TextureMesh can generate .ply, but failed generating .obj.

[citystrawman]

Describe the bug
for TextureMesh, I tried both generate .ply as well as .obj, but it can only generate .ply, failed generating .obj.

To Reproduce
Steps to reproduce the behavior:

1. the log and command of generating .ply:

Command line: TextureMesh 
--input-file $WorkingFolder\database\model_dense.mvs 
-m $WorkingFolder\database\model_dense_mesh.ply 
--working-folder $WorkingFolder\database\dense 
--output-file $WorkingFolder\model_texture.mvs
......
01:15:17 [App     ] Camera model loaded: platform 32; camera  0; f 0.790x0.787; poses 1
01:15:17 [App     ] Scene loaded from interface format (75ms):
	33 images (33 calibrated) with a total of 95.93 MPixels (2.91 MPixels/image)
	21171 points, 0 vertices, 0 faces
01:15:17 [App     ] Mesh loaded: 1820681 vertices, 3641031 faces (236ms)
01:17:42 [App     ] Assigning the best view to each face completed: 3641031 faces (2m25s22ms)
01:18:22 [App     ] Generating texture atlas and image completed: 41345 patches, 8192 image size, 2 textures (39s982ms)
01:18:23 [App     ] Mesh texturing completed: 1820681 vertices, 3641031 faces (3m5s96ms)
01:18:42 [App     ] Mesh saved: 1820681 vertices, 3641031 faces (19s160ms)
01:18:42 [App     ] MEMORYINFO: {
01:18:42 [App     ] 	PageFaultCount 8835373
01:18:42 [App     ] 	PeakWorkingSetSize 9.66GB
01:18:42 [App     ] 	WorkingSetSize 172.59MB
01:18:42 [App     ] 	QuotaPeakPagedPoolUsage 390.95KB
01:18:42 [App     ] 	QuotaPagedPoolUsage 366.20KB
01:18:42 [App     ] 	QuotaPeakNonPagedPoolUsage 127.84KB
01:18:42 [App     ] 	QuotaNonPagedPoolUsage 82.42KB
01:18:42 [App     ] 	PagefileUsage 263.91MB
01:18:42 [App     ] 	PeakPagefileUsage 9.95GB
01:18:42 [App     ] } ENDINFO

2. the log and command of generating .obj:

Command line: TextureMesh 
--export-type obj 
--input-file $WorkingFolder\database\model_dense.mvs 
-m $WorkingFolder\database\model_dense_mesh.obj 
--working-folder $WorkingFolderdatabase\dense
--output-file $WorkingFolder\model_texture.mvs

......
12:19:38 [App     ] Camera model loaded: platform 32; camera  0; f 0.790x0.787; poses 1
12:19:38 [App     ] Scene loaded from interface format (75ms):
	33 images (33 calibrated) with a total of 95.93 MPixels (2.91 MPixels/image)
	21171 points, 0 vertices, 0 faces
12:19:38 [App     ] error: invalid OBJ file
12:19:38 [App     ] error: cannot load mesh file
12:19:38 [App     ] MEMORYINFO: {
12:19:38 [App     ] 	PageFaultCount 29891
12:19:38 [App     ] 	PeakWorkingSetSize 113.55MB
12:19:38 [App     ] 	WorkingSetSize 109.27MB
12:19:38 [App     ] 	QuotaPeakPagedPoolUsage 353.32KB
12:19:38 [App     ] 	QuotaPagedPoolUsage 353.24KB
12:19:38 [App     ] 	QuotaPeakNonPagedPoolUsage 21.54KB
12:19:38 [App     ] 	QuotaNonPagedPoolUsage 21.46KB
12:19:38 [App     ] 	PagefileUsage 191.07MB
12:19:38 [App     ] 	PeakPagefileUsage 194.76MB
12:19:38 [App     ] } ENDINFO

From the log I can see that the error said "invalid OBJ file", I am not sure what is wrong with it.

BTW I am not clear what is the difference between parameter --mesh-file and --output-file

[5VK8Y]

-m/--mesh-file loads a mesh, overwriting existing mesh.
-o/--output-file filename for storing the mesh. Suffix added to archive/mesh file.