Hi, Thanks for your advice and offer to help. Yesterday, I had a QGIS crash, today, I restarted, and the problems with polygonize (GDAL and QGIS) were gone. Yesterday I could not create a virtual layer and no stored layer, today, both are no problems. Sorry for causing trouble -- but I have to say, that gave a lot of confidence.
I still have some warnings, particularly with Python code involved (I do not yet use it myself directly). But I will solve these step by step, for the time being: Polygonize is not a problem any more. Cheers, and thanks as always, Maria > Am 30.03.2022 um 19:54 schrieb Nicolas Cadieux <[email protected]>: > > Hi, > > If you’re comfortable with python you can always follow the introduction here. > > https://pcjericks.github.io/py-gdalogr-cookbook/raster_layers.html#polygonize-a-raster-band > > You can also send me a link to the file and I could try on a windows box. > You could check bug reports to see if it’s been reported also. > > Nicolas Cadieux > https://gitlab.com/njacadieux > >> Le 29 mars 2022 à 21:04, Shinoto, PD Dr. Maria >> <[email protected]> a écrit : >> >> Nicolas, >> >> Tried it once again, short names and reasonable paths do not work. I am on >> Mac, QGIS 3.24, will test some reasons for the failure tomorrow again and >> report. Thanks for your advice, >> >> Maria >> >> >> >>> Am 30.03.2022 um 09:34 schrieb Nicolas Cadieux via Qgis-user >>> <[email protected]>: >>> >>> Hi, >>> >>> "Polygonize" should work well to vectorize the raster classes. If you have >>> problems with the file name, try simplifying the file name to the bare >>> minimun like c:\temp\toto.shp if you're on Windows. Make sure you have no >>> spaces or accents in the path (this includes the user path of your >>> operation system). Notice that there are two polygonize algorithm. One is >>> from QGIS and one is from GDAL. Try both. They are probably both based >>> on GDAL but one (probably the QGIS one) may have an easier time with >>> accents, spaces or special characters like '\n'. >>> >>> Good luck >>> >>> Nicolas >>> >>> On 2022-03-29 7:51 p.m., Shinoto, PD Dr. Maria via Qgis-user wrote: >>>> Hi Kirk, >>>> >>>> that was helpful, thank you. >>>> >>>> I am not yet where I need to be, but so far I could create two classes >>>> with the formula found in the docs >>>> (https://docs.qgis.org/3.10/en/docs/user_manual/working_with_raster/raster_analysis.html) >>>> along this line: >>>> >>>> `("slope@1" < 50) * 1 + ("slope@1" >= 50) * 2` >>>> >>>> At this moment, my biggest problem is creating the vector file, the window >>>> claims that the file name is too long. This cannot be the case, and the >>>> directory itself should be OK. So now I am trying to get this done, and >>>> then I will test three classes, which I did not get working up to now >>>> either. >>>> >>>> If there are easy answers to these two questions, I would be pleased, >>>> otherwise, I will try tomorrow. >>>> >>>> Thanks a lot, >>>> Maria >>>> >>>> >>>> >>>>> Am 30.03.2022 um 07:14 schrieb kirk <[email protected]>: >>>>> >>>>> Hi Maria. >>>>> The symbology does not reclassify the underlying raster, it just changes >>>>> the way it is displayed. Use the raster calculator to generate a new >>>>> raster with the Classes you require. The native qgis calculator works >>>>> well. You can find it in the upper word menu under raster. Once you >>>>> have your raster reclassified, you can then convert it to a vector format >>>>> >>>>> Kirk Schmidt >>>>> >>>>> >>>>> >>>>> Sent from my Galaxy >>>>> >>>>> >>>>> -------- Original message -------- >>>>> From: "Shinoto, PD Dr. Maria via Qgis-user" <[email protected]> >>>>> Date: 2022-03-29 6:32 p.m. (GMT-04:00) >>>>> To: qgis forum <[email protected]> >>>>> Subject: [Qgis-user] creating vector layer from slope map with few classes >>>>> >>>>> Hi, >>>>> >>>>> I have created a slope map from a DTM. >>>>> >>>>> I have limited the symbology to three meaningful classes and wish to >>>>> create a vector layer with polygons of three classes from that. The >>>>> conditions are One-Channel-Pseudocolor, Channel1 (Gray), interpolation >>>>> discrete, modus "fortlaufend" -- not identical interval or quantile, 3 >>>>> classes with values <=20, 20 - 40, > 40. >>>>> >>>>> The classes show up in the layer design panel symbology tab, but the >>>>> layer browser still (thankfully!) shows the greyscale ramp. >>>>> >>>>> I wish to create a vector layer with polygons from the 3 classes. >>>>> >>>>> All solutions I have looked up work under slightly different condition. >>>>> After all I do not know how to get the data of the DTM into three classes >>>>> like "Flat-Gentle-Steep"; I think the vectorization should work easily >>>>> then. >>>>> >>>>> Can anybody hint me to a solution? >>>>> >>>>> >>>>> Thanks and best wishes, >>>>> Maria >>>>> _______________________________________________ >>>>> Qgis-user mailing list >>>>> [email protected] >>>>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >>>>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user >>>>> >>>> _______________________________________________ >>>> Qgis-user mailing list >>>> [email protected] >>>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >>>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user >>> >>> -- >>> Nicolas Cadieux >>> https://gitlab.com/njacadieux >>> >>> _______________________________________________ >>> Qgis-user mailing list >>> [email protected] >>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user >> _______________________________________________ Qgis-user mailing list [email protected] List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
