In the second part I will show how to check if latitude or longitude is valid using regular expressions.
First, let's look at example of latitude and longitude in DMSH format, space delimited:
52 22 33.47N 015 42 33.44E
We can write is in general form as:
DD MM SS.ss H DDD MM SS.ss H
and the following must be true:
- DD is between <-90, 90> for latitude and <-180, 180> for longitude
- MM is between <0, 59>
- SS.ss is between equal or grater than 0 and less then 60
and in general format:
ddsddsdd.ddL dddsddsdd.ddL
where d is digit, s is space and L is hemisphere letter (N, S, E, W).
We will take into account that latitude can be without 'leading zeros' in our further deliberations:
1 1 1.44N instead of 01 01 01.44N
There are two options here:
1. To write quite complex regular expression that will take into account all combinations of deg, min, sec e. g.:
- for latitude: if deg is equal 90, min, sec must be equal 0 (90 05 05.55N is not valid latitude)
- for latitude: if deg is between <-90, 90> min might take integer values <0, 59>, sec integer values <0, 59> or float values <0, 60)
2. To write much simpler regular expression that will take into account only general conditions, and if input matches regular expression check if deg, min, sec meet further conditions.
Regular expression to match coordinate in DMSH format, space separated looks like:
regex_dmsh = re.compile(r'''(?P<deg>^\d{1,3}) # Degrees
(\s)
(?P<min>\d{1,2}) # Minutes
(\s)
(?P<sec>\d{1,2}(\.\d+)?) # Seconds
(?P<hem>[NSEW]$)
''', re.VERBOSE)
