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
  1. Decimal degree system (dD)
  2. 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.
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.

Conversion to decimal degree system

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:
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.
In principle, only the following five input patterns are permitted, whereby only one letter from each of the square brackets may be used.

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. Spatial Precision