[Crm-sig] Issue 388 measuring position

Martin Doerr martin at ics.forth.gr
Fri Mar 5 18:47:59 EET 2021


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 <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.
>>
>> 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:martin at 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: martin at ics.forth.gr
  Web-site: http://www.ics.forth.gr/isl

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