[Crm-sig] Issue 388 measuring position
martin at ics.forth.gr
Fri Mar 5 18:47:59 EET 2021
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,
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
> All the best,
>> Am 01.03.2021 um 21:19 schrieb Martin Doerr <martin at ics.forth.gr
>> <mailto:martin at 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.
>> 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...
>> To be discussed!
>> 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
>> Email:martin at ics.forth.gr
>> Crm-sig mailing list
>> Crm-sig at ics.forth.gr <mailto:Crm-sig at ics.forth.gr>
> Crm-sig mailing list
> Crm-sig at ics.forth.gr
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,
Email: martin at ics.forth.gr
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Crm-sig