Our first animation is not very ambitious: We wish to plot the sine function from 0-360° and take snap shots every 20°. To get a smooth curve we must sample the function much more frequently; we settle on 10 times more frequently than the frame spacing. We place a bright red circle at the leading edge of the curve, and as we move forward in time (here, angles) we dim the older circles to a dark red color. We add a label that indicates the current angle value. Once the 18 frames are completed we convert them to a single animated GIF file and write a plain HTML wrapper with a simple legend. Opening the HTML page anim01.html in the browser will display the animation.
#!/bin/sh # GMT ANIMATION 01 # # Purpose: Make web page with simple animated GIF of sine function # GMT progs: gmtset, gmtmath, psbasemap, pstext, psxy, ps2raster # Unix progs: awk, mkdir, rm, mv, echo, convert, cat # # 1. Initialization # 1a) Assign movie parameters . gmt_shell_functions.sh width=4i height=2i dpi=125 n_frames=18 name=`basename $0 '.sh'` # 1b) Do frame-independent calculations and setup angle_step=`gmtmath -Q 360 $n_frames DIV =` angle_inc=`gmtmath -Q $angle_step 10 DIV =` gmtset DOTS_PR_INCH $dpi psbasemap -R0/360/-1.2/1.6 -JX3.5i/1.65i -P -K -X0.35i -Y0.25i \ -Ba90g90f30:,-\\312:/a0.5f0.1g1WSne -Glightgreen \ --PAPER_MEDIA=Custom_${width}x${height} --ANNOT_FONT_SIZE=+9p > $$.map.ps # 2. Main frame loop mkdir -p $$ frame=0 while [ $frame -le $n_frames ]; do # Create file name using a name_##.tif format file=`gmt_set_framename $name $frame` cp -f $$.map.ps $$.ps angle=`gmtmath -Q $frame $angle_step MUL =` if [ $frame -gt 0 ]; then # First plot has no curves # Plot smooth blue curve and dark red dots at all angle steps so far gmtmath -T0/$angle/$angle_inc T SIND = $$.sin.d psxy -R -J -O -K -W1p,blue $$.sin.d >> $$.ps gmtmath -T0/$angle/$angle_step T SIND = $$.sin.d psxy -R -J -O -K -Sc0.1i -Gdarkred $$.sin.d >> $$.ps fi # Plot red dot at current angle and annotate sin=`gmtmath -Q $angle SIND =` echo $angle $sin | psxy -R -J -O -K -Sc0.1i -Gred >> $$.ps echo $angle | awk '{printf "0 1.6 14 0 1 LT a = %3.3d\n", $1}' \ | pstext -R -J -O -K -N -Dj0.1i/0.05i >> $$.ps psxy -R -J -O /dev/null >> $$.ps if [ $# -eq 0 ]; then mv $$.ps $name.ps gmt_cleanup .gmt gmt_abort "$0: First frame plotted to $name.ps" fi # RIP to TIFF at specified dpi ps2raster -E$dpi -Tt $$.ps mv -f $$.tif $$/$file.tif echo "Frame $file completed" frame=`gmt_set_framenext $frame` done # 3. Create animated GIF file and HTML for web page convert -delay 20 -loop 0 $$/*.tif $name.gif cat << EOF > $name.html <HTML> <TITLE>GMT Trigonometry: The sine movie</TITLE> <BODY bgcolor="#ffffff"> <CENTER> <H1>GMT Trigonometry: The sine movie</H1> <IMG src="$name.gif"> </CENTER> <HR> We demonstrate how the sine function <I>y = sin(a)</I> varies with <I>a</I> over the full 360-degree interval. We plot a bright red circle at each new angle, letting previous circles turn dark red. The underlying sine curve is sampled at 10 times the frame sampling rate in order to reproduce a smooth curve. Our animation uses Imagemagick's convert tool to make an animated GIF file with a 0.2 second pause between frames, set to repeat forever. <HR> <I>$name.sh: Created by $USER on `date`</I> </BODY> </HTML> EOF # 4. Clean up temporary files gmtset DOTS_PR_INCH 300 gmt_cleanup .gmt
Make sure you understand the purpose of all the steps in our script. In this case we did some trial-and-error to determine the exact values to use for the map projection, the region, the spacing around the frame, etc. so that the final result gave a reasonable layout. Do this planning on a single PostScript plot before running a lengthy animation script.