Introduced artifacts when remeshing

[actondev]

Describe the bug I stumbled upon a weird behavior when remeshing, when some weird flipped face artifact was introduced. It seems that calling detect_boundary before remeshing (either with pmp::adaptive_remeshing or with pmp::uniform_remeshing) causes the issue.

To Reproduce Steps to reproduce the behavior:

const auto triangleEdgeLength = 0.5;
const auto algorithmIterations = 10;

std::filesystem::path in("input.obj");
pmp::read(mesh, in);
pmp::detect_boundary(mesh); // when this is commeted out, the issue is not present, however the remeshed mesh is not the desired one
pmp::uniform_remeshing(mesh, triangleEdgeLength, algorithmIterations, true);
std::filesystem::path out("remeshed.obj");
pmp::write(mesh, out);

The input.obj file:

# OBJ export from PMP
v -0.1982631236 3.4977140427 0.0000000000
v -1.3179311752 -1.3247808218 0.0000000000
v -0.3942996562 -2.1346323490 0.0000000000
v -0.8907890916 -1.5538849831 0.0000000000
v 1.6485068798 -2.1434488297 0.0000000000
v -1.0580925941 -1.0284365416 0.0000000000
v 2.0331587791 -0.4867242575 0.0000000000
v 0.8612220883 0.2289074957 0.0000000000
v 0.7864076495 1.0752063990 0.0000000000
v -0.6645965576 -0.5796559453 0.0000000000
v -0.6070595980 0.9520211816 0.0000000000
v -0.1982631236 3.4977140427 0.0000000000
f 11//11 1//1 2//2
f 2//2 3//3 4//4
f 4//4 5//5 6//6
f 6//6 7//7 8//8
f 8//8 9//9 10//10
f 10//10 11//11 2//2
f 2//2 4//4 6//6
f 6//6 8//8 10//10
f 10//10 2//2 6//6

The remeshed.obj file with the face artifact

``` # OBJ export from PMP v -0.1982631236 3.4977140427 0.0000000000 v -1.3179311752 -1.3247808218 0.0000000000 v -0.3942996562 -2.1346323490 0.0000000000 v -0.8907890916 -1.5538849831 0.0000000000 v 1.6485068798 -2.1434488297 0.0000000000 v -1.0580925941 -1.0284365416 0.0000000000 v 2.0331587791 -0.4867242575 0.0000000000 v 0.8612220883 0.2289074957 0.0000000000 v 0.7864076495 1.0752063990 0.0000000000 v -0.6645965576 -0.5796559453 0.0000000000 v -0.6070595980 0.9520211816 0.0000000000 v -0.1982631236 3.4977140427 0.0000000000 v -0.4026613533 2.2248675823 0.0000000000 v -0.7580971718 1.0864665508 0.0000000000 v 0.1011266708 -0.8252944350 0.0000000000 v -0.8561154008 -1.7297065258 0.0000000000 v -0.6425443888 -1.8442586660 0.0000000000 v 0.3788588941 -1.8486669064 0.0000000000 v 0.2952071428 -1.5859427452 0.0000000000 v 0.4875330925 -0.7575803995 0.0000000000 v 1.4471904039 -0.1289083809 0.0000000000 v 0.1551957279 -0.1203270555 0.0000000000 v 0.8238148689 0.6520569324 0.0000000000 v 0.0609055459 0.2477752268 0.0000000000 v 0.6335320473 -1.7253192663 0.0000000000 v -0.6358280778 0.1861826181 0.0000000000 v -0.6181386709 1.6892784834 0.0000000000 v -0.3004622459 2.8612909317 0.0000000000 v -1.0380141735 -0.1191571355 0.0000000000 v -0.1212951839 -0.5088999867 0.0000000000 v 1.0136828423 -1.9960578680 0.0000000000 v -0.3814427257 -1.3071897030 0.0000000000 v 1.2603459358 -0.6221523285 0.0000000000 v 1.1542062759 0.0499995574 0.0000000000 v 0.8739395142 -0.6898663640 0.0000000000 v -0.3018454909 -0.1659403592 0.0000000000 v -0.0431177914 -1.4465662241 0.0000000000 v -0.6214438677 0.5691019297 0.0000000000 v -0.5048604608 1.5884443521 0.0000000000 v -0.8980556726 0.4836547077 0.0000000000 v -0.4781801403 2.2920904160 0.0000000000 v -0.6716861725 -0.9607225060 0.0000000000 v 1.3101819754 -2.0040721893 0.0000000000 v -0.3382216394 2.8949022293 0.0000000000 v -0.2559651136 -1.7012759447 0.0000000000 v 1.6467523575 -0.5544382930 0.0000000000 v 0.9718570113 -1.8646957874 0.0000000000 v -0.2852797508 -0.8930084705 0.0000000000 v 0.7136108875 -0.3941425681 0.0000000000 v 1.7401745319 -0.3078163266 0.0000000000 v 1.0928871632 -0.3541852534 0.0000000000 v 0.5781729817 -0.0717795715 0.0000000000 v 0.3110318184 -0.4487698972 0.0000000000 v -0.6502122879 -0.1967366636 0.0000000000 v 0.4236565828 0.6614907980 0.0000000000 v -0.7197676897 -1.1678130627 0.0000000000 v -1.1779726744 -0.7219690084 0.0000000000 v 0.4780529737 0.2736637592 0.0000000000 f 54//54 29//29 57//57 f 4//4 16//16 17//17 f 56//56 6//6 2//2 f 34//34 8//8 52//52 f 36//36 10//10 30//30 f 11//11 40//40 38//38 f 56//56 2//2 16//16 f 39//39 27//27 14//14 f 55//55 24//24 58//58 f 22//22 30//30 53//53 f 44//44 28//28 1//1 f 52//52 53//53 49//49 f 42//42 48//48 10//10 f 16//16 4//4 56//56 f 3//3 17//17 16//16 f 48//48 15//15 30//30 f 43//43 31//31 5//5 f 53//53 52//52 22//22 f 7//7 50//50 46//46 f 52//52 49//49 34//34 f 47//47 25//25 18//18 f 58//58 8//8 23//23 f 55//55 23//23 9//9 f 45//45 37//37 32//32 f 27//27 13//13 41//41 f 57//57 42//42 10//10 f 2//2 6//6 57//57 f 14//14 11//11 39//39 f 8//8 58//58 52//52 f 30//30 22//22 36//36 f 48//48 30//30 10//10 f 26//26 40//40 29//29 f 49//49 51//51 34//34 f 19//19 37//37 45//45 f 35//35 51//51 49//49 f 51//51 35//35 33//33 f 53//53 30//30 15//15 f 47//47 18//18 31//31 f 11//11 14//14 40//40 f 41//41 13//13 28//28 f 22//22 52//52 58//58 f 26//26 38//38 40//40 f 36//36 22//22 24//24 f 27//27 39//39 13//13 f 10//10 54//54 57//57 f 31//31 43//43 47//47 f 56//56 4//4 32//32 f 32//32 4//4 45//45 f 28//28 44//44 41//41 f 33//33 46//46 50//50 f 57//57 6//6 42//42 f 29//29 54//54 26//26 f 58//58 24//24 22//22 f 45//45 18//18 19//19 f 55//55 58//58 23//23 f 19//19 18//18 25//25 f 15//15 20//20 53//53 f 20//20 49//49 53//53 f 49//49 20//20 35//35 f 33//33 50//50 21//21 f 21//21 51//51 33//33 f 34//34 51//51 21//21 ```

Expected behavior No new faces should be introduced and definitely not flipped faces!

Screenshots From left to right: the input mesh, remeshed without the detect_boundary call, remeshed with detect_boundary: you can notice the face artifact int red (it's also a flipped face with opposite normal)

Close up of the face artifact:

Environment (please complete the following information):

• OS: macOS
• Compiler:
  • Apple clang version 14.0.3 (clang-1403.0.22.14.1)
  • Target: arm64-apple-darwin22.4.0
  • Thread model: posix
• Build type: Release

[dsieger]

Thanks for reporting, I could reproduce the issue. Might be something with the tangential smoothing. I'll look into it. Quick workaround for the concrete case: try a smaller edge length (0.4 seems fine).

[actondev]

Just FYI, I was trying with latest main branch b0cc214c94736162fb36392cc4b80085e0d12f20 (because I saw some commits about remeshing) but the issue is still there