[Tagging] Estimated values for height

Nick Bolten nbolten at gmail.com
Tue Nov 13 22:30:58 UTC 2018


You raise many good points!

My primary concern is in being able to distinguish estimated values that
are "guesstimates" of different types from something where someone took the
effort to use something more precise. Examples:

(1) Jessica is walking along the street and is prompted to estimate a
nearby building's height in meters. They eyeball it and says it's about 3
meters wide and we record it. What's the best way to make a note that this
was acquired through visual inspection so that it can be 'flagged' in later
efforts for measurement with a ruler or laser or offset satellite imagery,
etc?

(2) Bartholomew is armchair mapping an area they are personally familiar
with and wants to estimate the width using JOSM's built-in distance
calculation tool. The tool tells them that it is 3.465839124 meters wide,
and they write that down in the tag. Of course, their error range probably
only justifies writing down "3.7 meters" at best, but we can't ask Bart to
know that for sure. How do we know that Bart's width estimate is only from
aerial imagery + a tool, and temper expectations?

(3) Katie is high tech and uses fancy laser and computer vision to get
centimeter-precision readings. How does she know which places are in need
of more accurate measurements, and how do we know her measurements should
be given the appropriating weighting vs. guessed numbers? i.e., how do we
know which height/width/etc values need accuracy improvements?

On Tue, Nov 13, 2018 at 2:18 PM Graeme Fitzpatrick <graemefitz1 at gmail.com>
wrote:

>
>
> On Wed, 14 Nov 2018 at 06:21, OSMDoudou <
> 19b350d2-b1b3-4edb-ad96-288ea1238eee at gmx.com> wrote:
>
>>
>> I wonder if it’s not.better to accept that *any* measure is an estimate,
>> and let mappers improve the accuracy, just like the drawing of a highway
>> can be a poor or a great estimate, which improves over time as imagery or
>> traces permit improvement.
>>
>> Even if the imagery is of great precision, it’s not a guarantee
>> of.accuracy, as the mapper might be in a hurry or might not particularly
>> care for accuracy, and leave to its successors to improve it.
>
>
> To a certain extent, isn't the height figure that's been entered going to
> show it's perceived level of accuracy?
>
> eg this tree has been entered with a height of 20m, that one over there
> has been entered as 32.5m. To me at least, that would indicate that 20m is
> a (calculated?) guess, while 32.5m was a (relatively?) precise measurement.
>
> &, do we really need to worry about millimetric precision? As has been
> stated many times, trees are constantly changing heights; buildings
> (especially skyscrapers) often have a published height, but does that
> include the TV antenna on the roof?; there is even on-going disagreement
> over the height of Mt Everest
> https://www.nytimes.com/2018/02/03/world/asia/mount-everest-how-tall-nepal.html
>  !
>
> So we, as a bunch of enthusiastic, amateur mappers, are going to be
> pushing things uphill trying to be "exact"! :-)
>
> Thanks
>
> Graeme
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