Re: [postgis-users] 2D linestring or multilinestring

2012-06-21 Thread Ed Linde
Also is there an easy way to count the total number of points that are in a
linestring? Cannot find the function to do so.
I want to keep track of how many points are left in a linestring as I go
ahead and do the simplify.

On Thu, Jun 21, 2012 at 10:43 AM, Ed Linde edoli...@gmail.com wrote:

 Hi All,
 I am building a linestring comprising of nearly 1000 points, now I want to
 pick every 10th point and reduce this to a linestring of 100 points!
 I will use ST_linesimplify for this, but now I am wondering if there is a
 measure that shows me the difference between the two linestrings.
 Some measure like the sum of squared errors... I want to know what I
 lose in accuracy by discarding all these points and simplifying my
 line segment. So if my line strings have (x,y) points in them, I would
 like to know the differences in y basically.
 Any ideas for a different kind of measure would be great too. I was
 initially thinking of measuring the distance between each point in the
 original linestring (1000 points) against the new simplified linestring
 and adding their squares... would that work? Just wondering if
 there is a nicer, easier way to do this in Postgis?

 Thanks,
 Ed

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Re: [postgis-users] 2D linestring or multilinestring

2012-06-21 Thread Sandro Santilli
On Thu, Jun 21, 2012 at 11:03:27AM +0200, Ed Linde wrote:
 Also is there an easy way to count the total number of points that are in a
 linestring? Cannot find the function to do so.

ST_NumPoints (OGC, only works with linestring), ST_npoints (postgis extension,
works with any type)

--strk;

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