37dbbd0755
Adds variations in GPS coordinate OSD element display: 1. Fractional degrees with 7 digits (default) - 000.0000000 2. Fractional degrees with 4 digits - 000.0000 3. Degrees, minutes, seconds - 000^00'00.0"E 4. Open Location Code (sometimed called Google Plus Code) - 23ABC4R8+M37 Uses Open Location Code library from: https://github.com/google/open-location-code Added support for `STATE(GPS_FIX_EVER)` to differentiate from having a fix now (`STATE(GPS_FIX)`) vs. ever having a fix. Logic change to only display coordinates from the GPS module once a fix has been initially established. This prevents displaying interim coordinates supplied by the GPS while the fix is still being establised as these coordinates can be inaccurate by hundreds of miles. Once a fix is established initially then the coordinates will continue to be displayed even if the fix is lost or degrades in quality. Add logic to "blink" the coordinates if the 3D fix is lost after initially being established. Alerts the user that the coordinate display may be inaccurate or no longer being updated. We want to keep the coordinates displayed to aid recovery if the user loses the fix (like crashing upside down). Replace GPS defines `LAT` and `LON` used throughout the code with the enumeration: ``` typedef enum { GPS_LATITUDE, GPS_LONGITUDE } gpsCoordinateType_e; ``` The Open Location Code option is bounded with `USE_GPS_PLUS_CODE` to allow it to be excluded if needed for targets with limited flash space. It currently fits for F411 but we may have to remove it in the future. |
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| LICENSE | ||
| README.md | ||
| betaflight.h | ||
| betaflight_readme.txt | ||
| olc.c | ||
| olc.h | ||
| olc_private.h | ||
README.md
Open Location Code
Open Location Code is a technology that gives a way of encoding location into a form that is easier to use than latitude and longitude. The codes generated are called plus codes, as their distinguishing attribute is that they include a "+" character.
The technology is designed to produce codes that can be used as a replacement for street addresses, especially in places where buildings aren't numbered or streets aren't named.
Plus codes represent an area, not a point. As digits are added to a code, the area shrinks, so a long code is more precise than a short code.
Codes that are similar are located closer together than codes that are different.
A location can be converted into a code, and a code can be converted back to a location completely offline.
There are no data tables to lookup or online services required. The algorithm is publicly available and can be used without restriction.
Links
- Demonstration site
- Mailing list
- Comparison of existing location encoding systems
- Open Location Code definition
Description
Codes are made up of a sequence of digits chosen from a set of 20. The digits in the code alternate between latitude and longitude. The first four digits describe a one degree latitude by one degree longitude area, aligned on degrees. Adding two further digits to the code, reduces the area to 1/20th of a degree by 1/20th of a degree within the previous area. And so on - each pair of digits reduces the area to 1/400th of the previous area.
As an example, the Parliament Buildings in Nairobi, Kenya are located at 6GCRPR6C+24. 6GCR is the area from 2S 36E to 1S 37E. PR6C+24 is a 14 meter wide by 14 meter high area within 6GCR.
A "+" character is used after eight digits, to break the code up into two parts and to distinguish codes from postal codes.
There will be locations where a 10 digit code is not sufficiently precise, but refining it by a factor of 20 is i) unnecessarily precise and ii) requires extending the code by two digits. Instead, after 10 digits, the area is divided into a 4x5 grid and a single digit used to identify the grid square. A single grid refinement step reduces the area to approximately 3.5x2.8 meters.
Codes can be shortened relative to a location. This reduces the number of digits that must be remembered, by using a location to identify an approximate area, and then generating the nearest matching code. Shortening a code, if possible, will drop four or more digits from the start of the code. The degree to which a code can be shortened depends on the proximity of the reference location.
If the reference location is derived from a town or city name, it is dependent on the accuracy of the geocoding service. Although one service may place "Zurich" close to the Google office, another may move it by a hundred meters or more, and this could be enough to prevent the original code being recovered. Rather than a large city size feature to generate the reference location, it is better to use smaller, neighbourhood features, that will not have as much variation in their geocode results.
Guidelines for shortening codes are in the wiki.
Recovering shortened codes works by providing the short code and a reference location. This does not need to be the same as the location used to shorten the code, but it does need to be nearby. Shortened codes always include the "+" character so it is simple to compute the missing component.
- 8F+GG is missing six leading characters
- 6C8F+GG is missing four leading characters
Example Code
The subdirectories contain sample implementations and tests for different languages. Each implementation provides the following functions:
- Test a code to see if it is a valid sequence
- Test a code to see if it is a valid full code Not all valid sequences are valid full codes
- Encode a latitude and longitude to a standard accuracy (14 meter by 14 meter) code
- Encode a latitude and longitude to a code of any length
- Decode a code to its coordinates: low, high and center
- Shorten a full code relative to a location
- Extend a short code relative to a location