[Photogrammetry] Architectural digital archive #3 Post-processing

I am Ryu Lilea (Ryu Fujiwara@lileaLab) who created Zeniarai Benten VR.

In the previous article, I wrote about ‘PC system requirement / 3DF Zephyr’.
This time I will write about ‘Post-processing’, summarizing how to adjust the generated 3D model.

※You can taste the VR space from here:

Themes in this series

Post-processing

I will explain how to adjust the model with a DCC tool (CG software).
※This time I use CINEMA4D.

Combine the divided parts

This time I generated the model with the division processing, so I need to combine the parts.

If there is a difference in height, there will be a gap between the parts. In that case, you need to correct it with an FDD tool (a tool to transform objects). I don’t go into the details of how to use this tool. Basically, transform the parts to match their ends as follows.

ZeniaraiBentenVR_03_FFD_01
※There is a gap.

ZeniaraiBentenVR_03_FFD_02
※Transform only the stairs and slope by using FFD tool (which is shown as purple wireframe).

ZeniaraiBentenVR_03_FFD_03
※ How it looks after adjuting the positions 

Correct the broken parts

Photogrammetry cannot reproduce reflection and transparency exactly, so the shape would break down or have holes. For Zeniarai Benten VR, I corrected the broken parts according to the type of problems:

  • Move vertices to fill the gap.
  • Place a flat object to fill the gap.
  • Hide by trees
  • Block the path

Move vertices to fill the gap

It’s the easiest way. For a small hole, you can fill it by moving the vertices of polygons.

Place a flat object to fill the gap

When shooting the photos for Zeniarai Benten VR, the roof was wet because it was drizzling. Therefore, the roof doesn’t have its surface generated due to the reflection.ZeniaraiBentenVR_03_Roof01
※There is a large hole in the roof.

For this kind of a major problem, make up new polygons with textures.

ZeniaraiBentenVR_03_Roof02
※Correct by adding the polygons with textures.

The following is an example of correcting the ground in the same way.

ZeniaraiBentenVR_03_Ground_01
※The texture of the stone-paved road is poor due to the lack of photos, and the asphalt floor has not been generated.

ZeniaraiBentenVR_03_Ground_02
※Prepare the texture.

ZeniaraiBentenVR_03_Ground_03
※ The state after the correction.

This ‘replacing the ground’ approach is useful even if the model is not broken. Photogrammetry costs a number of polygons because it converts a flat floor into fine meshes. So, you can save polygons by replacing the floor with a flat object.

Hide by trees

The northern part of Zeniarai Benten is elevated and all the photo have been taken at eye level. So, it gives a bird’s-eye view, highlighting the problematic parts. Because it’s not realistic to correct all these problems, I hid them by placing trees in front.

ZeniaraiBentenVR_03_Blindfold_01
※The problematic parts are widely visible

ZeniaraiBentenVR_03_Blindfold_02
※I hid them by placing trees (In reality, there are a lot of trees, so this correction looks natural).

Make the broken parts not noticeable

The site is surrounded by cliffs. But, Photogrammetry didn’t cover the top part of them, so it left a fairly visible boundary. I made it less visible by placing trees on it. You can make trees blend with the cliff by matching the colour tone and brightness of trees with the colour of the cliff.

ZeniaraiBentenVR_03_Cliff_01
※The upper part of the cliff is cut off unnaturally.

ZeniaraiBentenVR_03_Cliff_02
※Place the trees with its brightness and saturation adjusted to the colour of the trees, to make the boundary less noticeable.

Block the path to the broken part

For an excessively broken part, block the path to it.ZeniaraiBentenVR_03_deadend

The shown above is a cul-de-sac behind ‘Ryujin-Sui Mikuji’. It’s too narrow and dark to take decent photos. So, the model breaks down excessively. However, there are no attractive things, so I simply blocked the path by placing a transparent wall around the traffic cone.
(We will set up a collider there when converting into VR).

Adjust textures

The inside of the tunnel was generated from the video, and the exit of the tunnel was generated from the still image. But, those have been taken at different times, so the brightness of the floor has a gap at the boundary.

ZeniaraiBentenVR_03_Texture_04

Adjust the texture to correct this gap.

The following image is the texture generated by 3DF Zephyr.

ZeniaraiBentenVR_03_Texture_01

In order to correct the gap, I want to change the pale-blue area at the tunnel exit into grey. But it’s a bit painful to select the target area as it’s scattered all over the texture. So, I adjusted the texture with Photoshop as follows.

ZeniaraiBentenVR_03_Texture_02

Select ‘Selective Color’ and set ‘Preset’ to ‘Blues’.

ZeniaraiBentenVR_03_Texture_03

Then select ‘Hue/Saturation’ and decrease the ‘Saturation’ and ‘Lightness’ for Blues and Cyans.

ZeniaraiBentenVR_03_Texture_06

Now, only the pale-blue area has been adjusted and blended with the surroundings.

Prepare signboards and information boards separately

Prepare the separate textures for signboards and information boards to improve their visibility and readability.

ZeniaraiBentenVR_03_Billboard_03

Attach these textures to flat objects and place them.

ZeniaraiBentenVR_03_Billboard_02
※Examples of signboard and information board – The model was distorted and the characters collapsed, so they were unreadable.

 ZeniaraiBentenVR_03_Billboard_01
※I placed the flat objects with the high-resolution textures attached.

As seen above, in addition to the photos for Photogrammetry itself, it is a good practice to take close-up photos to make readable textures.

The theme in the next article

Thank you for reading through this tutorial.
If you have any questions, please don’t hesitate to contact via Twitter (Reply or Direct Message).

In the next article, I will write about ‘Conversion into VR’, summarizing the tips to make the model into a VR content.

Written by Ryu Fujiwara (Ryu lilea)