[OSM-newbies] A square is a square is a square is a square .... (Was:Re: Entering building sizes in meters into one of the editors)

Norbert.J.Girardi nobbes at girardis.de
Wed Aug 13 20:18:07 BST 2008


Eric Ladner schrieb:
> On Mon, Aug 11, 2008 at 4:07 PM, Norbert.J.Girardi <nobbes at girardis.de> wrote:
>> Hello to all,
>>
> ...
>> Is there a way to draw the "ways" for these buildings using width and
>> length entries like with a normal drawing editor?
>>
> 
> One of the problems with that is all the coordinates are stored in
> lat/lon form.  Computing precise measurements is a pain and converting
> back and forth from distance to lat/lon is problematic and error prone
> (earth is an oblate spheroid, etc.).  Even doing regular vector math
> on some of the ways comes up with errors because of round off problems
> (dealing with coordinates that only have differences of a millionth or
> less difference between them).
> 
> In general, I'd say nothing really needs to be THAT accurate.  Get the
> buildings close, then call it a day.  :)
> 
> 
I agree with your statement about accuracy, but:

Have a look at the attached square.osm file.

At lat='49.50218451651357' lon='8.604470651502528' I tried to draw a 
square of 20 by 20 meters as precisely as JOSM permitted.

Have a look at what JOSM shows. This is not MY idea of a square ;-)

Both, measurement plugin and the information line at the bottom of the 
JOSM screen agree that this "building" is 20x20 meters.


So, this is probably the reason why the buildings I drew are so crooked 
and completely out of proportion.

Norbert
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