GeoCruncher
A central problem when importing data are different geographic coordinate formats. For this reason a QC-module (named
GeoCruncher) was developed. In this module, various allowed input formats are recognized, checked and converted into the
desired output format, here in decimal degrees. If an automatic conversion fails, the process is aborted.
Short summary of geographic coordinate formats
There are two systems to be separated
- Decimal degree system (dD)
- Hexagesimal systems (GMS - Degrees Minutes Seconds)
Decimal degree system
The decimal degree system consists only of a floating point number
and the information whether the number is latitude or longitude.
- Latitude (North/South): -[0 - 90]
- Longitude (West/East): -[0-180]
The hemispheres do not belong in the dD system. The hemisphere is
indicated there by an implicit (missing) plus sign or an explicit
minus sign. Frequently used hybrid forms of GMS and dD are not
allowed. In particular, the following characters are not allowed in
the decimal degree system:
Hexagesimal system
In the hexagesimal system the same information is encoded in three numbers degrees (D), minutes (M) and seconds (S)
including hemisphere [N: North, S: South, W: West, E: East or O: Ost (in German)]. The hemisphere [N/S: latitude, W/E():
longitude] determines whether longitude or latitude is meant.
Value ranges
The following maximum values are valid for D, M and S.
- Latitude: D 90°, M60', S60".
- Longitude: D180°, M60', S60"
Conversion to decimal degree system
- D° M' S"
- 1° = 60' = 3600"
- 1' = 60"
- D = D + M/60 + S/3600
Total maximum values for degrees
A geographic coordinate where the sum of degrees, minutes and seconds is greater than 90 (for latitude) or 180 (for
longitude) is not allow (e.g. Lat: 89° 60' 1"). Each component of the classical hexagonal system can also be defined
more precisely as a floating point number (recognizable by an imagined d for decimal). The single and total amount rule
applies and the following parts are omitted as follows:
- D° M' dS" [NSWE(O)]
- D° dM' [NSWE(O)]
- dD° [NSWE(O)]
Additional information: A value in the format dD° [NSWEO] can
represent the same content as a value in the format [- ] dD, but
these are two different types of encoding.
Input format tests
All of the above rules and circumstances will be checked for every
incoming geo reference. In particular, the following applies.
- The specification of the hemisphere is obligatory (but it can be at the beginning or at the end).
- A plus sign is never allowed as a sign in a geographic coordinate.
- When using decimal gegrees/minutes/seconds, a decimal point is
mandatory, e.g. N3° is not allowed, it should be N3.0° or
N3°0'0".
In principle, only the following five input patterns are permitted, whereby only one letter from each of the square
brackets may be used.
- D° M' S" [NSWE(O)]
- D° M' dS" [NSWE(O)]
- D° dM' [NSWE(O)]
- dD° [NSWE(O)]
- [- ] dD
Explicit hemisphere test
Since the data model makes it known which geographic coordinates (as input data) are longitude or latitude, the use of
the correct hemisphere specification is checked even when using the classic hexagesimal system. For example, 80° 12' 3"
W is correct if it is known from the data model that it actually represents the longitude. .
However, if it is known from the data model that it must be a latitude the geographic coordinate is rejected as
false.
Spatial precision
Here comes another little refresher on what influence precision has on georeference.