Reference: The Edit Markers Window

3.6. Reference: The Edit Markers Window

This section describes the tools available for placing marker points as well as marking curves, polygon edges and faces in multiple images.

For projects without the calibration mat, manually placed marker points are an alternative approach to obtain estimates of the camera position and orientation parameters (required to generate a 3D model). Each marker has a unique identifier (or ID). Each marker should be placed at the image location of a specific feature in two or more photographs.

Once camera estimates are known (using markers or a calibration mat) the Edit Markers Window also provides tools for defining points, curves and straight edges visible in several photos. By matching these features across multiple images a set of sampled 3D points are obtained. The points are included in the point cloud which is used when optimising the 3D model to create a more accurate result (see Optimising the surface geometry).

Alternatively, a user-specified closed curve can be extruded to create a 3D region that can be removed from the existing 3D model (Boolean subtraction).

Figure 3.6.1. The Edit Markers toolbar and Edit Markers Window.

All the tools available from the Edit Markers toolbar can also be accessed from the Main Menu > Marker Tools menu. This menu can be accessed either from the main menubar when the Edit Markers Window is active or by right-clicking in the Edit Markers Window.

3.6.1. Viewing images

The Edit Markers Window consists of 1 to 4 subwindows (by default the window is split vertically into a left and right subwindow). Each subwindow can show a separate photograph allowing you to compare the photos whilst placing the markers. To view an image in a subwindow simply drag a thumbnail from the Thumbnail Window into the subwindow.

You can quickly flick through the images shown in a subwindow using the controls at the bottom of each subwindow. Click |< to switch to the first thumbnail, >| to switch to the last thumbnail, < to switch to the previous thumbnail and > to switch to the next thumbnail. Hold down the < or > buttons to scroll through the images quickly.

With the Zoom mode button selected, dragging the mouse up and down in a subwindow zooms into or out of the selected image allowing more or less detail to be seen. You can also access zoom mode when the Select or place button is selected by holding the CTRL key as you left-drag with the mouse.

With the Pan mode button selected, dragging the mouse in a subwindow scrolls around the image allowing a different zoomed-in area to be shown. To scroll an image whilst the Select or place button is selected hold down the SHIFT key whilst dragging with the mouse.

The currently active subwindow is displayed outlined in red. Hold the SPACE bar to temporarily zoom into the active window until the SPACE bar is released.

3.6.2. Marking features

To mark features (points, curves, lines or faces) the Select or place button needs to be selected.

Select the Pin Marker Mode button to create or edit the point marker features. These are displayed using a "drawing pin" icon overlaid on the photographs. Each point marker represents a specific location on the 3D model such as the centre of an eye or the corner of an adhesive label etc. The point marker can then be manually located in a number of photos (normally 2 or more).

TIP:	Make sure your point features are truly fixed points on the 3D model and do not change location. For example silhouette cusps are generally 2D features that do not represent a static location on the 3D object.

Select the Curve mode button to create or edit curves. These can be outlines or edges on the texture of the object such as the boundary of an adhesive label, seam on an item of clothing or crease or sharp edge on the 3D object. A curve marker should be a specific 3D edge feature although the whole edge need not be visible in each photo where it is marked.

Select the Polygon mode button to create straight edges joining the marker points and if applicable polygonal faces. You can use this mode to simply create a 3D straight edge or crease joining two existing marker points or you can define a complete polygonal model with marker points at all the vertices (useful if your object is basically a polygon e.g. a cube, simple office building etc).

Select the edit mode button to switch to curve editing mode where you can fine tune the node positions and tangents for existing marked curves.

3.6.3. Selecting or deleting marked features

A numerical identifier (ID) is automatically created for each new marker point or curve. The identifiers are specific to the type of feature so there may be a point marker with ID 0 and a separate curve marker with the same ID.

The currently selected point or curve is highlighted in red. You can enter the identifier (number) in the "Selected" text box to change the current selection or use the adjacent arrow buttons to "jog" the selection to the next or previous identifier.

Click the Deselect button to deselect the currently selected marker. This is useful where you need to start marking out a completely new feature in a photo which does not correspond to the currently selected feature. When you create a marker with none selected a new identifier will automatically be assigned. This button can be used when marking points, curves, edges or faces.

Click the Delete selected button to delete the currently selected feature marker from the photo in the active subwindow (the active subwindow is outlined in red). You can use this button to delete a feature you have incorrectly marked in a photo e.g. when that feature is not visible in the photo. To completely remove a feature you will need to delete it in every image where it's location has been marked. This button can be used when marking points, curves, edges or faces.

3.6.4. Changing the window layout

Select the Single View button to remove the split screen layout and use a single subwindow.

Select the Split horizontally button to split the window horizontally to display two subwindows one above the other.

Select the Split vertically button to split the window vertically to display two subwindows side by side.

Select the Split horizontally and vertically button to split the window both vertically and horizontally to display four subwindows in a 2 by 2 grid.

3.6.5. Defining point markers

To switch to marking points select the Pin Marker Mode button.

If no marker point is selected then clicking on a photo in a subwindow will place a new marker feature and assign a new identifier for it.

The selected marker point is displayed with a red pin. Other markers are displayed in blue. At any point, you can click on a blue pin to change the current selection.

If a marker is already selected then clicking on a photo which does not already have this marker located will define the image location of the selected marker. (In this case a "=" cursor is displayed.) In this way you can define the locations of a 3D object feature in multiple images.

If a marker is already selected and already located in a subwindow photo then clicking will create a new marker. In this case a "+" cursor is displayed to show that you will be creating a new marker feature. This mechanism avoids the need to deselect the current selection every time you wish to create a new marker feature.

As you move the cursor over a subwindow, nearby point markers are displayed opaquely with further away markers displayed transparently. This will also be reflected in markers in the other subwindows.

Click and drag on a marker pin to adjust the location. Hold the SPACE bar to zoom in whilst doing this for fine control.

If you realise that the same feature point has erroneously been given two different idetifiers in two photos, you can merge them together to indicate they are the same feature. To do this select the first marker pin, then click the Merge markers button, then click the second marker pin. Alterantively if no marker is selected you can click the button, then click the first marker pin and then click the second marker pin.

If the Toggle auto-update button is selected (the default setting) then 3DSOM Pro will automatically try to estimate the camera parameters as you add point markers — assuming you haven't used the calibration mat. This can start to get quite slow if you have marked many features so you can turn off this feature by clicking the button. To update camera estimates manually use the Processing > Solve Cameras menu item.

See the Creating a 3D model from photographs without using a calibration mat tutorial for details of the workflow.

3.6.6. Defining curve features

To switch to marking curves select the Curve mode button.

As for point markers, clicking in the current image will create a new curve feature if there is none currently selected. Click and drag to add another curve boundary point. The locations clicked will be interpolated by a smooth curve - curve tangents will automatically be defined. If a smooth curve can not be created a sharp corner will be created instead.

Hold the CTRL whilst clicking to create a sharp corner. Click the starting point to close the curve.

Use Undo CTRL Z and Redo CTRL Y to undo or redo the last curve node placement.

The currently selected curve will be displayed in red. The active curve endpoint is highlighted. Clicking on any curve node toggles selection of that curve.

To extend a curve from the starting point (backwards) the curve can be deselected, then the starting point selected once (selects the curve) and once more (makes the startpoint the active end).

A curve edge feature on the 3D object (e.g. a seam in a dress) can consist of any number of closed or non-closed segments in any particular photo. e.g. the seam may be hidden behind another part of the object and hence require two separate segments.

If a closed curve is being defined to create an extruded "cutter" shape then in general this should have a unique identifier which should not be used in any of the other images.

If the Snap curves button is selected (the default setting) then curve tangents will be automatically optimised so that the curve follows edge features in the current photo.

If the Sharp crease button is selected (the default setting) then the curve will be marked as "crease" or sharp edge for geometry optimisation. If you are marking part of the surface pattern on a smooth object (e.g. outline of a company logo on a flat or smooth part of the object) then toggle this setting by clicking the button.

You can define a closed curve for a photo (with camera parameters solved) and back-project ("extrude") this to create a 3D region by clicking the Extrude selected shape button. You can then adjust the extents of the back-projected region and remove this shape from the current surface. The information will also provide additional constraints if the surface is optimised.

TIP:	If you are defining a curve to back-project or "extrude" then make sure it has a unique identifier so that it is not erroneously matched across multiple images.

If you have defined a curve feature in multiple images where the cameras are known (using the calibration mat or marker points) then sampled edge points will be automatically generated which can be viewed immediately in the View Model Window.

3.6.7. Editing a curve

When in curve marking mode you can toggle the edit mode button to start or finish adjusting the nodes of the currently selected curve.

Click and drag the curve nodes (large squares) to adjust the boundary position.

Click and drag the curve tangent nodes (small squares) to adjust the tangents at boundary nodes. The tangents are adjusted indepedently.

To delete a curve node, click to select it and then use DELETE key.

Use UNDO CTRL Z or REDO CTRL Y to undo or redo your curve node edits.

3.6.8. Defining straight edges and polygonal faces

Before defining edges or faces you will need to place marker points in multiple images. Place these at the image location of the vertices of the edge segment or polygonal face.

Then select the Polygon mode button to join the marker (vertex) points together to create edges and polygons.

If your object is completely polygonal you can construct the 3D object by creating a number of polygonal faces making sure you have markers positioned at every vertex position. See Modeling a polygonal object from markers for a tutorial example.

Alternatively you can simply construct a few straight edge segments for sampling as points in the point cloud used when optimising the surface.

The marker pins will be displayed. Select the start of your edge if not currently selected. You may have to deselect the currently selected pin if this is not on the edge you wish to define.

Select another marker pin and an edge will be created between the newly selected pin and the previously selected pin.

As you create edges they will remain selected (shown red). The current pin ID is displayed (edges do not have IDs). Click the centre of an edge to toggle selection.

To construct a polygonal face, continue to create edges between pins until you have a closed polygon and make sure they are selected. (If the polygon has a hole — create the edges of the hole and select all the edges on the polygon and hole.)

To create a "front facing" polygon, select the polygon edges and click the Create front face button. Front facing polygons have a normal that points out of the screen. E.g. for a cube placed on the ground you can see 3 front-facing square faces in a typical image.

Occasionally you may need to create a "back facing" polygon by clicking the Create back face button - if the face can be seen facing outwards in any of the images. E.g. the bottom face of a cube placed on the ground can not be seen - so you need to select the bottom edges in side views and click this button.

Try to create a "closed" polygon. i.e. there are no missing faces - as some of the 3DSOM Pro functions will not work as expected if the current geometry is not closed.

Once you have created some faces you can use Next face button and Previous face button to select the next or previous face.

Use the DELETE to remove the currently selected face. Once you have deleted the face, the face edges will remain (unselected).

To delete one or mores edges select them (displayed in red) and hit the DELETE key.

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