How to represent Typhoon(s) wind speed using Quantum GIS / PostGIS?

Question

I am not completly new to GIS (was taught ArcGIS at Uni) but I would still consider myself (especially compared to all these experts here) a newbie in QGIS or PostGIS.

I want to display the windspeed of typhoons with the help of buffers along their tracks. I used PostGIS to combine the points of the typhoons to Lines ( like in this post). Anyhow, if I buffer the lines, buffer segments from the same typhoon overlap or leave gaps. And I need to change that (Here is a link to a picture showing my problem)

My idea was to create a single line for each typhoon, buffer the line and then split the buffer with the help of my point layer. I need the information on windspeed broken down to the points rather than just an average for the complete typhoon track.

Is there a way to split polygons with the help of point layers? And if not, a way to somehow interpolate the buffer segments that I have right now to close gaps and cut overlapping parts? Doing this manually is not an option at I have to work with typhoon data from 1945-2013.

EDIT: So... if I buffer the lines in Quantum I kind of"solved" the problem of gaps. So I "just" need to interpolate/cut the overlapping parts at the beginning/end of each segment (see picture: http://postimg.org/image/maca8nrc7/ )

Answer 1

I believe you might be working your problem using the wrong tactic.

Not being an expert in Postgis either, I would:

• Put the points data in a Postgis Database;
• Buffer the points according to their windspeed with St_Buffer;

• Agregate the pairs of adjacent polygon using ST_Collect and somekind of point order attribute;
• Pass the result by a St_ConvexHull to create a polygon around them;

• Pass the result by a St_Union, grouping by typhon name or code.

Assuming that my typhon_points table has the columns, "typhon_name", "n_order" (to represent the order of each point in a typhon) and "windspeed", the SQL code to obtain the above procedure would be something like this:

SELECT
    f.typhon_name,
    St_Union(St_ConvexHull(St_Collect(f.geom,g.geom))) as geom
FROM
    (SELECT
        typhon_name,
        St_Buffer (geom, windspeed * 200) as geom,
        n_order
    FROM
        typhon_points) as f,
    (SELECT
        typhon_name,
        St_Buffer (geom, windspeed * 200) as geom,
        n_order
    FROM
        typhon_points) as g
WHERE
    f.typhon_name = g.typhon_name
    AND
    f.n_order = g.n_order - 1
GROUP BY
    f.typhon_name

Hope it helps.