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Tips and questions relating to the GPS modules from SFE
By ekoy
#135425
have you guys tried any Satellite Predictor or any planning software for GPS??

i tried using http://www.navcomtech.com/Support/Tools ... r/main.cfm
and the software http://www.trimble.com/planningsoftware.html ..

i want to know if you guys use them also and i want to ask if the data u get from the prediction or the result of the software planning is somewhat close to actual?? cause i am not sure if its somewhat accurate enough or might say acceptable or slight error from the actual data.....
#135427
This kind of software bases its predictions on the almanach data, which is broadcast by every GPS satellite and has a validity of several months. A receiver normally stores a copy in its non-volatile memory and uses it to decide which satellites it should search for. So it certainly is accurate enough for that purpose; In practice it may be useful to plan a land survey measurement (looking for an acceptable DOP) although most users don't really care.
#135493
I use planing software only to look for geometry of satellites when I am experiencing accuracy issues. Often I track these down to a very poor geometry of lack of satellites. I would not trust these programs to do the celestial mechanics calculations to the fidelity needed for a solution. That is why one can buy a GPS receiver for $100 or less!
#135602
i see, i am only in need of longitude and latitude data of the GPS receiver.. does it make sense when i am relying to this prediction tool? or is it a waste of time? and also what does ELEVATION MASK mean?.. thanks for your response.
#135608
I am not sure I understand your last question. Having a prediction tool will in no way give you the lat/lon of your unknown location. The prediction tool needs the lat/long/time as an INPUT to tell you which satellites will be were. This is good for determining what your GPS receiver's error will likely be.

Elevation mask allows you to specify what your horizon looks like. If you are out on water, the elevation (vertical angle not height) is pretty much zero. But if you live in the bottom of a canyon, the elevation to your horizon may be 30 degrees. The mask tells the prediction SW what satellites are visible to YOUR receiver due to physical interferences. For the Trimble SW, you can actually provide a different value for each angle of azimuth by dragging your mouse on the hemisphere display.
#135611
ok thanks for your fast reply..

i am using the navcom one since i found it easy to understand.. regarding the lat/long, i am pertaining to the acquired lat/long from the GPS receiver..

i am currently having this project in which in need of lat/long. my workspace would be a soccerfield, in which a UGV will be able to autonomously move around a given point in the soccerfield. so i need this planning tool so that it would not be a waste of time when im on the field where in the satellite available is not good most probably i want to save time by just going to the field knowing that there would be sufficient satellite that can be tracked in the area.

yes i understand what u mean regarding the lat/long but it is not what i meant. in some time when testing my system in the soccerfield i see a big variation on my data collected (i know a soccerfield is just a small area) and i knw its the GPS error ranging from 8 -12 meters i think. i need to have many satellite for more accuracy thats why im choosing the time when it will detect or tracked many satellite in my workspace..

regarding the elevation mask, can u suggest me a value , since i worked at soccerfield with those grass and etc.. (i cant get the elevation mask thing)
thank you for your reply

ekoy
#135641
So you are trying to navigate around a soccer field using GPS and want to make sure you will have a reasonable solution before you test. The planning software will tell you that. Plug in a rough lat/lon for the location and the time and it will show you the number of satellites visible.

I can't help you with your elevation mask number. You will need to bring a protractor/inclinometer/sextant/octant to the soccer field and use it to sight the angle from horizontal to the horizon. That can be used to fine tune the planning software to give you the right number of satellites visible.

There is no need to modify the elevation mask in the GPS receiver UNLESS you have specific information that tells you otherwise. Many are set for 10 degrees. This deletes the pseudo ranges for satellites with a large amount of atmosphere between you and the satellite and hence a lot of propagation errors.

You application just screams of a DGPS solution. Even with SA turned off, a DGPS solution will greatly improve your accuracy.
#135650
hi,
thats good that you get my point.. regarding the elevation mask, from searching the net most probably they use 15 degrees for normal purposes but i dont know the significance of it and also i didnt modify any data or settings in the GPS receiver , i just leave that as is.. most likely the default value in the NavCom field for the elevation mask is 10 degrees but i intend to use 15 degrees.. yes i agree with your last statement with the dgps thing, but unfortunately my data changes from DGPS to GPS from time to time the problem is i cant make it stabilize to DGPS mode only but i already know why.. just need a good condition though..

thanks for the help
#135756
Hi,

Probably you already solved your problem but just for info I use Orbitron:
http://www.stoff.pl/
I know it's a little dated but works well for me.

Regarding your application, I agree with fll-freak. Your application would greatly benefit from DGPS, or RTK. You may use a RTCM enabled receiver (Sparkfun has some) or use a receiver which provides raw measurements and a software like RTKLIB. I assembled the S1315F-RAW and uBlox-5/6T in the past so you might want to have a look at:
http://michelebavaro.blogspot.com/2011/ ... rrier.html
and
http://michelebavaro.blogspot.com/2011/ ... fying.html

Cheers,
Michele