[postgis-users] PostGIS as a solution for non-geographic x-y or temporal data ?
Lee R
sregdoreel at gmail.com
Wed Aug 27 09:38:07 PDT 2014
On Monday, August 25, 2014 4:46:11 AM UTC-4, Rémi Cura wrote:
>
> You want to map your dimension
> (time, note_pitch) to (X,Y) ?
>
> It seems really difficult to achieve if for instance you would consider a
> C and a C up an octave closer than a C and a D.
>
> And if you consider
> (time,note_pitch) to (X=time, Y = [A-G], Z = [1-8]) ,
> Lot's of function in postgis doesn't work well with Z.
>
Fortunately we can map musical notes as 1-12 instead of A - G, or for that
matter 1-88. As "vectors" the notes can range from -88 to 88 (keys on the
piano), bounded somewhat by abs( vector1+vector2+vector3 ) <= 88.
In other words instead of an X,Y coordinate system, a musical note is 1
dimension (y), time the 2nd dimension (x). Analyzed as a directed path
(geometrically left to right .. ) the query would be analyzing time instead
of a physical "x" coordinate (i.e. longitude).
So if "X" is time & "Y" is pitch, can I quantize time by arbitrarily
discrete amounts & still get usable results? Say for example we establish
the 1/32nd note as being the smallest duration, then everything would be an
integer multiple of that. It's surely not a perfect model, but a cartesian
reduction of a certain problem for quick analyses.
An example of what I'm thinking: Using multilines, it could be possible to
observe where a melody & it's counterpoint harmony cross over. Or draw a
chord as a polygon & see where a melodic line crosses through it.
I wondering what other types of metrics I can derive from a cartesian
geometry?
For instance, I gather PostGIS can find polylines ranked by similarity? If
so this could be superior to my trigram dictionary attack method, or
bothering with an FP-Growth algorithm.
> Moreover, distance between geometry (serei of not ein your case) in
postgis are rather limited to
> _what you can come up with
> _*ST_HausdorffDistance*()
> (you could use R to create your own distances)
TY for the pointer.
I'm very much considering using R as a stored procedure language to work
over these data.
> I'm not an expert but lots of work in GIS rearch is devoted to time
serie, mainly GPS trace (X,Y,Z,timestamp).
> It seems that Grass GIS has a module for it :
http://grasswiki.osgeo.org/wiki/Time_series
Yeh, that's the USACE GIS db. Another thing to look into... :)
Thanks!
--Lee
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