Re: [Qgis-user] Buffer with qgis : wgs84/mercator world?
Am 10.05.2013 13:48, schrieb image: Hi Marco. Thank you. But my data is a big very long corridor from Berlin to Beijing...;-) If your route comes close to the north pole, EPSG:3408 or EPSG:3575 or EPSG:3576 would fit. These are Lambert Azimutal Equal Aerea projection. Or take EPSG:3035, which fits for Europe. HTH, Andre Joost ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Buffer with qgis : wgs84/mercator world?
How about a Global UTM WGS 84 projection? -- View this message in context: http://osgeo-org.1560.x6.nabble.com/Buffer-with-qgis-wgs84-mercator-world-tp5052504p5052619.html Sent from the Quantum GIS - User mailing list archive at Nabble.com. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Buffer with qgis : wgs84/mercator world?
Hi Marco. Thank you. But my data is a big very long corridor from Berlin to Beijing...;-) -- View this message in context: http://osgeo-org.1560.x6.nabble.com/Buffer-with-qgis-wgs84-mercator-world-tp5052504p5052546.html Sent from the Quantum GIS - User mailing list archive at Nabble.com. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Buffer with qgis : wgs84/mercator world?
HI image, the "meters" in Pseudo Mecator or Google Mercator are not exact meters in reality. Use a better metric projected CRS available for your region of work (where is your data located). You could use the UTM (e.g. 32632 if in Germany) to get far better results. Marco P.S. in Google Mercator the "meters" only next to the equator are approximately meters Am 10.05.2013 13:09, schrieb image: > Thank you. > > I just tried a test to generate a buffer 20 meters from my linear shp(with > pseudo mercator). It works. But when i measure, the buffer is not to 20 > meters but 12/14 meters. > > Could you just make a quick test on your side please? > > Via the interface called Buffer i have entered those parameters: > > Segments for approximation (by default) : 5 > Buffer distance : 20 > > Indeed i'm working on such a small scale and i don't care about small > distortions. > > Could you throw light for me? > > Thanks. > > > > -- > View this message in context: > http://osgeo-org.1560.x6.nabble.com/Buffer-with-qgis-wgs84-mercator-world-tp5052504p5052535.html > Sent from the Quantum GIS - User mailing list archive at Nabble.com. > ___ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-user -- + FOSSGIS 2013, Die Konferenz für Open Source GIS mit OpenData und OpenStreetMap erstmals in der Schweiz! 12.-14. Juni, HSR, Rapperswil, http://www.fossgis.de/konferenz/2013/ + FOSSGIS e.V. die unabhängige Hilfe bei freier GIS-Software und freien Geodaten http://www.fossgis.de + ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Buffer with qgis : wgs84/mercator world?
Thank you. I just tried a test to generate a buffer 20 meters from my linear shp(with pseudo mercator). It works. But when i measure, the buffer is not to 20 meters but 12/14 meters. Could you just make a quick test on your side please? Via the interface called Buffer i have entered those parameters: Segments for approximation (by default) : 5 Buffer distance : 20 Indeed i'm working on such a small scale and i don't care about small distortions. Could you throw light for me? Thanks. -- View this message in context: http://osgeo-org.1560.x6.nabble.com/Buffer-with-qgis-wgs84-mercator-world-tp5052504p5052535.html Sent from the Quantum GIS - User mailing list archive at Nabble.com. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Buffer with qgis : wgs84/mercator world?
Hi I assume there is a misundersanding. I guess Jo assumed that your data is stored in a PostGIS database, which is why he advised to cast the coordinates as GEOGRAPHY. As you seem to be working with shapefiles, this actually doesn't concern you. I would project my data into pseudo-mercator (EPSG:3857) in order to have meter-based coordinates. But I am not sure it will give you the most accurate resutls (don't know how it distorts the surface). How precise does your buffer need to be? If you work on such a small scale (Berlin - Beijing). I would assume that you don't really care about small distortions, do you? Cheers Stéphane -- "Le mot progrès n'aura aucun sens tant qu'il y aura des enfants malheureux" -- Albert Einstein "A journey does not need reasons. Before long, it proves to be reason enough in itself. One thinks that one is going to make a journey, yet soon it is the journey that makes or unmakes you." -- Nicolas Bouvier Photos de voyages, photos de montagne: http://www.henriod.info On Fri, May 10, 2013 at 12:06 PM, image wrote: > Hello, > > Thank you for your reply. But sorry i do not really understand. Could you > make explicit please? > > What do you understand by 'geography'? > > I just make a new test with world mercator & wgs84 also and the result of > the buffers are always big circle . So i suppose that the unity is > radians/degrés... > > My raw linear shp is very long. It is a corridor from Berlin to Beijing. > According to you, which coordinate system i should select in order to > generate a buffer (20kms)? > > Thank you. > > > > -- > View this message in context: > http://osgeo-org.1560.x6.nabble.com/Buffer-with-qgis-wgs84-mercator-world-tp5052504p5052521.html > Sent from the Quantum GIS - User mailing list archive at Nabble.com. > ___ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-user > > ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Buffer with qgis : wgs84/mercator world?
Hello, Thank you for your reply. But sorry i do not really understand. Could you make explicit please? What do you understand by 'geography'? I just make a new test with world mercator & wgs84 also and the result of the buffers are always big circle . So i suppose that the unity is radians/degrés... My raw linear shp is very long. It is a corridor from Berlin to Beijing. According to you, which coordinate system i should select in order to generate a buffer (20kms)? Thank you. -- View this message in context: http://osgeo-org.1560.x6.nabble.com/Buffer-with-qgis-wgs84-mercator-world-tp5052504p5052521.html Sent from the Quantum GIS - User mailing list archive at Nabble.com. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Buffer with qgis : wgs84/mercator world?
If you store in a geography the unit is meters. If you store WGS84 in a geometry it's radians/degrees. Try casting to ::GEOGRAPHY. Jo 2013/5/10 image > Hello, > > i would like generate a buffer (20kms) around my shapefile (line). > > In a 1st time, i tied to do that with wgs84 parameters (for the layer & > project). But the result was a big circle. > > In 2 2nd time, i converted my raw shapefile into wgs 84 mercator world. I > entered this value for buffer-distance : 2. i think the unity is meter. > Could you confirm to me that the unity is meter? > > I succeed in generating a buffer. But when i measure the value of the > buffer > with the measurement tool, the value is 15 kms, no 20 kms. > > Could you throw light for me ? > > Thanks. > > > > -- > View this message in context: > http://osgeo-org.1560.x6.nabble.com/Buffer-with-qgis-wgs84-mercator-world-tp5052504.html > Sent from the Quantum GIS - User mailing list archive at Nabble.com. > ___ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-user > ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
