One of HoloLens’ lowest hanging fruit for AEC–laying a BIM model over the real world for reference, QA, and comparison–remains tantalizingly out of reach. For one, AR devices are mobile computers, so they still have difficulty computing large models. Additionally, they are only pretty good at tracking where they are in space, but not quite accurate enough for quality assurance checks.
Lucky for us, Redcrater is about to release an application for exporting Revit models to HoloLens that could go a long way toward BIM more usable in augmented reality. Meet Revit HoloView.
How to Process BIM for AR
According to software architect Peter Neil, Redcrater ran into problems with large file sizes early on in HoloView’s development.
“One of our beta customers wanted to use it for factories,” he says. “When they were looking at low density areas like warehousing, the FPS [frames per second]performance was good. When they were looking at complex pipes and machinery, the performance was slow.”
Where most applications deal with large files by reducing polygon count, Redcrater devised a strategy that retains the full detail of the original Revit model. When processing gets slow, users can pull up a settings pane and tweak the viewing distance. This enables users to decide how much information they need to display at any given time, and hide everything else.
“For high density objects,” Neil says, “customers set the distance short, but for lower density areas they can set the viewing to long distance.”
The HoloView web service also plays a crucial part in making BIM models friendlier for HoloLens. When users export a file from Revit and upload it to the web service, it compresses the file to 1/3 of its original size and runs a routine that produces a fully pre-cooked file. That means no additional processing steps in the field and a more responsive experience.
An added benefit: That pre-processing enables HoloView users to access their BIM models in wifi-denied areas, like, say, a construction site.
More Accurate Positioning
Which brings us to the second problem.
“One of things we found very early on in development,” Neil said, “is that the HoloLens’ spatial mapping is not accurate enough to align a BIM model to a real space — often the spatial mapping isn’t flush to walls, and for some parts of buildings it will only map fragments rather than the complete structure.”
HoloView addresses this problem in two ways. First, the program displays a spatial mesh of the environment before it performs the initial alignment, giving users visual feedback so they can determine when the HoloLens has worked out its environment enough to set the model in position. Once that rough alignment is complete, the software allows for fine adjustment with rotation and movement tools. Neil says that this workflow enables alignment of the BIM down to 1 cm accuracy.
The result is a BIM model that’s easily viewable on your AR device, and accurate enough for use in a number of applications. Neil says the software is currently in beta testing, but Redcrater is planning on bringing it to market in the very short term.