Rendering artifact for certain concave surface

[DaveInCaz]

I'm using https://www.ladybug.tools/spider-2020/spider-idf-viewer/v-2020-06-20/spider-idf-viewer.html

I have one surface which is rendering with what looks like an artifact included within the area of an external corner:

Here it is by itself:

BuildingSurface:Detailed,
  _main west_Floor22_{00077},             !- Name
  Floor,                                  !- Surface Type
  BW Std Slab Floor_{00011},              !- Construction Name
  Zone_unnamed space (2)_main west_{00227}, !- Zone Name
  Adiabatic,                              !- Outside Boundary Condition
  ,                                       !- Outside Boundary Condition Object
  NoSun,                                  !- Sun Exposure
  NoWind,                                 !- Wind Exposure
  ,                                       !- View Factor to Ground
  ,                                       !- Number of Vertices
  38.705, -36.617, 0,                     !- X,Y,Z Vertex 1 {m}
  27.735, -16.647, 0,                     !- X,Y,Z Vertex 2 {m}
  24.743, -16.647, 0,                     !- X,Y,Z Vertex 3 {m}
  29.883, -6.137, 0;                      !- X,Y,Z Vertex 4 {m}

Other concave shapes in the same model render OK.

Is this a problem with the input data? An issue in the viewer?

Let me know if I can add any other useful info... thanks

[DaveInCaz]

I just noticed, that floor surface has a matching roof surface of the same shape, which does not show the same artifact. Here are both of them:

BuildingSurface:Detailed,
  _main west_Roof19_{00074},              !- Name
  Roof,                                   !- Surface Type
  Medium Weight Roof_{00022},             !- Construction Name
  Zone_unnamed space (2)_{00305},         !- Zone Name
  Outdoors,                               !- Outside Boundary Condition
  ,                                       !- Outside Boundary Condition Object
  SunExposed,                             !- Sun Exposure
  WindExposed,                            !- Wind Exposure
  ,                                       !- View Factor to Ground
  ,                                       !- Number of Vertices
  29.883, -6.137, 3.657,                  !- X,Y,Z Vertex 1 {m}
  24.743, -16.647, 3.657,                 !- X,Y,Z Vertex 2 {m}
  27.735, -16.647, 3.657,                 !- X,Y,Z Vertex 3 {m}
  38.705, -36.617, 3.657;                 !- X,Y,Z Vertex 4 {m}

[mostaphaRoudsari]

This is most likely happening for a similar reason as this one: #16

[theo-armour]

@DaveInCaz

I will have a look