1
$\begingroup$

Code as simple as it is:

targetRegion = RegionUnion[Disk[{0, 0}], Disk[{1.8, 0}]];
edgeDistFn = RegionDistance[RegionBoundary@targetRegion]
pts = RandomPoint[targetRegion, {2, 2}];
pts // edgeDistFn

This should give distances of all points to the boundary, but works on neither 12.1.1 nor 12.2, with output like:

{{RegionDistance[
   RegionBoundary[
    BooleanRegion[#1 || #2 &, {Disk[{0, 0}], 
      Disk[{1.8, 0}]}]], {-0.4243129646, 0.5777295089}], 
  RegionDistance[
   RegionBoundary[
    BooleanRegion[#1 || #2 &, {Disk[{0, 0}], 
      Disk[{1.8, 
        0}]}]], {1.227762454, -0.3983038364}]}, {RegionDistance[
   RegionBoundary[
    BooleanRegion[#1 || #2 &, {Disk[{0, 0}], 
      Disk[{1.8, 0}]}]], {2.160377018, 0.6768344764}], 
  RegionDistance[
   RegionBoundary[
    BooleanRegion[#1 || #2 &, {Disk[{0, 0}], 
      Disk[{1.8, 0}]}]], {1.547838415, -0.00215747549}]}}

Is this a bug or an individual issue?

Despite @cvgmt's answer (a makeshift, inaccurate, and numerical solution), the reason why we need to discretize the region (in many cases, especially those where $\mathtt{Disk}$s, $\mathtt{Cone}$s, etc., are involved in $\mathtt{RegionUnion}$, $\mathtt{RegionIntersection}$, etc.) or most of the functions for region measurement will fail to work is still unclear.

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2
  • $\begingroup$ Don't use the bugs tag until other people have already confirmed that what you have is a bug. $\endgroup$
    – J. M.'s missing motivation ♦
    Commented Jan 22, 2021 at 3:21
  • $\begingroup$ @J.M. Get it. Thanks! :) $\endgroup$
    – SnzFor16Min
    Commented Jan 22, 2021 at 3:29

1 Answer 1

Reset to default
4
$\begingroup$

Updated

We also need DiscretizeRegion

SeedRandom[1];
targetRegion = 
  RegionUnion[Disk[{0, 0}], Disk[{1.8, 0}]] // DiscretizeRegion;
pts = RandomPoint[targetRegion, {2, 2}];
values = SignedRegionDistance[targetRegion][pts]
Show[targetRegion // Region, 
 Graphics[{PointSize[Large], Red, Point /@ pts, 
   MapThread[Circle, {pts, Abs@values}, 2]}]]

{{-0.599128, -0.208482}, {-0.425123, -0.179378}}

enter image description here

Original

It is recommended to use SignedRegionDistance.

SeedRandom[1];
targetRegion = RegionUnion[Disk[{0, 0}], Disk[{1.8, 0}]];
pts = RandomPoint[targetRegion, {2, 2}];
values = SignedRegionDistance[targetRegion][pts]
Show[targetRegion // Region, 
 Graphics[{PointSize[Large], Red, Point /@ pts, 
   MapThread[Circle, {pts, Abs@values}, 2]}]]

{{-0.238752, -1.27}, {-0.471944, -0.548317}}

enter image description here

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3
  • 1
    $\begingroup$ Thanks! This is accurate compared to RegionDistance[targetRegion // RegionBoundary // DiscretizeRegion][pts] — though I still wonder why RegionDistance hasn't done its job well. $\endgroup$
    – SnzFor16Min
    Commented Jan 22, 2021 at 3:33
  • $\begingroup$ @SneezeFor16Min It seems that there are something problem on my code , see the graphis. I think the problem come from the RegionUnion $\endgroup$
    – cvgmt
    Commented Jan 22, 2021 at 4:16
  • $\begingroup$ I see. Strange. Discretizing the boundary as I mentioned above, however, does give correct radii (albeit inaccurate): {{0.2361000112, 0.4516728083}, {0.4690868471, 0.5453502001}} $\endgroup$
    – SnzFor16Min
    Commented Jan 22, 2021 at 4:28

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