Help with GPS api to make a tape measure (1.7.10 CC)

I'm kind of good at computercraft and know a bit of lua. I was wondering how I can use Gps (API) and Vector (API) on a advanced pocket computer to make a tape measure (measure the distance between two points). I read on the GPS api "there must be at least 4 computers used as gps hosts which will respond and allow trilateration". Can someone help me code a tape measure program with a simple gui? Maybe the program can have two modes (actual distance between two points) and another mode (it will tell you height difference, x axis difference, and y axis difference).

Hi. First, you need to set up a GPS network. The easiest way (that I know of) is to use this program. Once you have that. You then need to specify a starting point. Once you have specified a starting point you can update your GPS position however often you want and display the distance between the two on the screen.

I won't code a GUI for you, but that is what you put in the actual program :)/>

Exactly which bits are you asking for help with?

The basic idea seems simple enough. Have a button on the APC which records your current position by performing a GPS lookup to one variable. Have another button which performs another lookup, and compares the location you're at to the previously recorded one.

For eg,

local function recordPos()
  savedPos = vector.new(gps.locate())
end

local function comparePos()
  distanceBetween = savedPos - vector.new(gps.locate())
  print(distanceBetween:length())
end

Rig up some functions along these lines to run via touchpoint buttons or something, and you're done.

I was going to post that Touchpoint didn't work on terminals (only monitors), but I decided to update it to work on terminals also. I'll update the OP of the Touchpoint topic with the details.

someone should note, gps is not strictly required if you just want distance from A to B. Any two computers with modems will report the distance between them when recieving rednet messages. Of course, the program could be more convenient running on a tablet where you can just tap a button and walk out the distance to measure, but depending on your particular needs, it might be easier to just plonk a computer down.