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6

The problem is poorly documented by authoritative sources for English speakers, despite affecting millions of people on an everyday basis. I've spend the past two days trying to understand the situation and I've created a Wikipedia article about the restrictions on mapping in China and about the China GPS shift problem. Below is the part of my research that ...


3

The course made good (CMG), similar to the speed made good (SMG, sometimes also speed over ground), is the direction a vehicle is traveling, independent of the direction the vehicle is pointing (i.e. the heading of the vehicle). It is measured as the angle from true north that you are traveling. The velocity vector of a vehicle would be the combination of ...


2

There are a variety of reasons why your phone is giving imprecise coordinates when in china, and we can't straight away blame multi-path errors in the Urban canopy for those errors. I feel that you should also know the following before jumping to conclusions. 1) Firstly, As a foreigner, it is illegal to use a GPS device in China 2) Many manufacturers ...


2

For any geometry the units are determined by the spatial reference system. Which you get for a particular geometry with functions ST_SRID(geom). http://postgis.net/docs/manual-2.1/ST_SRID.html (these numbers are in the spatial_ref_sys table and you have to look at the proj4text to see the units description). For geography type coordinates are always x ...


2

I cannot help you explain why the extra digits are truncated. Instead I suggest they do not matter; a decimal co-ordinate with 6 digits is accurate to <0.1m. See this answer: http://gis.stackexchange.com/a/8674/24270 or the wikipedia article: http://en.wikipedia.org/wiki/Decimal_degrees


1

As a fellow GIS-911 professional, if you are looking to maintain the address data, do GIS to MSAG compares, etc... you may also want to look at some of the ArcGIS extensions out there offered by various 911 software companies. These types of tools can be rather helpful because they can expedite/automate certain parts of workflows, they have significant data ...


1

I'm not familiar with the 62 series, but I suspect the issue is similar to or the same as with the 60/76 series. The problem is that GPS unit can only use a specific communications protocol that is not widely supported (Garmin PVT) when connected via USB. It supports a variety of communication protocols over serial, including NMEA, but not over USB. This may ...


1

There are several factors that could be at play here, and I strongly doubt it's strictly an 'urban canyon' issue. For one thing, there may be more sources of interference (beyond things like buildings blocking LoS) in Beijing than in New York. For example the FCC here controls who can use what frequencies and at what strengths and such. Their rules and ...


1

The application should have zero impact on the accuracy of the GPS point data collected. It's entirely dependent on the hardware, as all the apps will tie into the hardware's GPS reporting. The only way the app will have any sort of impact is if it allows for or incorporates averaging readings over time. Most of the other advanced error correction for GPS ...


1

Answer is here :(in 2D you need 2 hyperbola(3 satelites) in 3D you need 3 hyperboloid(4 satelites) Desmond Schmidt is right) http://hayabusa.slovakforum.net/t263-topic#2570 ... sorry it is in slovak language (my english is bad), but pictures and little calculation explain everything, an you can use Google translator.



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