ImageMagick: redraw a text without "-draw" for only outward stroke - imagemagick

Question

I try to create a text image with ImageMagick, where is the stroke expands only outward. I found a solution, where I should use the "-draw" command, but with it I would need the size of my image, but I don't know it in advance.
The command below should be upgrated. Somehow I would need to draw the text again on it, without strokewidth:
convert -background none -fill white -pointsize 100 -stroke red \
-strokewidth 20 label:text stroke.png
#leu's solution almost good, but the positioning of the new text isn't in the good position. My result was that above, and I don't know, where I took a mistake:

Answer 1

My suggestion: combine label:"Some text" with -annotate "Some text". Like this:
#myfont="Arial-Black-Standard"
#myfont="Tahoma"
#offset="-0-0"
#offset="-20-10"
#offset="-30-10"
#offset="-10+10"
myfont="Tahoma"
offset="+10+10"
convert -respect-parentheses \
\( \
-font "${myfont}" \
-pointsize 180 \
-strokewidth 18 \
-fill blue \
-stroke blue \
-background none \
label:"Test text" \
\) \
-gravity center \
-font "${myfont}" \
-pointsize 180 \
-fill white \
-annotate "${offset}" "Test text" \
result${offset}.png
Play with the offset=... variable (also with the point sizes and stroke widths) to get closer to what you want. Here are some of my results:
However, like #MarkSetchell, I do not fully comprehend what you want to achieve. An explanation of what you mean by "outward stroke" that I do understand is missing...

Answer 2

yes: draw the same text onto your pic - maybe by piping output of your command to another convert
convert -background none -fill white -pointsize 100 -stroke red \
-strokewidth 20 label:text png:- \
| convert -fill white -pointsize 100 -stroke none \
-draw 'text 10,82 "text"' - stroke.png
the trick is to correctly place the second string. x-position is half the strokewidth, but y-position seems to be font- and pointsize-dependant. My approach was to first place both strings over each other when strokewidth was set to 0:
convert -background none -fill white -pointsize 100 -stroke red \
-strokewidth 0 label:text png:- \
| convert -fill white -pointsize 100 -stroke none \
-draw 'text 0,72 "text"' - stroke.png
then you have to add half the strokewidth to this y-position as well.
a bit of trial-and-error to get the correct y-position, but it seems to work for any string.
== edit ==
of course, we don't need to do trial-and-error. But instead we can use ImageMagick's power. Just perform the following steps (in this example within Bash):
#!/bin/bash
# read text from command line (or use "Test Text")
text=${1:-"Test Text"}
# strokewidth
sw=20
# pointsize
ps=120
# font
font=Arial
# result file
result="stroke.png"
# do some calc
sw_half=$(expr $sw / 2)
convert -background none -font $font -fill white -pointsize $ps -stroke red -strokewidth $sw label:"$text" $result
convert -background none -font $font -fill white -pointsize $ps -stroke none label:"$text" png:- | composite -geometry +${sw_half}+${sw_half} - $result $result
You can get the list of fonts available on your system by
convert -list font
The idea is the same as above: draw the text twice and draw one onto the other while using an offset of half the strokewidth.
The results all look like the following