QUALITY OF THE
HORIZONTAL S. REF. (GeM+ button)
Section [SPATIAL_REFERENCE_SYSTEM:QUALITY] (REL
file)
In this section are found the quality parameters of the horizontal reference system. More information on the structure of the quality parameter keys can be found in the Quality - Parameters section.
In particular, this section reincorporates the "pos'n error" entry of the older documentation files as this value is converted into an RMS measure of the positional accuracy parameter that indicates the relative horizontal position measured by the RMS.
This means that, if in the older documentation file we find:
pos'n error : 12.7
then the planimetric quality will show:
Parameter: Positional accuracy
Indicator: Relative horizontal accuracy
Measure: RMS
Type of values: Double precision real
Measured value: 12.7
Measurement units: m
(or the units given by the "ref. units :" key in the older documentation file)
For multi-band layers it is possible to document a value for this key for each band different from the general value (see the Thematic Information section). For this reason GeM+ has a radial button (when dealing with multi-band layers) that allows the display of either the general data or the selected band data (this choice is made using the pull-down menu and the forward and back buttons in the upper part of the GeM+).
Note that it is useful to be able to show the units of each quality measure because they may be different from the units of the horizontal reference system. (eg. The reference system could measure in degrees but the quality measure might be in kilometres).