vGIS AR uses computer-generated 3D visuals superimposed on top of live video to augment a user’s view with helpful information.
When thinking about 3D visuals and evaluating 3D objects, it is important to consider perspective. From the observer’s point of view, large objects that are located far away appear identical in size to smaller objects located close by. To the observer in Fig. 1, the green, the red and the blue pipes will appear of the same size and in the same location.
In the physical world, the human brain is capable of processing myriad visual clues, such as the relative positioning of objects and perspective shifts, attaining an instant understanding of object size and location. In augmented reality, these clues are not available, as virtual objects are always drawn on top of other objects, which may lead to confusion about object placement.
For instance, Figure 1 shows the green and the red pipes on the background, while the bush is on the foreground. However, since both pipes are displayed on the device that is closer to the observer than the bush, they will be drawn “on top” of the bush. See another example below (Fig. 2).
Figure 2 shows infrastructure objects drawn in their correct locations. However, due to the nature of augmented reality, these objects appear in the foreground rather than behind objects such as the mailboxes and the tree. This phenomenon makes it crucial to consider 3D perspective when evaluating object size and position.
Note: To help you understand object placement, vGIS shows the positions of objects at depth and also shows their projections (dashed lines) on the road surface (Fig. 3). As you move around, this combination of the object plus its projection gives visual clues as to the object’s location and size.
How do you know that you are standing right on top of a pipe? Once the dashed line aligns with the pipe it represents, you are positioned directly above the pipe.
When working with data set containing assets with absolute elevation, vGIS AR can track its position relative to virtual objects with high-accuracy. For other data set types, vGIS uses topographic maps provided by Bing, Esri and Google to calculate object elevation. Factoring in elevation is crucial for areas with noticeable landscape irregularities.
Note: vGIS’s reliance on external sources, such as Google Maps, may introduce errors. If an area’s elevation map (or digital terrain model - DTM) is imperfect, which happens occasionally, objects in vGIS may appear misaligned. In most cases, misalignment is an optical illusion; walking towards a point of interest reveals that the object is placed exactly where it should be.
Note: DTMs rarely capture small, local elevation changes, such as road grades or sloping front yards. This may cause vGIS displays to appear misaligned.
How Do I Know Where Everything Is?
Combining landscape maps with a 3D perspective may occasionally produce visuals that appear misaligned. For instance, Fig. 4a shows two catch basins that look as if they are positioned on the sidewalk.
Yet, standing over the catch basins reveals that they are exactly where they should be— on the street, slightly away from the sidewalk (Fig. 4b).