Le 26 nov. 2020 =C3=A0 12:12, = Keith McKay <mckaymeister@gmail.com> a =C3=A9crit :
Thanks Fabrice = and Hans.
I now see I = can simplify some lines of the code:
pp :=3D ((xpart a[i])/cf*cm, (ypart a[i])/cf*cm); = now becomes pp:=3D a[i];
and
pp :=3D pp --- ((xpart a[i+1]/cf)*cm, = (ypart a[i+1])/cf*cm); now becomes pp :=3D pp --- a[i +1] ;

However I still have the problem in the calculation of xcoord = and ycoord which are used in the creation of path pp:

for = squig =3D 1 step 1 until 15:

xcoord :=3D = uniformdeviate(1) - 0.5 + (xpart a[i]/cf);

ycoord :=3D = uniformdeviate(1) - 0.5+ (ypart a[i]/cf);

pp :=3D pp .. {curl = 100}(xcoord*cm, ycoord*cm);

endfor;

I'm adding a small random amount = to the x and ypart of the pair a[i] to produce a path that is like a = squiggle (gribouiller in French, according to Google). I have to use cf = to convert to the x and yparts to centimeters since they seem to loose = the centimeter units on separation. I can't see anyway round this, or am = I missing something?

Thanks
Keith McKay

First = =C2=AB uniformdeviate(1) - 0.5 =C2=BB could be modified = to =C2=AB uniformdeviate(0.5)=C2=BB.

To add noise, you can use the randomized function = of Metafun. For exemple, you can write:

draw pp randomized 1cm ;

Fabrice.

On= 26/11/2020 15:19, Fabrice L wrote:
Hi keith,

Le 26 = nov. 2020 =C3=A0 10:09, Keith McKay <mckaymeister@gmail.com> a =C3=A9crit = :

Hi,
I have been using xpart and ypart to = extract these values from pairs of points in a path but I wasn't getting = the correct result. I was expecting:
pair (2cm, 11cm) to give xpart 2 and = ypart 11
However I was = getting:
pair (2cm, = 11cm) -> xpart 56.6929 and ypart 311.8096
After much head scratching and reading = the MetaPost and MetaFun manuals, I realised that the units of xpart or = ypart are in Postcript points or Big Points (bp), and 1 bp is 1/72 of an = inch, and thus to get the values of xpart or ypart in cm I would have to = use a correction factor. I had made the assumption that since the x and = ypart in the pair was in cm that the result would be in cm, but I see = now that this is not the case. Will I have to continue doing this or is = there some magic within MetaFun which takes account of the units in a = pair and outputs the result of x and ypart in the same units?
The MWE belows shows what I = have been doing.
Thanks
Keith McKay
%%% MWE %%%
\setuppapersize [A5, landscape][A4, = portrait]
\usecolors[crayola]
\starttext
\startMPpage
StartPage;
width :=3D = PaperWidth ; height :=3D PaperHeight ; unit :=3D cm ;
numeric squig;
pair a[]; a0 =3D (2cm,11cm); a1 =3D (4cm,10cm); a2 = =3D (6cm,9cm); a3 =3D (8cm,8cm);
show xpart a[0], ypart a[0]; %Example of result from = x and ypart before applying correction factor (cf) %
cf :=3D 72/2.54; %Converts points/in to = points/cm%
path pp;
for i =3D 0 step 1 until 3:
pp :=3D ((xpart a[i])/cf*cm, (ypart = a[i])/cf*cm);
for squig =3D 1 = step 1 until 15:
xcoord = :=3D uniformdeviate(1) - 0.5 + (xpart a[i]/cf);
ycoord :=3D uniformdeviate(1) - 0.5+ = (ypart a[i]/cf);
pp :=3D = pp .. {curl 100}(xcoord*cm, ycoord*cm);
endfor;
pp :=3D = pp --- cycle;
if i < 3 = :
pp :=3D pp --- ((xpart = a[i+1]/cf)*cm, (ypart a[i+1])/cf*cm);
fi;
f :=3D((1.4 - 0.6) * uniformdeviate(1)) + 0.8; % = Factor to lighten/darken colour %
draw pp withpen pencircle xscaled 0.5mm yscaled = .1mm rotated 45 withcolor (f[white,\MPcolor{BurntSienna}]);
endfor;
StopPage;
\stopMPpage
\stoptext
%%%%%%%%%%%%%%

MetaPost = (MetaFun) is taking care of everything regarding units. As you ave = discovered, everything is translated to a unique internal dimension. So = you can write:

a :=3D (1cm,2in) ;

with no problem. The =C2=AB cm = =C2=BB and =C2=AB in =C2=BB parts of the expression will become = numbers to translate this number on the right unit.
Fabrice.
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