On 5/9/2012 12:06 PM, Bob Pawley wrote:
Hi Steve
FYI - I'm not involved in the geography side of Postgis, I'm developing
an application to analyze engineering drawings.
I spend 20+ yrs of my career working with Computervision CAD/CAM
systems, most of that at Computervision in development, so I know a lot
about mechanical drawing, modeling, drafting, and machining.
So, same in shape even
if the shapes are spatially diverse is what I was looking for.
OK, but most of my questions are still valid.
* same shape but different location?
* same shape but scaled, different location?
* same shape but rotated about Z at different location scaled or not?
* don't care about topology
* "same shape" - implies same construction in terms of entities make up
the shape. So:
+-----+-----+ is different from +-----------+ ?
because of the extra node or not?
You might find that is you normalize all shapes into 1.0 x 1.0 unit box
and then do the comparison that this might simplify differences due to
scale.
-Steve W
However, since this function doesn't exist I will need to develop
something.
Thanks for the info.
Bob
-----Original Message----- From: Stephen Woodbridge
Sent: Wednesday, May 09, 2012 8:54 AM
To: postgis-users@postgis.refractions.net
Subject: Re: [postgis-users] Same, similar et al
On 5/9/2012 11:40 AM, Bob Pawley wrote:
Hi
I have two geoms that are similar in shape but don’t share the same
space nor the same size.
Is there a function or method to compare the two shapes in this
situation??
The functions and operators I have found, seem to only look at spatial
sameness.
Or is my only option to spatially transfer and size one geometry to the
other?
Bob
Bob,
I don't think there is anything in PostGIS that does this. A bigger
question in my mind is how do you want to define "similar"? For example:
1. identical but scaled differently?
2. identical but positioned or rotated differently?
3. topologically the same, ie: a coffee mug and donut have the same
topology but not the same shape
4. the same visual presentation but made up of different number of segments
5. and the list goes on and on
-Steve W
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