[postgis-users] Creating points along a line for every second?

[Robert Burgholzer]

Very nice when it actually is that simple :).

rb

On Friday, August 31, 2012, James David Smith wrote:

> Hi Robert,
>
> Thanks for your suggestion - this worked great - and was easier than
> learning how to do loops and similar! (though thanks for the
> suggestions from others too!). I knew just a bit of lateral thinking
> was required!
>
> James
>
>
>
> On 17 August 2012 20:48, Robert Burgholzer <rburghol at vt.edu> wrote:
> > If i understand this right, the series field tells you which second in
> total
> > time of N seconds that it took to move along the line. (end_time -
> > start_time)::float should give you the total time in seconds, and
> > series/total_time should give you the parameter that you want for
> > st_line_interpolate_point
> >
> > HTH
> > r.b.
> > On Friday, August 17, 2012, James David Smith wrote:
> >>
> >> Hi everyone,
> >>
> >> I'm flirted around this problem for a while, so I hope I'm not bein
> >> annoying by being repetative, but I've been tearing my hair out trying
> to do
> >> it. The problem is that I have a file of lines (geometry). in a table
> called
> >> temp4 The format of the table is, simplified,
> >>
> >> line
> >> start_time
> >> end_time
> >> series (I generated this as a count of the seconds difference between
> the
> >> above time fields. I thought it would be useful)
> >>
> >> So for example my table (temp4) might look like this:
> >>
> >> line                    ||    start_time           ||  end_time
>  ||
> >> series
> >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >> line_geom         || 12:07:17                || 12:07:20         ||
> >> 3
> >> line_geom         || 12:07:17                || 12:07:20         ||
> >> 2
> >> line_geom         || 12:07:17                || 12:07:20         ||
> >> 1
> >>
> >> line_geom         || 12:07:21                || 12:07:26         ||
> >> 6
> >> line_geom         || 12:07:21                || 12:07:26         ||
> >> 5
> >> line_geom         || 12:07:21                || 12:07:26         ||
> >> 4
> >> line_geom         || 12:07:21                || 12:07:26         ||
> >> 3
> >> line_geom         || 12:07:21                || 12:07:26         ||
> >> 2
> >> line_geom         || 12:07:21                || 12:07:26         ||
> >> 1
> >>
> >>
> >> Now what I want to do is split the lines into points, with a point for
> >> each second. Evenly spaced along the line. So if the line is 10 metres
> long
> >> and the difference between the start and end is 10 seconds then I want
> to
> >> create 9 points at 10% along the line, 20% along the line, 30% along the
> >> line etc up to a point which is 100% along the line i.e. the end of the
> >> line. I don't need a new point at the start of the line as I have that
> >> stored already.
> >>
> >> So I've been trying something like this, but it's wrong. But maybe along
> >> the right lines.
> >>
> >> SELECT st_line_interpolate_point(line, 1/series::float)) as new_point
> >> FROM temp4
> >>
> >> Taking the first few rows of my data, the percentages along the lines I
> >> want to generate are as follows. I need to find a way to get these
> values
> >> into the st_line_interpolate_line  function.
> >>
> >> line                   || start_time             || end_time      ||
> >> series      ||  percentage along line
> >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >> line_geom        || 12:07:17               || 12:07:20      || 3
> >> ||   0.33%
> >> line_geom        || 12:07:17               || 12:07:20      || 2
> >> || > _______________________________________________
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> >
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