Art Spotlight: Holy Island Boat

In Art Spotlight, we invite Sketchfab artists to talk about one of their designs.

Hello, my name is Paul Dickinson and I am a web developer who lives and works in the beautiful county of North Yorkshire in the UK. I have always been interested in graphics ever since I started out in computing in the early 1980’s, but unfortunately, back then, there were not the opportunities, technology, and processing power that is so readily available today.

I have been a keen photographer for many years and am fascinated with learning new techniques and technologies. I love to draw people’s attention to detail that they would not normally see or notice in day to day life.

Just recently, I have discovered photogrammetry, and this is the perfect platform for me to utilise my photographic expertise as a way into 3D, and thus, taking my photography to an entirely new level.

Part of my current 3D ‘journey’ has brought me to the doors of Sketchfab where I have discovered a vibrant and, quite frankly, amazing community of 3D Modelers. This was all my dreams come true, as not only could I now realise my youthful dreams of dabbling in 3D, but also share my creations with a worldwide community. As an added bonus I have been able to receive feedback as to how I could improve my technique as well as hopefully inspire a few people along the way.

The software that I use comprises the following:

• Agisoft Photoscan
• Autodesk MeshMixer
• zBrush
• Meshlab
• ShaderMap

All of the above are a completely new set of tools for me to learn, and wow, what a steep learning curve it is proving to be. All I can say to people who are starting out in photogrammetry and 3D is, try not to be put off by all the terminology, attack the process methodically and draw on other people’s knowledge for navigating through this fascinating subject … it takes time, but patience will be rewarded.

Enough of my rambling, let’s move on to how I ‘attack’ a subject, what I look for, the equipment that I use, and, the steps that I take. I will use my Holy Island – Boat as the focus for this.

First off, my equipment …

• Sony RX100 M3
• Nikon D200 DSLR
• Monopod
• Wacom graphics tablet
• Turntable and 3 x 64 LED lighting units (for object scanning)

To be honest, you don’t really need a lot of equipment in order to have a go at photogrammetry. Anything from a mobile phone up to a pro DSLR camera will do. The emphasis here though, is the words ‘will do’. If you want good results from a scan, you will need good clean, well balanced images that pack a lot of detail – most mobile phones unfortunately won’t cut it in that respect, although they will yield acceptable results.

The hardware that I use at the moment is either a Sony RX100 M3 compact camera or a Nikon D200 DSLR with 35-70mm lens. The Sony is great if you want to travel light, the Nikon is great if you want more control over your scan/shots, particularly if you need to get closer to a distant subject. The Sony is 20 megapixel, and the Nikon is 10 megapixel .. in the scheme of things, the number of megapixels a camera has, has very little to do with the quality of your scan. There is absolutely no reason why a 6 or 7 megapixel camera couldn’t yield superior results to one of its bigger megapixel rivals. Quality of the glass and sensor are what counts – remember it’s not the size that matters, it’s what you do with it.

If you have the time, a tripod could be beneficial, but I have to admit, if you use a fast enough shutter speed, you more often than not, can get away without using one. One caveat to this though, is a monopod … one of these little babies can really help if the subject you are trying to capture is higher than yourself .. yes you do get funny looks, even comments, from people, but hey, we artists have to suffer these hardships in order to achieve perfection.

Secondly, my choice of subject …

I always try to look for interesting and detailed subjects, something that is unique and will interest others, or be an asset for others to use. When seeking subjects out, don’t be afraid of trying different sized studies, each offer different challenges in capturing. I have recently carried out a survey of Lindisfarne Castle on Holy Island and took a whopping 1400+ photos in the process (hmm, not sure how I am going to process this one) …. And then in contrast, some … erm, gravel (stop laughing .. no seriously … stop laughing) using only 8 photos .. so you can go as big and small as your imagination takes you !!

Thirdly, the workflow/technique that I use …

Please bear in mind that the following is just my approach, and that there are many other workflows you could adopt, you just have to find the one that suits you best. That said, there are some core rules that need to be considered.

1. Try to shoot on a bright, but cloudy day or using diffused light .. shadows and harsh highlights don’t want  to be ‘baked’ into your textures as it will look wrong in a lit 3D environment.
2. Shoot sharp i.e. I keep my aperture at f8 if I can, with the fastest shutter possible and the lowest ISO I can get away with.
3. Overlap your photos by at least 50%. This gives Agisoft Photoscan plenty of canvas to work with when trying to match points. Shooting this boat on Holy Island was a challenge as it had a lot of faces, corners and detail to capture both inside and out. Remember that a computer does not understand what it is looking at when processing the photos, so you have to ‘teach’ it the environment by covering every possible angle. I took 173 photos of this subject, and, with careful capture, I managed to achieve 100% photo match rate in Photoscan. This enabled Photoscan to re-create the scene pretty accurately. The downside of course is processing time … but all good things are worth waiting for.
4. If the subject I shoot has a great variation between light and dark .. I shoot to make sure that highlights and shadows do not clip (using the camera histogram) … the image may look a little underexposed, but this can be corrected in post … which leads to the next step.
5. Shoot in RAW if you can … RAW gives you the best chance to recover detail in the highlights and shadows alike in post processing.
6. Post process the RAW images in a tool such as Lightroom .. this will allow you to maximise the quality of the image (colour balance, sharpness (not too much), noise reduction, etc).
7. Start a new workflow in Photoscan using high/medium dense point cloud, aggressive or mild depth filtering and 8k texture size to maximise texture quality (I have also created some models with 16K textures). Bear in mind that high quality dense point clouds will hammer your machine (good for warming your room up in winter though ;-)) I only tend to use those for small subject areas.
8. After creating a mesh, and before texturing a model, I often run the mesh through Autodesk Meshmixer (see image below). This free software was suggested by a fellow Sketchfabber and it is a fantastic little tool for tidying your mesh up. As you can see in the image below, my poor old boat had quite a few fixes that need applying as depicted by the purple and blue pins … this is just the nature of photogrammetry though, and meshes always need a good clean!!
9. Depending on the subject and quality of scan, I may utilise zBrush to fix geometry and ‘quirks’ in the model.
   
   
10. Finally, I always create my models at the highest quality possible, then decimate the mesh accordingly depending on the audience/potential users of my models. When posting to Sketchfab I try to keep the poly count fairly high, thus allowing people to decimate to whatever level themselves, or if they so wish, use the higher poly count model from the get go. Even though my models on Sketchfab are relatively high in detail, they have still been decimated to a more acceptable level, so do not reflect the quality of the original scan.

The steps listed above are just the bare outline of my approach, and to be honest, each of those steps could be an entirely separate blog or tutorial as the depth of this subject is so great. Hopefully it provides enough information to get people going on their new adventure in photogrammetry and provide a few starting points to dig deeper.

Ending Notes

I would like to thank Sketchfab and their enthusiastic and talented community of modelers for A) Providing such a fantastic portal for 3D showcasing, and, B) Fantastic support and encouragement from staff and Sketchfabbers alike.

If you are interested in seeing more of my work, my Sketchfab Portfolio can be found here.

Keep up the good work everyone, feel free to contact me on the relevant model page if you have any questions, or in the comment box below.

I look forward to seeing more of your fantastic creations !!

Paul

Thanks, Paul!