5.3. Tutorial: Merging multiple scans


In some cases more than one or two images from underneath the object are needed or are desirable to fully capture the shape or texture of the object.

The natural way to handle such an object is to take two sets of photographs, turning the object over in between. In normal operation, 3DSOM Pro assumes that the object does not move relative to the mat, but this is not the case, so the second set of images has to be aligned with the first set.


The Align Wizard is used to help the process of merging the two sets of images together to form a single project. 3DSOM Pro needs to determine how the object has moved between taking the two sets of photographs.

This can be automated by building a partial model from one set of photos and letting the software compute how the second set is oriented relative to the first set. Any number of additional scans can be merged in this manner.

Starting Point

Make sure your images for the two scans are stored in separate folders as this will help keep track of which images were taken for each scan (and avoid file naming conflicts). It can help to store the second scan in a subfolder e.g. named "side_shots").

For the example shots in this tutorial, we have captured separate calibration images, normal images and stripe images of a fossil (vertebra) using two cameras, with the object sitting flat. We then rotated the object onto it's side and took another complete sequence of the normal and stripe images - the cameras and turntable remained fixed so we didn't need to taken a second set of calibration shots.

5.3.1. Fully automated workflow

3DSOM Pro now contains a fully automated workflow for stitching two scans once the images are masked.

Step 1 - Load all the photos

Create a new project and load the in the images from the first folder. In our example we have calibration, normal and stripe images for two cameras with our fossil object sitting flat (thumbnails below).

Add the images from the 2nd scan (which should be in a separate folder) using the Images > Add Images... menu item from the Main Menu > Images menu. In our example the second scan was taken by rotating the object on it's side and capturing another sequence of normal and stripes shots from both cameras.

Step 2 - Mask shots

If there are no masks, create masks for all the normal shots from both scans using the ID_MAKE_MASKS.jpgMask all images... button.

Step 3 - Hit "GO"

Hit the ID_MAKE_ALL.jpgMake all button and select the desired quality and optionally texture settings.

Hit OK and 3DSOM Pro will automatically merge the two scans and build a complete 3D model using all your photos.

Figure 5.3.2. Textured complete mesh

5.3.2. Manually supervised workflow

Step 1 - Build a wireframe from the first scan

Create a new project and load in the images for the first scan. In our example we have calibration, normal and stripe images for two cameras with our fossil object sitting flat.

If there are no masks, create masks for the normal shots using the ID_MAKE_MASKS.jpgMask all images... button.

Generate a quick wireframe mesh using the ID_MAKE_SURFACE.jpgGenerate surface... button. There is no need to optimise the mesh or create a point cloud at this stage.


If the object has few geometrical features it may also be worth generating a rough surface texture at this stage to help with the alignment.

Step 2

If your second scan also contains calibration shots then you should delete all the existing calibration shots from the current project by selecting the thumbnails and using the Images > Delete Images menu item from the Main Menu > Images menu.

Add the images from the 2nd scan using the Images > Add Images... menu item from the Main Menu > Images menu. In our example the second scan was taken by rotating the object on it's side and capturing another sequence of normal and stripes shots from both cameras.

If there were no masks, click the ID_MAKE_MASKS.jpgMask all images... button to mask the newly added shots (they should already be selected).

Step 3

Select the second set of images (it doesn't matter if they are currently marked as rejected) and choose the Images > Align Images... menu item. Make sure all the images in the second scan were selected including the normal and stripe shots for all cameras used. The Align Wizard will be shown. All the other images now appear locked (greyed out) in the Thumbnail Window.

Select the "Merge Group" option from the wizard welcome page — all the selected images are taken with the object in a fixed position against the mat and can therefore be aligned in a single step.

Choose Next > button to move onto the next page.

Step 4

At this point, look at View Model Window — it displays the current model semi-transparently over one of the selected set of images. You can rotate and move the model as normal. Use the ID_MODEL_NEXTVIEW.jpgNext view button (and the ID_MODEL_LASTVIEW.jpgLast view button) on the View Model toolbar if you want to move back to where you were previously.

You can use either the "playback" buttons (IDC_ALIGN_FIRST.jpgFirst image button, IDC_ALIGN_PREV.jpgPrevious image button, IDC_ALIGN_NEXT.jpgNext image button and IDC_ALIGN_LAST.jpgLast image button) in the wizard to move to a different image. When you change to a different image, the model will be rotated so that it remains in a consistent orientation relative to the second set of images.


You can also double-click on an image in the Thumbnail Window or drag an image from the Thumbnail Window onto the View Model Window to switch to this image.

Figure 5.3.4. The same orientation of the model seen from two different cameras against their respective backdrop images.
Step 5

As long as there are enough images in the second set and they have been properly masked, 3DSOM Pro will be able to align the object automatically. This is a great advantage, since it is tedious to get the alignment right by hand - it can look good from one image, but from a different image can be far out of alignment. Use the Guess button to get 3DSOM Pro to pick an initial alignment.


Switch between View wireframe model (F5), and View flat shaded model (F6) or View textured model (F7) display modes to help show the model up against the photograph.

Sometimes, particularly with fairly symmetric objects, 3DSOM Pro will be unable to tell which way round the object is — each time you click the Guess button it will cycle through a series of possible alignments.

Don't worry if the match isn't perfect at this stage - choose "Next" to proceed to the optimisation stage once you are happy the orientation is roughly correct relative to a couple of images.


If none of the guesses came close, manually rotate and move the object until it is roughly aligned.

Step 6

Hit the Start button to begin optimising the alignment. During the optimisation stage, 3DSOM Pro attempts to make minor changes to the orientation and position of the object whilst checking that it matches the silhouettes of the chosen images. You will see the object "vibrate" during this process and you can check the alignment against different images as before.

You can stop when you are happy with the results. Use ID_MODEL_LASTVIEW.jpgLast view button from the View Model toolbar to revert to the previous alignment.


Check the alignment using images from cameras that were widely apart from e ach other since this is more likely to show any problems quickly.

Step 7

Closing the wizard will fix the alignment of the second set of images relative to the first. They can now be used in the project in the same way that the original set of images were.

In our example, we now have a complete set of masked normal shots and stripe shots from all round the object. To build the model we simply hit the ID_MAKE_ALL.jpgMake all button.