Thanks Taco! I understand much better now. I think it's best to leave the units out until the drawing stage as you suggest. Thanks again Keith McKay
On Fri, 27 Nov 2020, 08:30 Taco Hoekwater, <t...@elvenkind.com> wrote: > > > > On 26 Nov 2020, at 16:09, Keith McKay <mckaymeis...@gmail.com> wrote: > > > > 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 > > As explained by various people, Metapost does not have dimensions. All > lengths are implicit Postscript big points > (72/inch). Variables like “cm” just add a multiplication factor to your > expressions, at no point is a dimension stored inside Metapost. > > Your equation: > > a0 = (2cm,11cm) > > first expands into > > a0 = (2*28.34645,11*28.34645) > > because “cm” is a variable with a value (Its definition in plain.mp is > "cm = 28.34645”) > > Then, the two expressions in the a0 equation are resolved before the > assignment, so what you actually wrote at the statement level is > > a0 = (56.6929, 311.8096); > > At no point is there a “cm”-sized dimension. > > === > > Perhaps another option would be for you to do all your work without units, > e.g. > > a0 = (2,11) % assume scaling will happen later > > and then in the end do the drawing on a scaled path: > > draw (pp scaled cm) … > > as that may be less confusing? If the precision is an issue, you could > counter the loss of precision you could use implied millimeters instead of > centimeters. > > Best wishes, > Taco > > > > > > > ___________________________________________________________________________________ > If your question is of interest to others as well, please add an entry to > the Wiki! > > maillist : ntg-context@ntg.nl / > http://www.ntg.nl/mailman/listinfo/ntg-context > webpage : http://www.pragma-ade.nl / http://context.aanhet.net > archive : https://bitbucket.org/phg/context-mirror/commits/ > wiki : http://contextgarden.net > > ___________________________________________________________________________________ >
___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context webpage : http://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : http://contextgarden.net ___________________________________________________________________________________
