[FOSS-GPS] RTKLIB errors and warnings

[Mazahir Poonawalla]

Hi Josh,

Hoping you are doing good. Thank you for all the support. Over the past few
days, I did some experiments. I would like to share and clear some doubts,
if you do not mind.

So, basically, I kept of distance of 14-15m (approx) between the base and
rover. Then I captured data in both "kinematic" and "moving base" modes and
simultaneously I captured data from a third receiver using ublox u-center
which I used for comparison. Now in both the cases, most of the time, the
solution remains in "FLOAT" and there have been only 15%-20% of the time
(in total) that the system remains holds a "FIX" position. What can go
wrong here now?

Secondly, what I am more concerned is the altitude difference between data
from RTKLIB (using base-rover) and u-center (using single receiver). The
altitude varies a lot in RTKLIB in both the modes i.e. Kinematic and Moving
Base. It should remain nearly the same since both base and rover are at a
fixed position as of now.

Thirdly, the baseline too, varies a lot but the average is quite close i.e.
I still get a difference of about 2 meters. The difference between high and
low is quite large, similarly with altitude.

Can you know as to what else can I try? Also, what what is the difference
between moving base and kinematic modes? Difference between "continuous"
and "fix and hold" integer ambiguity resolution? Which one would be more
preferable?

Also I noticed that cycle slip occurs a lot, infact most of the time there
is a cycle slip (as I mentioned above that the solution remains as "FLOAT"
mostly). I have done all my experiments on the terrace under the open sky.
I cannot conclude as what could be the reason?

Hoping to receive a reply from you and taking the discussion forward. Thank
you once again.

Cheers,
Max


On Fri, Feb 7, 2014 at 12:48 AM, Josh Leighton <leighton.josh at gmail.com>wrote:

> a) Those look like fairly standard patch antennas, so I wouldn't be
> surprised if you are unable to achieve a consistent fix.
>
> b) The longer the better.  The accuracy of a proper fix can be on the
> order of cm's, so the accuracy of your base station should probably be at
> least that good.
>
> c) If you're seeing an intermittent fix with low AR ratio, I believe it's
> possibly an incorrect fix.
>
> d) If you don't have a good fix, I suspect changing the base station
> values by a small amount won't do much.  I'm not sure how important the
> accuracy of your base's altitude is, nor do I know what the expected
> accuracy of a good fix's altitude is.  Perhaps others here know more.
>
>
> On Wed, Feb 5, 2014 at 11:45 PM, mazahirp <mazahir.poonawalla at gmail.com>wrote:
>
>> Hi Josh,
>>
>> Thank you for the reply. So basically I need longer distance between the
>> base and rover.
>> I am using - ABRACON APAE1575R2540AADBE-T & ABRACON APAE1575R2540BBDB1-T
>> as
>> my 2 antennas.
>> So, few more doubts:
>> a). Will these antennas do as far as RTK GPS is concerned?
>> b). Will I have to take base readings for so long? Assuming, though base
>> would be at a constant location, but base position could change on a day
>> to
>> day basis. Also, if I log (lat,long and altitude) these values, the data
>> will be very large to average out. Should i use MATLAB for averaging?
>> c). I was getting a "fix" status at certain intervals in static and
>> kinematic mode, but the baseline in the graph was always beyond 5 to 6
>> meters (in both fix and float status).
>> d). If I change the base values in options by a very minimal margin and
>> change its altitude by 10m, still there is no change in the output rover
>> position. The baseline still shows beyond 6m. Also the height/altitude is
>> wrong (when I compare it with a ublox 5t running in u-center placed at
>> same
>> location).
>>
>> Would be really helpful. Thank you once again.
>>
>> Cheers,
>> Max
>>
>>
>>
>> --
>> View this message in context:
>> http://open-source-gps-related-discussion-and-support.1099874.n2.nabble.com/RTKLIB-errors-and-warnings-tp7572812p7572815.html
>>
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