Unclos Tutorial E. Baseline generation (Simplified)
The base line is needed in order to generate distance lines. The coast may also be used as a baseline (by changing the schema accordingly), but then the computing time may be very long.
If you do not have a base line for your area, you may generate a dummy to use as an approximation based on the coast line you imported in a previous exercise. If you already have imported an official base line you may skip this exercise.
Exercise: Generate dummy base lineUse the digitizer to snap values from the coastline, in order to make a "baseline". |
- Locate the coast line called GSHHS, which should have been imported in “1. Maritime Lines / Coast lines”
- Right click the data set and select “Make active”
- Open the Digitizer by selecting “Tools -> Quick digitizing” from the main menu.
- Check the option “Snap exclusively to active data points”. This will force the digitized points to stick to the points of the coast line
- Check the option “Save also in folder”, and click the Browse button
- The project view dialog will appear. Select the “Base lines” folder under “1. Maritime Lines”, and click ok
- Type in the name of your country and “dummy baseline” instead of “digitized_line” which will be the name of result line.
- Click “start digitizing”
- Digitize the points on the coast line, by clicking on the coast line with the left mouse button. The picks will automatically stick to the nearest point on the coast line data set. Digitize a rough version of the coast line by picking the outermost points on the coast line.
- When you are finished digitizing click the “stop digitizing” button. The digitized line should appear in the Base lines folder. If you are not happy with the digitized line and want to re-do the digitizing then you have to make the coast line active again before starting the digitizing.
- Locate the digitized base line in “1. Maritime lines / Base lines”
- Right click the dataset (not the folder), and select “set schema -> Base line”
Digitizing a baseline
An alternative is to use the command object "Red snapper" 
on the coast line and simply snap the outer points needed for a distance calculation.
Exercise: Use the "Red snapper"
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