View source for Ps.map graph paper

== Creating graph paper with ps.map ==

The {{cmd|ps.map}} module is quite flexible. This example will demonstrate how to use it to create some graph paper and save it into a PostScript or PDF file ready for printing. With some slight tweaks you can make A3, Legal-sized, etc. paper with the grid resolution of your choosing.

This is not the most efficient method, but it's just a demonstration after all.

=== Background ===

Some useful numbers and facts to know before we start:

* PostScript's (and so PDF's) natural unit is the ''point''. As in a 10 point font. A point is 1/72 of an inch. So for PostScript tasks it is both common and easiest to work directly with inches.

* A sheet of A4 paper is 8.268" x 11.693". A sheet of Letter sized paper is 8.5" x 11".

* 25.4 mm = 1"

* The aspect ratio of metric paper sizes is length = width * sqrt(2).


==== Creating graph paper with a 1/4 inch grid ====

First create a new location using inches as the base unit.

Assuming you used the text-based interactive startup wizard:
* Create a new location
* [D] - Other projection
* Projection: eqc  (Plate Caree)
* No datum
* Ellipsoid: sphere
* Radius of Earth: just use the default
* Latitude, Longitude of center.. just set to 0.0
* Enter plural form of units [meters]: inches
* Enter conversion factor from inches to meters: 0.0254

* set region: 
: Here we will want to calculate the size of the grid canvas. It will be a little smaller than the paper size. So given the above dimensions Letter-sized paper with 1/2" margins on the sizes and 1" on the top and the bottom, the grid canvas will be 7.5" x 9". So set north=9, south=0, west=0, and east=7.5. Set the resolution to 0.25. The exact default region is not important, it's just to get us started.

<!--
(round down to nearest whole grid)
g.region  n=9 s=0 w=0 e=7.25 res=0.25

 a4 - 1/2" margins = 7.268 x 10.693" = 184.6 x 271.6022mm
 a4 - margins = 7.268 x 
   1/4" boxes: 7.268/.25 = 29.072 x 42.772 boxes
-->

Next start up GRASS in a new mapset in this new location.


While the {{cmd|d.grid}} command can be used multiple times at different grid distances, unfortunately ''ps.map'''s '''grid''' instuction can only be used once. You can use {{cmd|v.mkgrid}} to make a grid pattern though, so we'll use that to make the finer scale grid.

 v.mkgrid inch_grid grid=9,7 position=coor coor=0,0 box=1,1

 g.region -p # check that res=0.25; read rows,cols for grid option
 v.mkgrid quarter_inch_grid grid=36,30


===== On A4 paper =====

For A4 paper we'll use a 1/2" margin on the left and right, a 1" margin on the top, and a bit of a bigger margin on the bottom to leave room for a ruler.

So we are left with <tt>8.268" - (2 * 0.5") = 7.268"</tt> wide and <tt>11.693" - 1" - 1.5" = 9.193"</tt> tall. To maintain whole grid boxes we'll round this down to 7.25" x 9".

 g.region  n=9 s=0 w=0 e=7.25 res=0.25

And save it as a named region for future reference.
 g.region save=a4

With all that set up we can run ''ps.map'':

<source lang="bash">
ps.map out=quarter_inch_a4.ps << EOF

paper a4
  left 0.5
  right 0.5
  top 1.0
  bottom 1.5
  end
scale 1:1
grid 1
  color black
  width 0.5
  end
vareas quarter_inch_grid
  fcolor none
  color grey
  width 0.5
  end
scalebar s
  where 4.134 10.75
# 4.134 = width a4 / 2
  length 5
  segment 20
  numbers 4
  end
end

EOF
</source>


And convert to PostScript using the `ps2pdf` program that comes with {{wikipedia|Ghostscript}}:
 ps2pdf quarter_inch_a4.ps

===== On Letter paper =====

This is mostly the same, we just modify the margins a bit and the region to match.

 11" - margins = 9"
 8.5" - margins = 7.5"
 g.region n=9 e=7.5
 g.region save=letter
  # 1/4" wider

<source lang="bash">
ps.map out=quarter_inch_letter.ps << EOF

paper us-letter
  left 0.5
  right 0.5
  top 0.75
  bottom 1.25
  end
scale 1:1
grid 1
  color black
  width 0.5
  end
vareas quarter_inch_grid
  fcolor none
  color grey
  width 0.5
  end
scalebar s
  where 4.25 10.35
# 4.25 = width letter / 2
  length 5
  segment 20
  numbers 4
  end
end

EOF
</source>

Convert to PostScript:
 ps2pdf quarter_inch_letter.ps


#-------------------------------------------

# mm: create another location, but this time

Enter plural form of units [meters]: millimeters
Enter conversion factor from millimeters to meters: 0.001

set region: (round down to nearest whole grid)
#n=9*25.4 e=7.25*25.4
n=230  e=190 res=1



v.mkgrid cm_grid grid=23,19 position=coor coor=0,0 box=10,10

g.region -p # read rows,cols
# that adds up to a lot, so we shrink it internally
v.mkgrid mm_grid_raw grid=230,190
v.build.polylines in=mm_grid_raw out=mm_grid
g.remove vect=mm_grid_raw



# mm / A4
g.region n=230 e=180 s=0 w=0 res=1
g.region save=a4
# width grid: 180 mm / 2.54 = 7.087"
# ( width a4 - width grid ) / 2 = 0.59" margins
# 

ps.map out=mm_a4.ps << EOF
paper a4
  left 0.59
  right 0.59
  top 1.0
  bottom 1.5
  end
scale 1:1
grid 10
  color black
  width 0.5
  end
vareas mm_grid
  fcolor none
  color 180:180:180
  width 0.5
  end
scalebar s
  where 4.134 10.75
# 4.134 = width a4 / 2
  length 100
  segment 10
  numbers 2
  end
end
EOF

#convert to postscript
ps2pdf mm_a4.ps


#-------------------------------------------
# mm / Letter

g.region n=230 e=190 s=0 w=0 res=1
# width grid: 190 mm / 2.54 = 7.48"
# ( width letter - width grid ) / 2 = 0.51" margins
# 

ps.map out=mm_letter.ps << EOF
paper us-letter
  left 0.51
  right 0.51
  top 0.75
  bottom 1.25
  end
scale 1:1
grid 10
  color black
  width 0.5
  end
vareas mm_grid
  fcolor none
  color 180:180:180
  width 0.5
  end
scalebar s
  where 4.25 10.35
# 4.25 = width letter / 2
  length 100
  segment 10
  numbers 2
  end
end
EOF

#convert to postscript
ps2pdf mm_letter.ps






=== See also ===

* I'm pretty sure [[GMT]] has a graph paper demo, and I got the idea for this demo from them. (''link?'')


[[Category: ps.map]]