Issues with lines in anmiation 04

Q&A
1

I made a modified version of animation 04.

I add this command:

gmt coast -N1/thinner -N2/thinner,dashed

I noticed two things on the lines:

  1. It seems to me that the width of the line changes. They are wither in far sector of the frame. Is it just my impression? Is it a bug? What can I do_
  2. The dashed lines moves as the movie run. Is it possible to fixed the segments of the lines?

Full script:

# 1. Create files needed in the loop
cat << 'EOF' > pre.sh
gmt begin
	gmt project -C-68.304444/-57.807222 -E-65.6/-22.105556 -G5 -Q > flight_path.txt
	gmt image 1.jpg -D0/0+w24c -X0 -Y0
gmt end
EOF
cat << 'EOF' > main.sh
gmt begin
	gmt grdimage -JG${MOVIE_COL0}/${MOVIE_COL1}/${MOVIE_WIDTH}+du+z160+a3+t55+v36 -Rg @earth_night -Xc -Y-5c
#	gmt coast -N1/thinner -N2/thinner,dashed
gmt end
EOF
# 3. Run the movie
gmt movie main.sh -Chd -Nanim04_space_night -Tflight_path.txt -Sbpre.sh -H2 -Vi -Ml,png -Fmp4
2

No, it is not possible to control this since the total length of the projected boundary changes with the view point. One would some have need to compute the length of the projected boundary (in cm), then do math to determine what is a dash spacing that would keep the number of dashes the same. Not easy. I would bypass the problem with a solid line instead.

3

Thanks Paul. Is it the same about the width of the line?

4

Hm, should not be. The line is not projected onto the surface of the earth (it is not a skinny polygon) so its thickness should be constant across all, but perhaps it may appear to the viewer that it changes when the perspective for all other things change.