5.1. Tutorial: Using projected stripes

This section gives more details on capturing images with a projected stripe pattern for creating more accurate models.

You can project a horizontal stripe pattern and take photos from a high-up and lower down viewpoint (the recommended approach). The object will need to be placed on the radial calibration mat (or using the domino targets which should be visible in all the photos.

Starting Point

To speedup image capture we recommend you use two digital cameras or a computer controlled turntable or both.

If you place your camera positions above and below the projector use the "horizontal" stripe pattern. Your setup should look like this...

Figure 5.1.1. Setup with vertically arranged cameras using the horizontal stripe pattern.

If you place your cameras either size of the projector (horizontally), use the vertical stripe pattern and your setup should look like this...

Figure 5.1.2. Setup with horizontally arranged cameras using the vertical stripe pattern.

The pattern images can be found in the "slides" folder in the 3DSOM Pro application folder which by default will be C:/Program Files/3DSOM Pro/slides/ or C:/Program Files (x86)/3DSOM Pro/slides/

If you have a computer controlled turntable you can use a single camera. First move the camera to the first camera position ("camera1") and take a sequence of photos using the turntable software. Reset the turntable to "home" position. Then move the camera to the second position ("camera2") and take another sequence from the precisely same angles using the turntable software.

Select the slide based on the type of pattern ("horizontal stripes", "vertical stripes") and the digitial projector resolution (SVGA 800x600, XGA 1024x768, WXGA 1280x800 or HD 1920x1080). There are also "fine" quality versions of the pattern with thinner stripes. Only use these if you are able to focus the pattern to appear clear, sharp and in focus on the object. If the fine pattern is out of focus or too blurred and the lines are not distinct then use the normal pattern which has wider separation between the stripes.

Make sure the projected stripes cover the whole object and appear reasonably sharp and in focus

An easy way to display the pattern on your projector is to set the stripe pattern image as the desktop background and to extend your desktop so that the projector acts as a "secondary" monitor. Alternatively use the imaging control software provided with your hardware.

Step 1

Take your photographs making sure that you have rotated the object to around 16 positions and have two (or more) images for each position. You will need to ensure that dots on the calibration target(s) are detectable in the photos - you may need to use a spot light to illuminate the mat. The projected pattern should be clearly visible and focused on the object — you may need to darken the room depending on your projector's power.

If you are using multiple cameras try to fire them off at approximately the same time - so they have similar timestamps. Alternatively you should rename the shots so that the files taken at the same rotation have the same numerical suffix (not including the file extension). e.g. camera1_0001.jpg and camera2_0001.jpg. See File Naming Convention.

TIP:

If your camera positions are vertically spaced (i.e. the elevation angle changes but the object rotation is fixed) then this will be automatically detected so you won't need to rename the images. Make sure these shots are set to be the "stripes" image type and use the "...using trailing digits" (default) option.

Figure 5.1.3. Image from upper camera
Figure 5.1.4. Image from lower camera

Take additional shots from the same angles with the projector turned off and normal (diffuse) lighting. These shots will be used for masking and texturing in the normal way.

Step 2

Start a new project and load in all your photos. If your files have not been named using the 3DSOM Pro naming convention you will need to manually identify the stripe shots. Select the thumbnails corresponding to the stripe shots and use Image Type > Stripes (Cloud Only) menu item from the Main Menu > Images menu to identify these as stripe shots.

Step 3

Mask all or some of the images that are easy to mask (taken without the projected pattern).

You can now use the ID_MAKE_ALL.jpgMake all button to build a fully textured 3D model. Alternatively follow the remaining steps below to manually step through the process.

Step 4

Build your initial wireframe model in the normal way using the ID_MAKE_SURFACE.jpgGenerate surface... button.

Figure 5.1.5. Initial model
Step 5

Now build a point cloud by selecting the ID_CALC_POINTCLOUD.jpgGenerate Point Cloud button. Use the "...using trailing digits" default option if the images have been named with the same numerical suffix or were taken with vertically spaced cameras. Otherwise you can select either the "...using timestamp" option if the images taken from both cameras were taken simultaneously (or within a 0.5 seconds).

Figure 5.1.6. Point cloud
Step 6

optimise your surface using the masks and point cloud using the ID_MAKE_SURFACE.jpgGenerate surface... button.

Figure 5.1.7. Optimized model
Step 7

Build the texture maps in the normal way using the ID_MAKE_TEXTURE.jpgGenerate texture maps... button.