Hi everybody
I’m a biologist struggling with getting precise GPS coordinates for many a project. We don’t have funding for ‘common’ expensive setup at 15-25000 $, so I’m looking for alternatives.
Thus my question is:
Is the Reach RS as precise (or similar) to the expensive setups regarding accuracy of coordinates? Are all we need really just a Reach RS as groundstation an one as portable receiver? What is the expected accuracy and how can this be accomplished with such ‘cheap’ equipment?
Is it only working if the groundstation is placed on a spot with 100 % known coordinates, because where should we then get those? I have looked in different forums but can’t seem to get a straight answer.
Well…Basically yes.
And no, you dont have to use a base station, VRS ntrip service would work too
How accurat do you need coordinates?
More expensive gear has L2 band and can under certain conditions perform better then L1 only gear.
But Reach has more then fair chance to do many of the same tasks
We are not road engineers, so we are talking within 5 cm precision.
Is this obtainable with two Reach modules (either RS or just the small module) without using correctional services like VRS? Here in Denmark our professional correction service is very expensive per year thus rendering it unusable for us. We really need a sub 5 cm precise setup which is independent of ‘outside’ corrections.
Example of usage could be:
Recording GCP’s (static) for mapping but not necessarily with the one RTK module attached to a drone.
We make precise maps of landuse and analysis on vegetation (and a lot more), along with height models (DTM/DEM).
Artig, du er fra Danmark, da forstår du litt Norsk?
Anyways, Reach could easly be used for your kind of work. You probably have fix points around in your country, like us?
You could use them either RTK or PPK
RTK positioning is relative, which means that Reach RS is really good at calculating the vector from base to rover, this will be precise no matter how you determine base position (within reasonable limits). This vector is aligned with base position in order to produce rover position. If base position is shifted from true position, all rover positions will be shifted by the same distance.
Jeps, norsk er jo næsten det samme som dansk - bare hold dig til gammel-norsk
The fixpoints we have, but are the use of them free? (I gather they are fixed GPS-beams/signal towers).
Ive only heard about them through a gps salesman, where for example GPSnet here in Denmark costs 8000 dkr (1200 $) a year in subscription.
Okay then, but what precision can we expect from the base station itself without correction by fixed GPS beams?
As we don’t really have the need for a rover (just fixed points/GCPs) yet the second module is actually not necessary at this point.
So it’s more a case of: Does reach differ from say a normal handheld GPS which also can get corrected coordinates?
In that case in acts just like a single GPS, a really good one, but accuracy is still in meter range.
Rover is a broad definition, if it is static on a point it is also considered a rover. Rover is a receiver that gets corrections from the base.
And forgot to mention that you can also post-process raw data from Reach, many countries offer free RINEX logs, even when real-time RTCM3 corrections are paid.
Do you have mapservice similar to our http://www.kartverket.no/ ?
We have lot of marks and surveyed point all over the place, free to use. You might have similar
I’ll offer an opinion here based on limited experience with the Reach but quite a bit of experience with similar low-cost L1 band timing chips and RTKLIB.
These lower cost systems can produce the same 2 centimeter level accuracy and precision (2DRMS) as high cost systems for mapping purposes. However, I have found that the higher-cost systems are more robust when confronted with difficult collection scenarios. You’re making a map and collecting the position of real world assets or natural features. Such things are not designed around ideal satellite reception.
The lower cost systems can cope with difficult scenarios, but the onus is on you the collector to fiddle with the RTKLIB settings in real-time in order to tune the system before you collect the point. For example, you may need to change the SNR mask or elevation mask or turn off whole constellations to find the best solution in a problematic spot.
For centimeter “precise” data your base station location can be pretty loose. But for centimeter “accurate” data, you’ll need a good base station with an accurate antenna position and altitude for map making. Any error in base position will cause a reciprocal “shift” in the rover’s position estimates. Here in the U.S. you can use OPUS. Not sure if it works world-wide. Basically, you record data from your base for 24 hours and submit the file to the system. It solves for errors post process and should produce an accurate location and elevation of your base.
Some high end receivers have an automatic calculation mode to register the receiver’s location for a base station mode. They basically collect data for 3-5 minutes then compute a point. This can be helpful if you move the base too frequently. I tried this once with a high-end Hemisphere based system and it produced a point only a few centimeters off the OPUS calculated point. I’ve also tried to write my own “averaging algorithm” for low-cost L1 timing chips but was 1-2 feet off the true location. The problem with averaging is that some root causes of errors are random, producing a nice even distribution surrounding the true location. But some root causes of errors are systematic which tend to introduce bias into the location estimates. So basically, your true location is outside the grouping of point samples.
In summary, the low cost systems can work for map making but requires a lot of study on RTK GNSS positioning techniques. I’m learning new things all the time. If you’re going to attempt map making with low-cost chips, I recommend the Reach over other systems. They have package this system really well and it seems to be getting better almost daily. I’m looking forward to testing it further.
Sorry for butting in on the conversation. I dont not have anything relevant to ask or add to your question, but I saw that you are from Denmark.
Me and my team are in great need to borrow a Reach+ unit for a presentation tomorrow(10/July/2018), and as you may be aware, it is not easy to get a Reach unit over night here in Denmark, so right now I am trying in all places to see if I can borrow one unit for 1 day. I will of course take full responsibility for the unit, so if you could lend us a hand please let know as soon as possible.
Also if anyone else from Denmark has the possibility, we greatly appreciate any help.
Though it’s a long time since this thread was alive, it worth noting what the EUREF network can do for Danes, if talking postprocessing. From the Copenhagen/Sjælland area there are 1 station in Copenhagen, and 1 more across the water 60 km into Sweden.
For Jutland region it is even better with 2 stations, and more across the border with Germany.
But yes, Gpsnet.dk is 12.000 (1600 eur) a year, which way over the top. Currently there are no free NTRIP services in DK, only the Euref stations.
