Can't create fat arrows with modern psvelo / velo

Q&A
1

The ‘classic’ style of psvelo has a nice option for specifying arrow width. For example, here is how I create a ‘fat’ arrow with a black outline all the way around it:

echo "0 0 1 0 0 0 0" |gmt psvelo -JX5i -Rg -W1p -L -Se3/0/1 -A0.15/0.8/0.2 -Gred > test_classic.ps
gmt psconvert -A1p -Tf test_classic.ps
open test_classic.pdf

I can’t find a way to do the same thing in ‘modern’ mode, because the GMT4-era options for -A ( −A Arrow_width/Head_length/Head_width) are no longer allowed. Now I must use the modern method that has no option for body width. I can control the head width/shape, but not the width of the main body except by making the outline pen thick (+p) - but then I lose the nice thin black outline and it just becomes a black arrow. But I figure it must be possible, somehow. How to fix this ‘modern’ code (below) to look like the classic case above?

gmt begin
gmt figure test_modern pdf A1p
echo "0 0 1 0 0 0 0" |gmt psvelo -JX5i -Rg -W1p -L -Se3/0/1 -A20p+e+gred+h0.5
gmt end
open test_modern.pdf
2

See +a for setting the apex angle [30 degrees I think]

3

The modern options are nicer for setting the head properties, yes, but I can’t figure out how to widen the body (i.e. the stem) of the arrow while keeping an outline around the whole thing.

4

I see. No, the old-style -A is still there for those who insists. It just never occurred to us (!) that anyone would prefer the old polygon Cartesian arrows… We added them back to psxy (and never removed them from velo I think). So your old-style -A should still work - if not then please give a small example that fails. But I think geographic vectors should be great circle lines with arrow heads and not Cartesian polygons. I just looked and both the man pages for psxy and velo explains the old GMT 4 arrow format at the end.

5

Thanks, glad to know it is still intended to be available and not deprecated! I can’t get it to work with velo though, GMT throws the error 0.2/1/0.3 not a valid number. Minimal example that fails:

gmt begin
gmt figure test_modern pdf A1p
echo "0 0 1 0 0 0 0" |gmt velo -JX5i -Rg -W1p -L -Se3/0/1 -A0.2/1/0.3
gmt end
open test_modern.pdf

The man page discussion in velo appears copied from psxy (it mentions -Sv|V). This arrow style does still work for me in psxy but I need the error ellipses provided by velo.

6

Funny, if I run your example as a one liner (no quotes of echo args on Windows), it works fine

echo 0 0 1 0 0 0 0 | gmt velo -JX5i -Rg -W1p -L -Se3/0/1 -A0.2/1/0.3 -png lixo
7

Hi
the new -A options on arrowhead are fine. Thanks a lot !!
On the other hand I cannot increase the width of the arrow (with -W) without
simultaneously increasing the pen width of the error ellipse.
Attached example.
Maybe separate pen parameters for the ellipse ?
happy new year
best
Nicola

echo 0 0 1 0 0.1 0.1 0 | gmt velo -JX5i -Rg -W3p -L -Se1/0.95/1 -A15p+g0+e+h0.5 -png lixo

8

Did you try adding +ppen to the option?

9

Use -L(your width),(your color). Otherwise those in -W will be used

10

For those attached to the past, do you know how to make it work in Pygmt?

11

No, but someone from the PyGMT team will eventually get back to you - holiday in the US this long weekend.