Does a home scanning app use GPS and compass indoors?
Yes, a LiDAR scan can read the phone's compass and GPS along the way, and use them to set a north arrow on the drawing and find the home's approximate location. Both are weaker indoors than outdoors, and it is worth knowing why.
Short answer: Yes. During a LiDAR scan, an app can read the phone's digital compass and the camera's direction in augmented reality (AR), and combine them to work out the home's north direction. At the same time it can read the GPS position to find the address. The compass is less accurate indoors, because metal in walls and floors disturbs the magnetic field — so the north arrow is a starting point you should check, not a guaranteed answer.
How does an app find north while you scan indoors?
Two signals are combined. The phone's digital compass measures the earth's magnetic field and gives a heading in degrees. At the same time, the AR system (the augmented reality that the LiDAR scan runs in) tracks the camera's direction in the room, frame by frame, as you move the phone around. By linking the compass heading at the moment the scan starts to the camera's direction in the AR space, the app can work out how the home's walls are oriented relative to north — without you having to point the phone north yourself and press a button.
Why is a compass weaker indoors than outdoors?
Because it measures a magnetic field, and buildings are full of things that distort magnetic fields: reinforcing steel in concrete, steel beams, radiators, refrigerators, speakers with magnets, and the wiring inside the walls. The closer to a large amount of metal, the bigger the deviation — a couple of degrees in some places, twenty or more in others. It is the same phenomenon that makes an ordinary compass needle swing near a stove.
A single compass reading at the start of the scan is therefore not perfect. Most apps try to compensate by using the shorter, more reliable AR tracking for the actual rotation inside the house, and only the compass to "calibrate" the overall direction once.
Does GPS even work indoors?
Partly. The GPS signal comes from satellites and is markedly weakened by the roof and walls, but it rarely disappears entirely — especially not near windows or in homes with lightweight roof structures. The position becomes less accurate than outdoors, where an accuracy of a few metres is normal, but it is usually good enough to look up the right address, which is what it is used for: a starting point for an address lookup that you can correct by hand if it gets it wrong.
What is the home's north direction and position actually used for?
- The north arrow on the floor plan. It shows how the home is oriented, without you having to measure it with a compass after the scan.
- A daylight study. For an app to show where the sun sits relative to the home on a given date and time, it needs to know both the home's north direction and its geographic position — the sun's path depends on latitude.
- Address lookup. The GPS position can be used to suggest an address, so you don't have to type it in by hand.
What if the compass gets it wrong?
Then the north arrow points the wrong way, and a daylight study built on top of it will show the sun on the wrong side of the house. It is not an error that corrects itself — it is one you only notice by comparing it with something you already know: the sunrise seen from a particular window, an address whose facade direction you know, or a map. Most good apps therefore let you correct the north direction by hand after the scan, precisely because the automatic reading is a guess, not a measurement taken with a physical compass in hand.
Can you scan without granting the app location permission?
Yes, usually, but then you lose the features built on position — address lookup and an accurate daylight study. Scanning the geometry of the rooms itself does not require GPS or compass; they are only used for the layer of information that sits on top of the geometry: where the home is, and which way it faces.
Is it a privacy concern that the app knows the home's position?
It is a piece of information you can judge the value of sharing yourself. A home's address is often already publicly available elsewhere — in a listing, in the public building register, on a map — but it is still reasonable to ask where the information is stored, and whether it leaves the phone. That is a question you should be able to get a clear answer to from any app that asks for location permission.
Can you correct the north arrow afterwards, if it is wrong?
In an app that stores the north direction as an ordinary number attached to the home — not something locked into the scan itself — it is typically possible to rotate the north arrow by hand afterwards, if you discover it is pointing the wrong way. That is the only robust fix for a signal that is inherently imprecise indoors.
What HouseSense does
HouseSense reads the phone's compass heading and the camera's direction in AR at the start of the scan and derives the home's north direction from that, along with a GPS position for the address lookup. It requires LiDAR and that you grant the app location permission. The north direction and position are the basis for the north arrow on the floor plan and for the daylight study that shows where the sun sits at the home's facades on a given date — both can be corrected by hand if the automatic reading is off, which is especially likely in homes with a lot of steel and concrete.
How to judge an automatic north reading
- Compare it with something you know. Sunrise seen from a particular window, or a facade whose direction you already know.
- Be more sceptical in homes with a lot of metal — steel beams, underfloor heating with metal pipes, large appliances close to where the scan started.
- Treat it as a first guess, not something that should stand unchallenged in an official drawing or application.
- Correct it by hand, if the app allows it and you can see it is wrong — that is quicker than scanning again.