and Bathymetric Data

Owned by Erlend Kvinnesland
Last updated: Sept 23, 2013
4 min read

Introduction

In this section we are going to import different cultural and bathymetric data in our area of interest. Geocap has two main import menus:

  • Generic - is used to import a number of different formats, such as images, grids, VTK etc. For a complete list of import formats look in the appendix: Generic Import Formats
  • ASCII (column) - can be used for many types text data files, e.g. whether the data columns have fixed or variable width, and also whether the coordinates are in X Y or Lat Lon. 

The import functionality in Geocap can be found on a folders right-click menu. Different import menues will be available based on the folders schema.

Exercises

 

 

A note on Coordinate Systems

When importing data into a project from different sources it is not uncommon that the data are in different datum and projections. The data sets that are to be loaded into this tutorial project are in UTM51S, some in UTM52S, and some in geodetic coordinates (latitude and longitude). A Geocap project has no restrictions on how the user chooses to store the data. Therefore, the data can be loaded and kept with their input geodetic settings. However in order to visualize and work efficiently with the data, it is necessary that the data is converted to the same datum and projection. This can be done using different conversion commands.

It is possible to view a datasets coordinate system by right-clicking it, selecting Properties and then the Geodetics tab. Sometimes this properties menu will be blank. It is then possible to set the coordinate system by clicking the Set geodetic meta data button. Note that this does not perform any conversion of the dataset.

In this tutorial project all the data shall be converted to UTM Zone 51S with the datum WGS84.

Bathymetry

The bathymetric grid we are importing in the next exercise is the global ETOPO1 which is publicly available from NGDC: http://www.ngdc.noaa.gov/mgg/global/global.html
For convenience we have already created a subset of the global grid, and downloaded it. We can import this grid using the Generic import.

 

Exercise

Import a bathymetric grid

  1. Locate the folder called Bathymetry in your Geocap project under 1. Cultural Data
  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 etopo1.asc in the \data\02etopo1 folder
  5. If Specify import area is checked, uncheck this option. This will import the entire grid.
  6. Click on the Reader Options tab and check the box next to Invert Z (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 Bathymetry folder.

The data is imported in Geodetic coordinate system, with latitudes and longitudes. Before we display this data we want to make sure it is in UTM zone 51S. 

Exercise

Convert the grid to UTM coordinate system

  1. Click the etopo1 dataset and go to the Shared commands section in the Toolbox.
  2. In the Operations folder double click the Convert to UTM... command
  3. Set the coordinate system to UTM zone 51 S
  4. Change the result combo box to Replace input.
  5. Click Execute.
  6. Agree to replace the existing dataset by clicking Yes.
  7. Geocap will report if the grid has been converted correctly, click OK and close the conversion dialog by clicking Cancel.
  8. 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

Coastline

The coastline we are importing in the next exercise is the global GSHHG coastline which is also publicly available from NGDC: http://www.ngdc.noaa.gov/mgg/shorelines/gshhs.html
The dataset we are importing contains the whole world, so you will have to import specify the area of interest when importing this.

Exercise

Import and display coast line

  1. Right click the Coastline folder and select Import > Generic….
  2. The format should be set to Automatic.
  3. Click the browse button and locate the folder \data\01coastline
  4. Select the file called gshhs_f.b and click Open.
  5. Click the Area of Interest tab.
  6. Check the Import Area check box.
  7. Type in the minimum and maximum latitude and longitude in decimal degrees.
    1. Min Y: -23, Max Y: -13, 
    2. Min X: 113, Max X:123
  8. Click Execute.
  9. Geocap will recognize the datum and coordinate system of the file. If it doesn't, it will ask you to specify this. In that case select datum: World Geodetic System 1984 and coordinate system: Geodetic.
  10. Geocap will confirm that the file has been read. Click OK.
  11. After the file has been read, click the Cancel button in the Generic reader dialog.
  12. Observe that the imported dataset is stored in the Coastline folder.
  13. Right click the dataset and select Zoom to Data
  14. Right click the dataset and select Display

Notice that the coastline is not displayed together with the grid. This is because your coast line is still in Geodetic coordinates.

Exercise

Convert coastline to the right projection

  1. Click the coast line dataset and go to the Shared commands section in the Toolbox.
  2. In the Operations folder double click the Convert to UTM... command
  3. Set the coordinate system to UTM zone 51 S
  4. Change the result combo box to Replace input.
  5. Click Execute.
  6. Agree to replace the existing dataset by clicking Yes.

The data is now converted and re-displayed in new the coordinate system.