4 ms·

there's something I don't understand, not coming from a mapping background: sixth decimal place of latitude/longitude is already down to about 10cm precision, s

there's something I don't understand, not coming from a mapping background: sixth decimal place of latitude/longitude is already down to about 10cm precision, so using two 8:24 fixed point would give you comparable precision with half the encoding length than this format (using two fixed points dword encoded straight in base 32). why these encoding prefer to use space partitioning more than encoded coordinates?

ColinWright 7y ago
I thought this was comprehensively covered in the linked document. Specifically, it says: ... latitude and longitude provide an exact location, are used internally by GPS and satellite navigation devices, and are sometimes printed on paper maps. However they are rarely seen on city or street maps and are difficult for people to use. They consist of long and complicated numbers, have different ranges (-90 to 90 vs. -180 to 180) and need to be used in a specific order. (To express a reasonably precise position requires between 14 and 18 characters.) A system of encoding location information into a short and an easy to use code would solve these problems. It goes on to say: Easy to use: The codes must be short enough to be remembered and used. This means that they need to be shorter than latitude and longitude and about the same length as a postal code or telephone number. The symbols used to make up the code should not include characters that can be easily confused (e.g., 1 and I, 8 and B, 2 and Z, 5 and S etc.) Does this not answer your question?
- LoSboccacc 7y ago
  this doesn't really answer the question, because encoding the latitude/longitude number in base32 fixed point makes them short, readable and memorizable as much as it would encode them in this scheme, and as I said above, would even result in a shorter string at comparable precision. once they're letter, people wouldn't care if internally are mapped to raw numbers or hierarchical quads, a program would do the conversion back and forth anyway for both systems. so for example the vatican's cupolone center under a b32 fixed point lat-encoded notation would be KUDRL6677SLE at full precision while it's opencode equivalent would be 15 letters (except for the shortening, which could be done here as well)
  - ColinWright 7y ago
    I've just glanced again at the linked document and your comments seem to me to be adequately addressed there, so I'm not sure what you're suggesting/asking. The characters that are used in Open Location Codes were chosen ... to avoid, as far as possible, Open Location Codes being generated that included recognisable words. ... Open Location Codes are encodings of WGS84 latitude and longitude coordinates in degrees. ... The first approach ... provides codes that can be visually compared, or alphabetically ordered to determine if they are close to each other. The second approach allows the code area to be refined using only a single digit. If the entire code was generated using the second approach, it would result in codes that could not be reliably compared visually. I thought the benefits were explained quite clearly, so I'm at a bit of a loss as to what you're suggesting.
    - LoSboccacc 7y ago
      all encodings are arbitrary, to some degree. this scheme of using hierarchical partitioning gives two shortcoming: degenerate area at poles and variable area at fixed precision. using raw degrees doesn't. why is the former preferred than the latter by mappers? it can't be just 'because it's letter and not numbers' because, as demonstrated above, that's just encoding data in memoizable forms, which doesn't depend on the choice of the mapping scheme. being able to visually compare codes also isn't enough of a differentiator, since nearby places would have nearby encoding even in a raw "latitiude/longitude to base-32" scheme, and if it's important that variation is on the least important digit one could just encode lat:long bits interleaved, so that the least significant bits of each are rightmost. the question I have is not about the encoding, as shown it's easy to create an encoding with the desired characteristics that uses the degrees by themselves without the partitioning and its issues, the question is why use these area based system with all the deformation they have instead of properly encoded degrees, what's the benefit to cartographers etc.
  - slyall 7y ago
    I'm not sure why you want fixed point. Some of the reasoning behind them going with base20 is here: https://github.com/google/open-location-code/blob/master/docs/olc_definition.adoc#open-location-code https://github.com/google/open-location-code/blob/master/doc... * 10 characters can represent a 14x14 meter area suitable for many buildings * Using a number base of 20 makes some calculations easier * We could identify a 20 character subset from 0-9A-Z that doesn’t spell words.

ColinWright 7y ago

I thought this was comprehensively covered in the linked document. Specifically, it says: ... latitude and longitude provide an exact location, are used internally by GPS and satellite navigation devices, and are sometimes printed on paper maps. However they are rarely seen on city or street maps and are difficult for people to use. They consist of long and complicated numbers, have different ranges (-90 to 90 vs. -180 to 180) and need to be used in a specific order. (To express a reasonably precise position requires between 14 and 18 characters.) A system of encoding location information into a short and an easy to use code would solve these problems. It goes on to say: Easy to use: The codes must be short enough to be remembered and used. This means that they need to be shorter than latitude and longitude and about the same length as a postal code or telephone number. The symbols used to make up the code should not include characters that can be easily confused (e.g., 1 and I, 8 and B, 2 and Z, 5 and S etc.) Does this not answer your question?

LoSboccacc 7y ago
this doesn't really answer the question, because encoding the latitude/longitude number in base32 fixed point makes them short, readable and memorizable as much as it would encode them in this scheme, and as I said above, would even result in a shorter string at comparable precision. once they're letter, people wouldn't care if internally are mapped to raw numbers or hierarchical quads, a program would do the conversion back and forth anyway for both systems. so for example the vatican's cupolone center under a b32 fixed point lat-encoded notation would be KUDRL6677SLE at full precision while it's opencode equivalent would be 15 letters (except for the shortening, which could be done here as well)
- ColinWright 7y ago
  I've just glanced again at the linked document and your comments seem to me to be adequately addressed there, so I'm not sure what you're suggesting/asking. The characters that are used in Open Location Codes were chosen ... to avoid, as far as possible, Open Location Codes being generated that included recognisable words. ... Open Location Codes are encodings of WGS84 latitude and longitude coordinates in degrees. ... The first approach ... provides codes that can be visually compared, or alphabetically ordered to determine if they are close to each other. The second approach allows the code area to be refined using only a single digit. If the entire code was generated using the second approach, it would result in codes that could not be reliably compared visually. I thought the benefits were explained quite clearly, so I'm at a bit of a loss as to what you're suggesting.
  - LoSboccacc 7y ago
    all encodings are arbitrary, to some degree. this scheme of using hierarchical partitioning gives two shortcoming: degenerate area at poles and variable area at fixed precision. using raw degrees doesn't. why is the former preferred than the latter by mappers? it can't be just 'because it's letter and not numbers' because, as demonstrated above, that's just encoding data in memoizable forms, which doesn't depend on the choice of the mapping scheme. being able to visually compare codes also isn't enough of a differentiator, since nearby places would have nearby encoding even in a raw "latitiude/longitude to base-32" scheme, and if it's important that variation is on the least important digit one could just encode lat:long bits interleaved, so that the least significant bits of each are rightmost. the question I have is not about the encoding, as shown it's easy to create an encoding with the desired characteristics that uses the degrees by themselves without the partitioning and its issues, the question is why use these area based system with all the deformation they have instead of properly encoded degrees, what's the benefit to cartographers etc.
- slyall 7y ago
  I'm not sure why you want fixed point. Some of the reasoning behind them going with base20 is here: https://github.com/google/open-location-code/blob/master/docs/olc_definition.adoc#open-location-code https://github.com/google/open-location-code/blob/master/doc... * 10 characters can represent a 14x14 meter area suitable for many buildings * Using a number base of 20 makes some calculations easier * We could identify a 20 character subset from 0-9A-Z that doesn’t spell words.