[GRASS-dev] Getting a dotted line in ps.map - Style mechanism

GRASS GRASS developer
1

Hello,

I wonder how can I obtain a dotted linestyle with ps.map. Using the
style parameter with a 1010 value, I only get a dashed line. What
controls the length of the dashes? From the ps.map man-page (6.3.0) I
really did not fully understand the mechanism of the 'style'
parameter. Moreover, the example of the style parameter reported in
the vlines section of the manual with '0-9' value, rises up an error:

ERROR: style 0-9 : illegal line style (vlines)

Any help/suggestions will be appreciated.

Regards,

Alessandro

--
Alessandro Frigeri, PhD

2

Alessandro Frigeri wrote:

I wonder how can I obtain a dotted linestyle with ps.map.
Using the style parameter with a 1010 value, I only get a dashed
line. What controls the length of the dashes? From the ps.map
man-page (6.3.0) I really did not fully understand the mechanism of
the 'style' parameter.

sorry, the documentation did not match the code very well.
(ie either the docs or the code is buggy, I am not really sure which)

try like:

# spearfish dataset
ps.map out=test.ps << EOF
vlines roads
  style 011111111
  where label ~ 'highway'
  width 0.5
  label Highways
  end
end
EOF

The first block is draw, the second block is don't draw. So with a single
zero followed by lots of ones it draws a little then skips a lot making a
dotted line.

Moreover, the example of the style parameter reported in the vlines
section of the manual with '0-9' value, rises up an error:

ERROR: style 0-9 : illegal line style (vlines)

"0-9" just means some value in the range of zero to nine. Forget about
that, just use 0s and 1s. Any non-zero number will be treated as a one.

I've just updated the man page in SVN to make things clearer:
  http://trac.osgeo.org/grass/changeset/32537

although I am not sure if the current way is as-intended or a bug.
intuitively I'd guess that 0 should be don't draw and 1 should be draw,
but alas..

devels see also the PostScript 'setdash' command usage and new debug messages:
  http://www.capcode.de/help/setdash

Hamish

3

Hi Hamish,

thanks for the hint. Now it is more clear to me how the style
parameter works (are we sure to leave that 0 means to stroke and 1 not
to stroke the line?).

Now I will try to understand how is defined the spacing between 0s and
1s, if it is scaled to the linewidth or not; I have not do it yet,
but looking at the code will surely help.

Then I've found a postscript operator it can be useful to obtain -real
dots- in a dotted line. The operator is called setlinecap and it sets
the look of the ends of the lines, the argument can be:
0) butt caps
1) round caps
2) extended butt caps

So an idea can be to introduce a new parameter in the vlines section
as e.g. linecap with the three options butt round and extbutt.

Regards,

Alessandro

2008/8/5 Hamish <hamish_b@yahoo.com>:

Alessandro Frigeri wrote:

I wonder how can I obtain a dotted linestyle with ps.map.
Using the style parameter with a 1010 value, I only get a dashed
line. What controls the length of the dashes? From the ps.map
man-page (6.3.0) I really did not fully understand the mechanism of
the 'style' parameter.

sorry, the documentation did not match the code very well.
(ie either the docs or the code is buggy, I am not really sure which)

try like:

# spearfish dataset
ps.map out=test.ps << EOF
vlines roads
style 011111111
where label ~ 'highway'
width 0.5
label Highways
end
end
EOF

The first block is draw, the second block is don't draw. So with a single
zero followed by lots of ones it draws a little then skips a lot making a
dotted line.

Moreover, the example of the style parameter reported in the vlines
section of the manual with '0-9' value, rises up an error:

ERROR: style 0-9 : illegal line style (vlines)

"0-9" just means some value in the range of zero to nine. Forget about
that, just use 0s and 1s. Any non-zero number will be treated as a one.

I've just updated the man page in SVN to make things clearer:
http://trac.osgeo.org/grass/changeset/32537

although I am not sure if the current way is as-intended or a bug.
intuitively I'd guess that 0 should be don't draw and 1 should be draw,
but alas..

devels see also the PostScript 'setdash' command usage and new debug messages:
http://www.capcode.de/help/setdash

Hamish

--
Alessandro Frigeri, PhD