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

[Robert Burgholzer]

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              ||   0.67
> line_geom        || 12:07:17               || 12:07:20      || 1
>    ||   100%
>
> Sorry for the long explanation. Hope that you understand where I am coming
> from. Grateful for any ideas please!
>
> Thanks
>
> James
>


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