# Newbie question about base coordinates

My goal is to use a rover to survey a site and get RELATIVE locations for the objects on the site. In other words, x,y,z distances from a surveyed point to the base location at that particular site. Not really interested in the exact lat/long/alt of the spot on the planet, just how far it is from the base position.

Can I just enter 0,0,0 for the lat long and altitude for my base Reach module coordinates and then the solution will be providing “relative” values rather than absolute location on the planet?

To put a purpose to the application, I plan on surveying water ski slalom and jump courses using RTK. I would arrive on the site and mark a spot that I would use for my base station. I would then take the rover to each slalom buoy on the lake and get the x,y,z location of that buoy.

If I needed to re-survey the site, I simply put the base back on my marked spot and all my relative distances should be the same. This should give me repeatable values from one survey to the next.

Is my thinking wrong about the way the x,y,z solution format works in the Reach RTK? Do I HAVE to use a real set of base coordinates?

Hi Terry,

Everything that you said is correct, but you have to enter base coordinates that are not 0,0,0, but approximate location. You can find them by configuring Reach as rover->single first, writing down the coordinates and restarting with them in base mode. This will be done automatically in the future.

Wow, thanks for the instant response!
I am trying to wrap my head around the difference between using 0,0,0 and “approximate”…

I can see that it would be a good idea from a GPS perspective to know where you are to know what satellites the GPS should be looking for, but is there a technical difference or is it just that using 0,0,0 looks to the Reach like the value has not been entered and therefore is invalid?

Does it matter how accurate the “approximate” values really are for my application? Could I use one set of values for all over North America?

The reason I am asking is I am wondering if I can make a “turnkey” setup to use at water ski sites so they don’t have to figure out or enter anything, they just set it down and use it and every time they come back to the same site and put the base in the same marked spot, they get the same results.

It just breaks the math in positioning if you enter a far away location, so you need to have an approximate location. I do not have the exact cutoff value, but it should be within 10s of meters. We are going to add this feature where base determines the approximate location automatically on the power up soon.

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Thanks. So to be within 10s of meters I need like 4 decimal places in the lat long fields… I am going to assume that altitude is less fussy (may be a bad assumption)

When you add this feature my newbie suggestion would be 2 options for base coordinates.
Manual - enter coordinates manually… fastest startup time when you already know.
Auto - fill in an option for the number of GPS readings it should average to get your base coordinates. That way you decide how long this will take on powerup depending on your accuracy requirements…
Remote - Some way to have the base coordinates pulled or pushed from a remote connection, tcp, wifi, 3DR radio, … that’s just pie in the sky thinking from someone with not enough experience yet to know if this is realistic.

Hi Igor, how accurate will be absolute position of base station measured in rover mode?

Depending on your Satelite cosntelation, and especially if you have SBAS available.
Without SBAS: best 3-5m

Thanks!
I will get some notification if SBAS will be available? What about absolute accuracy with SBAS? It’s gonna be a way better?

If position of my base station will have absolute accuracy let’s say 3-5m and I will use rover to measure a bunch of point all of them will have accuracy related to base station in 1-2cm level, but absolute position can be shifted 3~5m?

Am I right?