bufferqgis
I am trying to create buffers around the Hurricane Sandy path I created in QGIS (points are lat/long).
I have both points from each day she was tracted and the line I created from it with Points2One.
When I go to make buffers around either the line or the points, the buffer takes up the whole screen. Its all just one color.
I have made buffers before but from data I did not create.
Right now all of my projections are set to WGS 84 EPSG 4326.
Creating a View in PostGIS to have a "live buffer" is of course the best choice if you are willing to setup a RDBMS. I was curious to see if you could also get some sort of live buffer without PostGIS, so I gave it a try with spatialite and it works too. The difference is just that it seems that you can't create a View with a different geometry-type in spatialite. I found this inforation here: https://groups.google.com/forum/#!topic/spatialite-users/ZZIPwYt8-uA there was written:
"there is absolutely no way to show a View geometry in spatialite-gis, if the geometry-class isn't exactly the same of the one used for the main-table"
So you have to use a buffer table and three triggers:
CREATE TABLE lines ( id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, name TEXT NOT NULL);
SELECT AddGeometryColumn('lines', 'geometry', 3857, 'LINESTRING', 'XY');
CREATE TABLE lines_buffer (id INTEGER PRIMARY KEY AUTOINCREMENT, gid INTEGER, name TEXT NOT NULL);
SELECT AddGeometryColumn('lines_buffer', 'geo', 3857, 'POLYGON', 'XY');
CREATE TRIGGER "lines_buffer_insert" AFTER
INSERT ON "lines"
FOR EACH ROW BEGIN
INSERT INTO lines_buffer (gid, name, geo)
SELECT new.id,
new.name,
ST_Buffer(new.geometry, 1000) ;
END
CREATE TRIGGER "lines_buffer_update" AFTER
UPDATE ON "lines"
FOR EACH ROW BEGIN
UPDATE lines_buffer
SET geo=(ST_Buffer(NEW.geometry, 1000))
WHERE gid=NEW.id ;
UPDATE lines_buffer
SET name=NEW.name WHERE gid=NEW.id ;
END
CREATE TRIGGER "lines_buffer_delete" AFTER
DELETE ON "lines"
FOR EACH ROW BEGIN
DELETE
FROM lines_buffer WHERE gid=OLD.id ;
END
I havent tested it excessively, but i created, updated and deleted several lines and the buffer was always updated (after refreshing/panning QGIS of course). So this could be an alternative where you have just one spatialite file to store the data and don't have to setup a PostGIS database...
Best Answer
It sounds like you are entering a value in miles or km (ie 10) but the projection is in geographic. The buffer tool will interpolate that as a 10 degree buffer. You will need to do one of two things: