Digitizing Elmo (Windows)

Just today I participated in the first step of a collaborative project between departments at Kingston which involved a live demo – the product was a point cloud of of an Elmo/Monster toy as shown below. Here I’ll just go through the steps involved in the cloud generation, so hopefully readers can replicate it themselves!

IMG_3858.JPG

Our test subject

  • Images

For generating the data, I used my Canon 500D with a 50mm EF2 lens, so nothing overly fancy. I started by putting the subject on a raised platform in order to minimize the effect of reconstructing the ground, and used an aperture of f/5 or so to ensure the subject was in focus, but that the ground was not. A good example of precautions to take when dealing with low-texture objects is introduced in this blog post, but can often be limited by the amount of RAM in a computer. As I was somewhat time limited, I decided to forgo the accuracy of using a tripod and so used a fast shutter speed (1/30 s) with an ISO of 400 to compensate, and generally just tried to get a reasonable amount of coverage on the subject. I took some other images with a wider aperture (f/2) and faster shutter speed (1/50 s) also. I threw a few paintbrushes into the scene to generate a bit more texture.

The test dataset (Some images are very poor I’m aware!) can be downloaded here.

  • Model building

For convenience, Agisoft Photoscan (There’s a free 30-day trial) was used to build the model, though other open source alternatives exist, such as VisualSFM or MicMac. I’ve included a short slideshow on what the exact steps are in Photoscan below to hopefully make it easy to follow!

This slideshow requires JavaScript.

  • Level/denoise in CloudCompare

CloudCompare is an open source point cloud editing software available here. Because our model is exported without any coordinate system, it can’t tell up from down, but we can fix this! In CloudCompare we can use the leveling tool to quickly orient the model so it’s a bit easier to view. Another useful tool is the ‘Statistical outlier removal filter’ in tools-> clean-> SOR filter, though we’ll skip it in this case.

This slideshow requires JavaScript.

  • Preparing to upload

Potree is a free point cloud viewer which can be used to host datasets online. Here we’ll just used in it’s most basic form to get a minimum example out. This section gets a bit hairier than the others but hopefully it’s intelligible. We’ll need to download and unzip both the potree converter and potree in the same directory, making a new subdirectory for each; ‘Converter’ and ‘Potree’. Next we’ll add the model we saved from CloudCompare to the potree converter directory, renaming it to ‘model.las’. Then we’ll follow the slides below!

Note – the command for the fourth slide is ‘PotreeConverter.exe model.las -o ../../Potree/potree-1.3/model_out –generate-page model’

This slideshow requires JavaScript.

  • Upload to the web

While there’s instructions for Kingston Students on how to upload web pages, this is a general skill that is good to have. We use FileZilla FTP to log in to our server, and the idea is to upload the entirety of the Potree folder, which contains all resources necessary for rendering the scene. The actual HTML page where the model is located is stored in the directory potree-1.3/model_out/examples/ , and can be accessed by this once uploaded.

FZ.jpg

The final version of the model generated is viewable at the directory here –

EDIT: I’ve lost the original model for this, though will reupload a new version soon

If the Potree stuff is a bit too hairy CloudCompare is a brilliant software for toying with models, I recommend giving it some time as it’s an extremely useful software package!

  • Conclusion

This is a basic tutorial on how to rapidly get 3D models online using nothing but a handheld camera and a laptop. Including taking the images this process took around 20 minutes, but can be speeded up in many ways (including taking better but fewer images). The cloudcompare step can be skipped to speed up even further, but having a ‘ground floor’ plane is in my opinion almost a necessity for producing a model.

This is not intended to be best practice photogrammetry or even close, this is intended to give an overview on modern photogrammetric processes and how they can be applied to rapidly generate approximations to real world objects. These can be then cleaned and models generated for use in applications such as 3D printing, videogames or interactive gallerys.

  • Complete software list

Photoscan

CloudCompare

Potree

Filezilla

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