Comments (3)
For example, a satellite with a very low elevation (2.5), leads to a weight of:
weight = 1 / Math.pow(Math.sin(elevation * Math.PI / 180), 2) = 517.7
Why 1/...? shouldn't weights be bigger when elevation is higher? it seems counterintuitive
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Hi @ZiglioNZ!
What is used there is actually a cofactor matrix, the inverse of which is used to weight observations in the least-squares solution. Here you can find the corresponding code in the MATLAB version: http://sourceforge.net/p/gogps/code/HEAD/tree/trunk/positioning/least_squares/LS_SA_code.m#l104
DTM values are introduced as "pseudo-observations", with their own observation error (line 699 in this section: http://sourceforge.net/p/gogps/code/HEAD/tree/trunk/positioning/kalman/goGPS_KF_DD_code_phase_loop.m#l665).
You can check also equations (22) and (30) here: https://www.researchgate.net/publication/257836193_goGPS_Open_Source_Software_for_Enhancing_the_Accuracy_of_Low-cost_Receivers_by_Single-frequency_Relative_Kinematic_Positioning
from gogps_java.
I've actually already ported the Matlab code for DTM to Java and have been using it for a few months.
I've used it both with the Google Maps Elevation API (that is probably not precise enough for your needs) and without just to add a soft constraint when I only have 4 satellites.
I haven't found necessarily an increase in precision but when you use the DTM it converges much more quickly. I've found at times with 5 or 6 satellites I need to run up to 400 iterations before the update is smaller than 1m.
See https://github.com/Sirtrack/goGPS/blob/snapshotGPS/src/main/java/org/gogpsproject/ReceiverPosition.java (line 1302)
// Add height soft constraint
double lam = Math.toRadians(this.getGeodeticLongitude());
double phi = Math.toRadians(this.getGeodeticLatitude());
double hR_app = this.getGeodeticHeight();
...
I'd like to merge my contributions into the main project here (thank you for upgrading my access rights).
The problem with this file (ReceiverPosition.java) is it's just too big.
That's why #17
In order to foster innovation (!) we should be able to experiment without risking to break things for everyone.
from gogps_java.
Related Issues (20)
- Ambiguities as state variables HOT 3
- Introduction of LAMBDA method for integer ambiguity resolution HOT 36
- Usage of SP3 ephemeris and satellite clocks
- Use fluent API HOT 2
- Message type in RTCMClient HOT 4
- Partial Rinex files HOT 5
- too old Ephemeris being used HOT 3
- UnhealthyEph and UnhealthySat, breaking change! HOT 7
- Host a Maven repository on github HOT 1
- Is it possible to use this code with the u-blox M8N receiver? HOT 4
- Add ability to pass a list of NavigationProducers
- Handle .z rinex files that are compressed in Gzip format HOT 1
- Position validation of UBX files? HOT 4
- Kalman dops HOT 3
- Rinex observation datas HOT 5
- Real time processing HOT 2
- Set up goGPS_java to real-time porecessing (ublox serial port input data) HOT 3
- Couldn't get messages with Ntrip user. Java GoGPS HOT 3
- Decode 1077 Message HOT 12
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