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Why does the 3D model of the house run slowly on my phone?

A 3D model of a whole home can contain tens of thousands of triangles, shadows recalculated every frame, and light hitting every surface in real time. That is heavy work for a phone, and there are concrete things that make it heavier or lighter.

What makes a 3D model heavy to display?

• Number of triangles (polygons). Everything in a 3D model is built from surfaces, and each surface is usually split into triangles. The more, and the more detailed, the furniture and building parts are, the more triangles the phone's graphics chip has to work through, every single time the frame is drawn — typically 60 times a second.
• Real-time shadows. Working out where the sun casts a shadow and how it moves as you turn the camera is markedly heavier than drawing a surface with a flat colour. Shadows require the whole scene to be "drawn" a second time from the sun's point of view, to work out what lies in shade.
• Light and materials. Surfaces that reflect light realistically — sheen on a floor, transparency in a window — cost more than a flat colour.
• Number of objects, not just size. A room with twenty pieces of furniture is heavier than an empty room of the same size, because each piece of furniture is its own geometry the phone has to keep track of.

Can you see the house without a ceiling?

Most 3D viewers for homes offer a kind of "dollhouse view", where the ceilings are hidden so you can look down into the rooms from above, as if the roof had been lifted off. That is both a practical feature — you get a quick overview of the whole floor plan — and one that eases the load on the phone slightly, because the ceiling surfaces don't need to be drawn and lit while you're looking down.

What do shadows actually cost the battery?

Real-time shadows are among the most expensive effects in 3D graphics, because they need a whole extra "camera" from the sun's position for every frame. On a phone this shows up as warmth in the house and faster battery drain, especially with extended use. That is why it is common for 3D apps to let you switch shadows off when you just want to see the floor plan, and switch them on when you want to assess light conditions or show the house off.

Why is per-layer control better than a single quality setting?

Many programs solve the heavy-load problem with one combined quality dial: high, medium, low. The problem is that a dial like that switches everything on or off at once, even though it's rarely everything that is heavy. A program that instead lets you switch furniture, ceilings, shadows and room lighting off one at a time lets you find exactly the combination that runs smoothly on your phone, without giving up more than you need to.

What can you do yourself if a 3D model is stuttering?

1. Switch off shadows first. They typically cost the most and matter the least for understanding the floor plan.
2. Hide furniture if you're only looking at the building. Furniture adds geometry without changing the house itself.
3. View one floor at a time instead of the whole house at once, if the home has several storeys.
4. Close other apps on the phone. 3D rendering shares the graphics chip with the rest of the system, and a phone with little free memory is pushed harder.
5. Restart the app if it has been running for a while. Extended use can build up memory that isn't released until the app is closed fully.

What can't be helped?

Older phones simply have weaker graphics chips, and there is a limit to how much per-layer control can compensate for that. A home with many rooms and lots of furniture will always be heavier than a single room, whatever settings you adjust. And a program that builds the 3D model from a real floor plan with real measurements is inherently lighter than a photo-realistic scan with millions of coloured points — but never entirely free.

Is a drawn 3D model always lighter than a scanned point cloud?

As a rule of thumb, yes. A 3D model built from a floor plan with real measurements consists of relatively few, clean surfaces — walls are flat rectangles, floors are polygons, and a door is a hole cut out of a wall. A raw scan, by contrast, stores the surface as the camera saw it, with countless small irregularities, colour variations and noise that all have to be drawn individually. That is one reason apps that build their 3D model from measured building parts, rather than directly from the scan's raw data, generally run more smoothly on the same phone — the price is that the model looks more simplified and clean, not photo-realistic.

Does a 3D model get heavier the more floors the house has?

Yes, but less than you'd expect if the app only draws the floor you're looking at. A well-built program typically shows only the active floor in full detail and hides the rest while you're inside the walkthrough view — it is only when the whole house is shown together from outside that every floor loads the graphics chip at once. That is why per-layer control that lets you switch floors off one at a time helps most on large, multi-storey homes: you can isolate exactly the floor you're working with, instead of the phone having to keep track of the whole house at the same time.

Why does it feel like heat and not just a lower frame rate?

A phone's graphics chip and main processor work harder the more they have to compute per second, and that work turns into heat, just as when you play a demanding game for a long time. With brief use you rarely notice it, but keep a heavy 3D model open for several minutes — for instance while showing the house to someone — and the phone can get noticeably warm, and some phones automatically throttle performance to protect themselves from overheating, which feels like the model suddenly starting to stutter, even though you haven't changed anything.

What HouseSense does

HouseSense has its own layer panel, where ceilings, furniture, room lighting and shadows can each be switched off individually, and each floor can be shown on its own. The panel shows what each item costs to have switched on, and it doesn't close itself after every tap, so you can test several combinations in a row without having to reopen the menu each time.