ARC3D User's Guide

Table of Contents

1. Quick Start

ARC3D is a tool for creating 3D models out of a set of images. To create a 3D reconstruction with ARC3D you need to:

1. Download client tool and obtain an user account from the ARC3D website.
2. Take some photos of an object to reconstruct. Take many images with large overlap while moving around the object. See section Taking Photos. for more details.
3. Upload the images with the client tool. See section Client Tool. for more details.
4. Obtain an e-mail with the result, this normally takes 30 min to 3 hours.
5. View the resulting model in a tool such as Meshlab: http://meshlab.sourceforge.net

2. Taking Photos

ARC3D is easy to use and can process casually taking images taken in random order. However, to achieve a high quality result, please consider the following guidlines.

1. Move between the photos. Do not pan (as is done for panorama shooting).
2. Take many photos, more than you might expect. For a facade, we recommend 10-15 images. For a complete 360 degree sequence, we recommend around 50 images. This means that the angle should be less than 10 degrees between the shots.
3. Ensure a large overlap between the images. Ideally 90% of the previous image should be visible in the next. 3D reconstruciton is all about finding the same object in multiple images and a large overlap greatly aids this process.
4. Avoid blurry images due to motion blur or out-of-focus. Set the exposure and focus such that all parts of the object stays sharp and use a tripod if the lighting is dim.
5. Avoid noisy images by reducing the ISO setting of your camera. Use a tripod if necessary.
6. For best result, use the same camera with the same focal length (zoom) and the same resolution throughout the image sequence.
7. Do not process your images before upload. Our algorithms can make use of information stored in the EXIF-tag of JPG images to improve the reconstruction. Processing the images with an image editing program may remove this information.
8. If you are unsure about your camera, use an EXIF reader to find out if your images contains EXIF data. Check that the Focal Length tag is present.
9. Not all surfaces can be reconstructed with ARC3D. In particular, the surfaces have to be textured and non specular. This means that the surface should have irregular intensity changes and not be too reflective. For instance, A completely white plate, glass buildings, shiny cars and chromed machine parts are difficult or impossible to reconstruct. Brick, stone and other textured items are easier.
10. Turn table objects can be reconstructed as long as your camera provides the focal length EXIF tag.
11. If you are inexperienced with ARC3D, try to reconstruct some simple objects before moving on to larger projects.

3. Client Tool

The client tool is used to upload images to the ARC3D server.

3.1 Uploading images

1. Test connection. Make sure that the ARC3D server is online and that you have a connection. See section Testing the connection for details.
2. Load images. Select open images on the file menu. The images will appear in the left column of the tool.
3. Upload images on the file menu will start the uploading process.
4. Subsampling. Subsampling (reducing the size) of your images will make them faster to transfer but will give you a lower resolution model. Change the default value of 100% only if the transfer is too slow.
5. User login. Provide your username and password.
6. Names. Provide a name for your scene (where the object is) and the sequence (which specific object). Optionally, provide your institution.
7. Start transfer. The images are uploaded to our server. You will recieve a notification when the transfer is complete. If the connection is lost, the upload can be resumed. Simply select the same images with the same scene/sequence name as before.

3.2 Testing the connection

The Server status box in the bottom-left corner gives you information about your connection to the ARC3D server. Messages will appear here if the server is down for maintainance or if your computer has problems to connect to ARC3D.

If you are behind a firewall, it might be necessary to setup the proxy settings on the connection menu. Please ask your network administrator for details.

You can also perform a connection test on the connection menu.

4. Using the Results

4.1 Mesh

The 3D model can be directly loaded in a mesh processing tool such as Meshlab.

4.2 Depth maps

The individual depth maps can be loaded in Meshlab by opening the "model.v3d" file. In the ARC3D importer you may directly save the depth maps as PLY or import them to the Meshlab workspace for furter processing.

4.3 Camera files

This is the format of the camera files (for advanced users)

fx 0 cx
0 fy cy
0 0 1

k1 k2 k3

R11 R12 R13
R21 R22 R23
R31 R32 R33

T_x T_y T_z

width height

• fx, fy: Focal length in x and y directions
• cx, cy: Principal point
• k1, k2, k3: Radial distortion parameters
• R: Rotation matrix from camera to model frame
• t: Translation vector of camera in world frame

To project a 3D point M to the image plane. Only formulas for the x-coordinate is shown. (') denotes transpose.

• Compute normalized image coords: x_norm = R'(M - T)[0] / R'(M - T)[2]
• Apply distortion: x_dist = x_norm*(1 + k1*r^2 + k2*r^4 + k3*r^6), r = sqrt(x_norm^2 + y_norm^2)
• Project to image plane: x_img = fx*x_norm + cx
• Similar for the y coordinate

5. Troubleshooting

• If you cannot load the resulting model, try to reduce the size of the texure image (textured_mesh.jpg) using an image editing software.

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