Limit of Capability
This illustration shows the typical
limitation of the four-point map-referencing geometry:-
The points circled in red are those
used to reference the map.
The red grid lines were produced by
creating a text overlay for each of the lat/long intersection points.
RealMaps overlayed this file on the map in accordance with its normal
four-point arithmetic but I coloured them in a paint package to make
them stand out.
I think this illustrates the
strengths and weaknesses of this geometric conversion quite
- It can cope with skew as well as
distortion from non-rectangular lat/long projections.
- It is versatile and easy to apply
since it is not necessary to know the original projection
- Accuracy improves as the area
covered decreases in size - this means that the system works best
for high detail maps.
- For low-detail maps, such as that
illustrated, careful selection of the referencing points can
- The system never accurately
reflects curved lat/long lines.
- On typical maps the longitude
lines are straight and therefore likely to be more accurate in the
Last Updated 25th July
[ Home ]