The goals of this session is to show how to draw lines and symbols making use of the rich pen attributes and fill options.
Our final figure with an assemble of line styles
How to create it? Open a terminal and the VisualStudio editor. In the editor type
#!/usr/bin/env bash
# Examples of lines with different pen settings
gmt begin lines png
# Create a file with the line start and end points
echo 0 0 > t.dat
echo 10 1 >> t.dat
# Plot a continuous red line with thickness of 1 point (1 point = 1/72 inch)
gmt plot t.dat -R-1/11/-1/11 -JX14 -Baf -BWSen -W1,red
gmt end show
Run the script and will see this boring figure
Now add instructions to plot another line
echo 0 1 > t.dat
echo 10 2 >> t.dat
gmt plot t.dat -W3,green
Note that we generate the line again to not everlap the first one
The script that plots all lines (some are less boring, we hope) is lines.sh.
At the end we will generate this figure
In your text editor create a script with
#!/usr/bin/env bash
# Examples of symbols with different filling and outline pens
gmt begin symbols png
echo 0 0 | gmt plot -R-1/6/-1/6 -JX15/15 -BWSen+t"Symbols & pens" -Ba2g1 -Ggreen -Sc0.75c
echo 1 0 | gmt plot -Ggreen -W1,black -Sc0.75c
echo 2 0 | gmt plot -Ggreen -W1,0/130/0 -Sc0.75c
echo 3 0 | gmt plot -Ggreen -W1,black,dashed -Sc0.75c
echo 4 0 | gmt plot -Ggreen -W1,black,-. -Sc0.75c
echo 5 0 | gmt plot -G- -W1,0/130/0 -Sc0.75c
gmt end show
This plots circles with the same size (0.75 cm diameter) and different colors and outline pens
adding these more plots other symbols (star, diamond, square, etc...)
echo 0 1 | gmt plot -Gred -W1,black -Sa0.75c
echo 1 1 | gmt plot -Gred -W1,black,dashed -Sc0.75c
echo 2 1 | gmt plot -Gred -Sd0.75c
echo 3 1 | gmt plot -Gred -W0.5,black -Sh0.75c
echo 4 1 | gmt plot -W2,red -S+0.75c
echo 5 1 | gmt plot -Gred -Ss0.75c
but when things start to be more interesting is when we make use of GMT's own custom symbols.
There is a default set of custom symbols
that comes with GMT and several more contributed by users (wales and dolphins,
geological)
and you can even build your own symbols using the symbols macro language
Add this and we get another row, this time with the custom symbols
echo 0 3 | gmt plot -Gbrown -W1 -Skflash/1.5c
echo 1 3 | gmt plot -Gblue -W1 -Skhurricane/1.5c
echo 2 3 | gmt plot -Ggray -W1 -Skpacman/1.5c
echo 3 3 | gmt plot -Gbrown -W1 -Skstar3/1.5c
echo 4 3 | gmt plot -Gyellow -W1 -Sksun/1.5c
echo 5 3 | gmt plot -Gred -W1 -Skvolcano/1.5c
For even more elaborated symbols we can use EPS (encapsulated Postscript) files directly.
These two are stored in the GMT server and will be download directly by GMT (the leading @ is
the responsible for that automatic download).
echo 1 5 | gmt plot -Sk@gallo/3.5c
echo 4 5 | gmt plot -Sk@sardinha/6c
The full script that plots all symbols displayed at the begining of this topic can be found here symbols.sh.
To exemplify how to paint polygons we will extract the outline of Italia and use it in our example. In the editor create a script called italia_I.sh with
#!/usr/bin/env bash
# Extract the ouline of mainland Italia and use it as example for filling polygons
# The more cryptic command to extract the polygon is due to the fact that for demonstration
# sake we only want the main country polygon (i.e., drop all islands and islets)
gmt pscoast -EIT -M | gmt convert -C+l3000 -bof > italia.bin
gmt begin italia_I png
gmt plot italia.bin -bi2f -R6/19/37/47.5 -JM15 -Baf -W1 -Gp32+r100+fblue
echo 14 39 | gmt plot -Skmeca/3c -G100 -Wfaint
gmt end show
Here we are using a patern picked from the GMT pattern collection for the polygon fill
(but we could have used simply a constant color like for example -Glightblue). Run the script and we get.
You will be split into teams to work on an exercise:
- Discuss with your team which commands and options you would use
- Work together to make a script that generates the desired plot
- If you have any questions, ask on the Slack chatroom
Make a maps similar to this but with different colors and symbols
- Use different line styles to draw the itlian border
- Paint Italy with different colors and patterns
- Replace the beach ball with other symbols.
- Try to plot a different symbol for each of beach ball positions
Don't look at one solution.