Dear Øyvind,
Indeed I'd call this still a form of triangulation. If you determine the
relative position by (Dx,Dy), you create a rectangular triangle, with
your distance walked being the hypotenuse.
If you have a nice proposal text to add, welcome! So far, I think I have
covered analogue practices.
All the best,
Martin
On 3/5/2021 5:11 PM, Øyvind Eide wrote:
Dear Martin,
I am considering a possible practical counter-example from my own
manual measurement experience. I am not sure if it is relevant but
maybe the first sentence (”Any position measurement is based on
triangulation with multiples distances to reference points and angle
measurements”) should be modified.
I am mapping the location of a boulder. Using a compass and my steps,
fairly well calibrated to one meter, I measure the distance and
direction from my fix point, in this case the spot where a creek is
crossing a path.
The fix point itself is established through stereo aerial photography
and thus, based on a sort of triangulation. But my measurement from
the fix point and the boulder is based on the distance and direction
from the single fix point.
Maybe it makes sense to still call this a triangulation as the compass
shows the direction to the magnetic north.
Whatever can be argued about this, maybe it makes sense to add to the
GPS descriptions a bit more on analogue measurement practices? They
were the basis for a massive amount of museum and cultural heritage
documentation.
All the best,
Øyvind
Am 01.03.2021 um 21:19 schrieb Martin Doerr <mar...@ics.forth.gr
<mailto:mar...@ics.forth.gr>>:
Dear All,
I revise my previous proposal for measuring positions:
Any position measurement is based on triangulation with multiples
distances to reference points and angle measurements. GPS measures
distances to satellites. Distances are Dimensions. If directed
distances use georeferenced directions, i.e. angle to the rotation
axis of earth, etc. angles are again dimensions. Hence, a position
measurement is an evaluation of a combination of multiple associated
distance and angle measurements from a particular spot to certain
reference points of known position in the same reference space. If
stars are used, they constitute (extremely) distant reference points.
Gravity and Earth Magnetic Field also provide reference directions
for angle measurements that do not need a second reference point.
Classical longitude measurements use temporal simultaneity of a
common event with a reference location, which evaluates to an angle.
All methods are fairly complex, but the details are a standard
routine or even hidden in a modern GPS module.
Therefore we argue that position measurement is a specific
(composite) observation which results in a position expression, but
the constituent dimensions may or may not be documented.
Hence, P40 observed dimension (was observed in): E54 Dimension may
not be instantiated.
All position measurements are approximations of other places.
Therefore, they result in a declarative place defined by an E94 Space
Primitive. Since in general we talk about moving reference spaces,
moving things and evolving processes, the time of measurement is
essential. We take it either to be the time-span of the measurement,
or a narrower time-span which covers the contributing time-critical
observations. In essence, this defines a declarative spacetime box
(volume), which again is an approximation. It appears to me that such
an approximation would normally be used to determine parts of the
extent of some instance of Presence by overlap, coverage or containment.
Sxxx Position Measurement
Subclass of: E16 Attribute Assignment
Scope note: This class comprises activities of measuring
positions in space and time. The measured position is intended to
approximate a part or all of the extent of the presence (instance of
E93 Presence) of an instance of E18 Physical Thing or E4 Period of
interest, such as the outer walls of an excavated settlement, the
position of a ship sailing or the start and end of athlete’s run in a
competition. Characteristically, a theodolite or GPS device may be
positioned on some persistent feature. Measuring the position of the
device will yield an approximation of the position of the feature of
interest. Alternatively, some material item may be observed moving
through a measured position at a given time.
A position measurement is an evaluation of a combination of
measurement of multiple associated distances and/or angles (instances
of E54 Dimension) from a particular spot to certain reference points
of previously known position in the same reference space.Often, the
observed constituting dimensions are not documented, or hidden in an
electronic device software.The measured position is given as an E94
Space Primitive corresponding to a declarative place. Together with
the measured time-span covering the time-critical observations it
forms a spacetime volume, which should normally overlap with the
spatiotemporal extent of the thing or phenomenon of interest.
Properties:
Oxx1 determined position (was determined by): E94 Space Primitive
Oxx2 has validity time-span (is position validity for): E52 Time-Span
We may now formulate the approximation to the things of interest, e.g.
Oxx3 overlaps with presence: E93 Presence.
But the time=span of this presence is already implicit in the
time-span of validity.
If we use:
Oxx3 overlaps with presence of: XXXX, we need a property for E18 and
another for E4…
Another use case is when someone wants to determine if she is at a
particular declarative place: Fisherman now mark positions in the sea
with GPS, in order to return to the same spot...
--------------------------------------------
Opinions?
To be discussed!
Martin
--
------------------------------------
Dr. Martin Doerr
Honorary Head of the
Center for Cultural Informatics
Information Systems Laboratory
Institute of Computer Science
Foundation for Research and Technology - Hellas (FORTH)
N.Plastira 100, Vassilika Vouton,
GR70013 Heraklion,Crete,Greece
Vox:+30(2810)391625
Email:mar...@ics.forth.gr
Web-site:http://www.ics.forth.gr/isl
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------------------------------------
Dr. Martin Doerr
Honorary Head of the
Center for Cultural Informatics
Information Systems Laboratory
Institute of Computer Science
Foundation for Research and Technology - Hellas (FORTH)
N.Plastira 100, Vassilika Vouton,
GR70013 Heraklion,Crete,Greece
Vox:+30(2810)391625
Email: mar...@ics.forth.gr
Web-site: http://www.ics.forth.gr/isl
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