Translate GPS coordinates to location on PDF Map

Question

Hi everyone,

I'd like to know (from a high level view) what would be required to take a pdf floor plan of a building and determine where exactly you are on that floor plan using GPS coordinates? In addition to location, the user would be presented with a "turn by turn" directions to another point on the map, navigating down hallways, between cubicles, etc.

Use case: an iPhone app that determined a user's location and guided them to a conference room or person's office in the building.

I realize that this is by no means trivial, but any help is appreciated. Thanks!

Answer 1

GPS may not be accurate enough for this purpose, especially indoors. Assuming errors on the order of 10 meters, you'll have difficulty determining which floor the user is on.

Here's a neat (?) idea that might work: can you post some "You are here" placards at various locations around the building? You could label each one with a unique, machine-readable location code (maybe a QR code or something similar), then take an image using the camera, have your app read that image and interpret the location code, and use that instead of GPS to determine the start location.

Answer 2

GPS inside? That's your first -- and biggest -- hurdle.

Next hurdle is knowing the GPS coordinates of at least three points on that PDF to define the plane of of your map in the real world. (The PDF will need to be to scale, of course.)

So that gives you where you are on the PDF. Now you'll need to figure out some way to determine where you can walk (or where you can't) to get directions.

Answer 3

It's an interesting problem. When you're using Core Location, you're not necessarily using GPS. Using WiFi and cell tower triangulation, you can get pretty good location results. So from Core Location you get a latitude and longitude fix. (You might also get altitude info, since GPS data is 3-dimensional. You also will get an accuracy value.)

So you have lat and lon. You need to map these coordinates to the PDF plan's coordinates. Assuming that the plan is aligned with the latitude and longitude lines, and that you have a lat-long fix for one of the points on the plan, you need to calculate the x-axis scale and y-axis scale. Then it's some calculations to map the lat-long to x-y coordinates on the PDF plan.