Surface drawing gives you the ability to create 3D data by marking in only one photograph. This is done by drawing “on” a surface that is 3D. Surface Drawing is useful for drawing/modeling detailed patterns that lie on one plane (such as brick or stonework on the facade of a building). Surface Drawing requires no referencing so detailed patterns and curves are much easier to mark.
Surface Drawing is also useful for drawing curves or lines that lie on planes from a single photograph (such as a skid mark on a road surface).
Surface Drawing requires Surfaces. These Surfaces must project onto an oriented photograph.
You can mark Surface Drawings at any time, and they will update automatically when anything changes (such as the orientation of the photo/camera station or the shape of the underlying Surfaces).
Note, compare this to Outlines (a form of surface drawing with more CAD-like features).
To use Surface Draw:
• Make sure you have one or more Surfaces displayed in 3D in the photograph (they do not need to be visible to be used but you might find it easier if 3D Surfaces are turned on so the surfaces being drawn on can be seen).
•
Pick up the Surface Draw tool 
.
•
Decide if you will be drawing straight lines or
curves. If curves pick the curve option from the toolbar 
.
• Click the first point inside a Surface.
• Proceed to draw your pattern by drawing Surface Draw points. If the surface extends onto another photo, you can continue to mark the surface draw on other photos (this only applies to Surface Draw Lines, Surface Draw Curves cannot be drawn across multiple photos). Note that when a photo's 3D Surface Draw visibility is turned on, and a new Surface Draw is started on top of the projection of an existing Surface Draw Point, a prompt will ask if you want to start the Surface Draw using that existing point or create a new one.
• Whenever you click the right mouse button the menu will appear where you can pick "End Draw" and the line drawing will stop.
• Once the first point has been drawn inside a Surface, subsequent points in a Surface Draw line can be drawn outside of any Surfaces. These points are called "Extended Surface Draw" points.
• If using the Surface curve tool, there is an option to “Create Corner Point” which directs the curve in a new direction without starting a new one. You can also convert an existing curve point to a corner point - this will split the curve into two at that point creating a sharp corner. This is useful for tracing templates or shapes and using it is more efficient than starting a new curve.
Surface Draw points are always assigned to one and only one Surface. However, on a Surface Draw point’s Properties, you can set the Surface ID to which it is assigned (the Surface Draw point be positioned at the projected location on the assigned surface plane). It is from this assigned Surface that Surface Drawing computes its 3D planar position. Lines or curves attached to the Surface Draw points will connect to the point regardless of the surface it is assigned to. When you select a Surface Draw point, its associated surface will highlight in the 3D Viewer (or projected surface on a photo).
On a Surface Draw point’s properties, the Surface ID property shows the point’s associated Surface. When you select the property, The Select Surface verb appears (along with a “…” button) where you can select a new Surface to associate with the point – a menu of surfaces appears and as you mouse over the ID in the menu, the associated surface highlights on photos and the 3D Viewer.
When the first Surface Draw point click is NOT over a surface, a warning/prompt will appear showing how far that point is from the nearest surface to be used for that Surface Draw.
Note that you cannot set a Surface Draw point's property to "do not use in processing" because a surface draw point's 3D position is based on the surface on which it lies. Individual surface draw points are not used in processing.
When deleting a surface draw curve, its points will automatically be deleted. This differs from a surface draw line because the curve is a single entity, while surface draw lines are individual segments. A setting on the Preferences dialog (Curves and Surfaces panel) can be set to retain the points after curve deletion.