Re: [Qgis-user] Dot Density Symbology
Oops, this was in my Spam folder. It seems that this is the solution to the problem. Thanks a lot! Maria Am 2023/07/28 um 08:04 schrieb Alexandre Neto : Hello Hugh, https://docs.qgis.org/3.28/en/docs/user_manual/style_library/symbol_selector.html#random-marker-fill Check the random marker fill. I believe it's what you are looking for. As you can see in the docs, you can decide how many points you want to insert inside the polygon. This option can be derived of each feature attributes Best regards, Alexandre Neto User Support www.qcooperative.net<http://www.qcooperative.net/> A quinta, 27/07/2023, 18:27, C Hamilton via QGIS-User mailto:qgis-user@lists.osgeo.org>> escreveu: This may not be an answer to your question, but the Density Analysis plugin (https://plugins.qgis.org/plugins/densityanalysis/) will create a uniform set of polygons over an area of interest with a NUMPOINTS attribute of the number of points are contained within the polygon. The NUMPOINTS value can be weighted using some other attribute. It will automatically style the density map as well from a given color ramp. Calvin On Wed, Jul 26, 2023 at 8:06 PM Shinoto, PD Dr. Maria via QGIS-User mailto:qgis-user@lists.osgeo.org>> wrote: Hi, I have a similar research problem, and the dots seem to be a wonderful solution. So, this email does not give any assistance re the original question, just an answer to the question below: Am 2023/07/27 um 03:45 schrieb chris hermansen via QGIS-User mailto:qgis-user@lists.osgeo.org>>: Here's (apologies for the closed source link) an example of the type of map/symbology I'm trying to describe.https://www.arcgis.com/apps/mapviewer/index.html?webmap=30d2e10d4d694b3eb4dc4d2e58dbb5a5 Thanks for any suggestions! What about just shading the polygons using a gray scale? Given that your polygons should generate a uniform density of dots within the area they bound, I don't see value in generating the dots for symbology. The polygon area may vary, as it does in my research (distribution of burials in administrative areas). Therefore, a small area always looks underrepresented as compared to a larger area, and vice versa. I have large administrative areas with low densitiy, but they look well populated even with a very light shade of grey. So I would like to try to find a solution to Chris' problem since the representation with dots is closer to reality than colouring areas. I will report when I found a solution for my use case -- though this may be autumn... Maria ___ QGIS-User mailing list QGIS-User@lists.osgeo.org<mailto:QGIS-User@lists.osgeo.org> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ QGIS-User mailing list QGIS-User@lists.osgeo.org<mailto:QGIS-User@lists.osgeo.org> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ QGIS-User mailing list QGIS-User@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Dot Density Symbology
Good to learn about the various options. The uniform set of polygons is an excellent solution to get a more balanced idea of the density distribution. The problem is that you need to know whether your point is located inside this polygon or not, and as far as I understand, for that, you need to know the geolocation. In my case -- and as it seems in the OP's case -- the problem is that we do not know the exact geolocation but know the location in one administrative unit among many of various sizes. In an example with two units, A with 100sqkm and 200 points, and B with 1000 sqm and 200 points, the shade for density explains the difference, but in my impression, "B" looks like there are more points distributed over a wide area. This is why I like the random distribution of points inside the administrative area; each point may display a specific count of points or, in a next step, a particular density. I hope I got it right; I am inspired by the ArcGIS example the OP posted. Maria Am 2023/07/28 um 02:24 schrieb C Hamilton : This may not be an answer to your question, but the Density Analysis plugin (https://plugins.qgis.org/plugins/densityanalysis/) will create a uniform set of polygons over an area of interest with a NUMPOINTS attribute of the number of points are contained within the polygon. The NUMPOINTS value can be weighted using some other attribute. It will automatically style the density map as well from a given color ramp. Calvin On Wed, Jul 26, 2023 at 8:06 PM Shinoto, PD Dr. Maria via QGIS-User mailto:qgis-user@lists.osgeo.org>> wrote: Hi, I have a similar research problem, and the dots seem to be a wonderful solution. So, this email does not give any assistance re the original question, just an answer to the question below: Am 2023/07/27 um 03:45 schrieb chris hermansen via QGIS-User mailto:qgis-user@lists.osgeo.org>>: Here's (apologies for the closed source link) an example of the type of map/symbology I'm trying to describe.https://www.arcgis.com/apps/mapviewer/index.html?webmap=30d2e10d4d694b3eb4dc4d2e58dbb5a5 Thanks for any suggestions! What about just shading the polygons using a gray scale? Given that your polygons should generate a uniform density of dots within the area they bound, I don't see value in generating the dots for symbology. The polygon area may vary, as it does in my research (distribution of burials in administrative areas). Therefore, a small area always looks underrepresented as compared to a larger area, and vice versa. I have large administrative areas with low densitiy, but they look well populated even with a very light shade of grey. So I would like to try to find a solution to Chris' problem since the representation with dots is closer to reality than colouring areas. I will report when I found a solution for my use case -- though this may be autumn... Maria ___ QGIS-User mailing list QGIS-User@lists.osgeo.org<mailto:QGIS-User@lists.osgeo.org> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ QGIS-User mailing list QGIS-User@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Dot Density Symbology
Hi, I have a similar research problem, and the dots seem to be a wonderful solution. So, this email does not give any assistance re the original question, just an answer to the question below: Am 2023/07/27 um 03:45 schrieb chris hermansen via QGIS-User : Here's (apologies for the closed source link) an example of the type of map/symbology I'm trying to describe.https://www.arcgis.com/apps/mapviewer/index.html?webmap=30d2e10d4d694b3eb4dc4d2e58dbb5a5 Thanks for any suggestions! What about just shading the polygons using a gray scale? Given that your polygons should generate a uniform density of dots within the area they bound, I don't see value in generating the dots for symbology. The polygon area may vary, as it does in my research (distribution of burials in administrative areas). Therefore, a small area always looks underrepresented as compared to a larger area, and vice versa. I have large administrative areas with low densitiy, but they look well populated even with a very light shade of grey. So I would like to try to find a solution to Chris' problem since the representation with dots is closer to reality than colouring areas. I will report when I found a solution for my use case -- though this may be autumn... Maria ___ QGIS-User mailing list QGIS-User@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] QGIS and historical battle
Hi Ciprian, Another archaeologist here. I encourage you to test both paths. (1) Maps from modern to ancient to understand the history of the landscape and the position of the battlefield in that context or (2) Geomorphology from DTM, Hydrology, and additional historical information. We had positive results with LiDAR data in densely forested, mountainous areas that had experienced many changes -- paddy rice fields, buildings, paths -- over the centuries before being abandoned after World War II. With Lidar data, we could create a DTM that revealed small hollows from tunnel kilns that crashed about 1200 years ago. You cannot spot them during field walks, but with the DTM at hand, no problem. A battlefield with digs and earthen barriers should also present some patterns in the DTM that might help you find real places. Of course, this only applies to certain types of battle (though one day with digs may be enough) and whether you have a decent DTM. We used a 20cm grid, but 1m might have been sufficient. The official DTMs from the Japanese government are useless in such research, but I do not know whether you have access to good-quality data in your country. To encourage you! Maria > Am 2023-02-04 um 02:06 schrieb Madry, Scott via QGIS-User > : > > Hi Ciprian. > > There are many examples of such historical/archaeological research. I would > suggest that you get a decent DEM (and generate slope and aspect) and vector > hydrology, as Bernd suggested, but I think the most important will be to find > a series of historical maps of the area. Scan these, or get them in digital > format already if you can, and then georeference the maps to the modern > landscape using either current imagery or you can use Openstreetmap or the > most detailed current governmental data. You don’t say where you are… Once > you have the maps georeferenced, vector digitize the old roadways, bridges, > and other relevant features, so you are working back in time. Start with the > most recent maps and work backwards, and go back as far as you can to the > time of the battle. Then you can start looking at the intervisibility, time > and movement along the roads, and see what locations might best fit your > historical documentary data for what happened. Then you can look on Google > Earth and other imagery (quickmapservices plugin) for vestiges on the > landscape. > > You don’t say what your position is, if you are a professional archaeologist > or simply interested in the history, but do be aware that it is generally > illegal to conduct excavations or ground surveys without proper > archaeological permits and without the permission of the land owner. Cultural > resources laws vary, but it is best to consult the local museum or > archaeologists before any digging. > > Feel free to contact me, > > Scott > > Scott Madry, Ph.D. > Research Associate Professor of Archaeology > The University of North Carolina at Chapel Hill > > Tel 1-919-448-4493 > Email:mad...@email.unc.edu > https://scottmadry.web.unc.edu > Skype: scott madry > > > > >> On Feb 3, 2023, at 9:32 AM, Bernd Vogelgesang via QGIS-User >> wrote: >> >> Hi, >> I'm no archaeologist, but I know that there are quite some of them >> around on this list. >> >> First short answer: yes, of course! >> >> First counter-question: What kind of geodata is already available to you? >> >> Actually, I think you just need 3 data-sets: >> a digital terrain model to find observation spots and valleys >> a vector of rivers to find the confluences >> a point vector of (historic) towns >> >> Unfortunately you did not mention how big the possible region for this >> battle is, so it is hard to guess if it makes sense to create a real >> simulation model, or if places can be identified in a semi-manual way. >> >> I think it would be useful to keep the discussion on the list, so others >> can learn from the example as well. >> Though this is not my business, I am always interested in such kind of >> "riddles". >> >> For a starter: There is the great Visibility Analysis Plugin of Zoran >> Čučković, where you can create a Visibility Index on a terrain data-set >> which I think is exactly meant to identify outlook spots in the >> landscape for a given radius. >> >> Cheers, >> Bernd >> >> >> Am 03.02.23 um 09:20 schrieb Lazanu Ciprian-Cătălin via QGIS-User: >>> Hello, >>> I want to start a project with a great challenge: >>> >>> * first an introduction - a battle between two armies in the medieval >>>period. we have a few pieces of information regarding this battle: >>>the number of soldiers from both armies (army A with ~ 25.000/30.000 >>>soldiers and army B between 50.000 and 100.000 - medieval chronicles >>>have different numbers) and incomplete information regarding the >>>exact place of the battle. all we know is that it was on a river >>>valley and the main battle was regarding controlling a bridge a
Re: [Qgis-user] SRTM problem
Hi, I had the same problem, and Nicolas Cadieux helped me with this hint two years ago: * Quote: It's just the Z factor needed when you make a hillshade when the x an y are in degrees and the z is in feet or meters (like SRTM). You can see it if you choose Hillshade under symbology / render type (for a raster layer). It's basically the length of a degree in meters for latitude. https://www.esri.com/arcgis-blog/products/product/imagery/setting-the-z-factor-parameter-correctly/ * This helped perfectly. Best, Maria > Am 2022-11-29 um 17:17 schrieb Lazanu Ciprian-Cătălin via Qgis-user > : > > Hello, > I have a project and I want to create a map using SRTM as a background. > I upload it ... and looks like that ... > > > but my project area is smaller, so I need to zoom it ... and when I do that, > my SRTM looks like that ... > > > > What can I do so the raster doesn't look so pixelated? > Thank you. > > ___ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Watershed - Catchment area upstream of a point
Hi, I have used SAGA for hydrological analyses following the instructions in Hans van der Kwast's excellent book on hydroloy in QGIS. It worked well in my Japanese environment, but I forgot about the details. Still, Hans van der Kwast also showed how to use GRASS for the same purpose. I tried it, it was more hassle than SAGA so I stayed with SAGA. But, maybe it helps you. There is an instructional video on YouTube: https://www.youtube.com/watch?v=aTYHpft1gus If you did not watch his instructions on using SAGA for that purpose, you may watch his YT videos to check whether you did not forget a step inbetween? Best, Maria > Am 2022-11-09 um 07:04 schrieb Tony Shepherd (FarmMaps NZ) via Qgis-user > : > > Hi All > > I’m wanting to use a DEM/DTM to automatically map the watershed/catchment > area upstream of a known point. > > After a bit of reading, this appears to be a not-so-simple task but > suggestions are to use the “Upslope Area” algorithm. > > In my case, the program fails to finish running, and the message window shows > the following error: > SAGA Version: 7.8.2 (64 bit) > Error: tool needs graphical user interface [Upslope Area] > C:\Users\Tony\Documents>exit > > Questions: > • Does anybody know what that error means? > • Is there another tool/method that is preferable to use? > > Cheers > Tony > > Tony Shepherd | GeoSpatial / Mapping Manager > > Ph 027 435 6193 | E t...@farmmaps.nz | W shepherdphotos.co.nz > > > > > > > ___ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] creating vector layer from slope map with few classes
Hi Richard, this was great, a big thanks to you as well. Classifying was the first problem, and thanks to your step by step explanation, it worked well, easy, quick, producing exactly the results I wished for. Cheers to you and the community, Maria > Am 30.03.2022 um 20:36 schrieb Richard McDonnell : > > Hi Maria, > There is an option to reclassify a raster called Reclassify by Table, which > should create the classified raster you are looking for. > > You can find the Reclassify by Table in the Processing Toolbox, you can then > do the following. > 1. Select the Raster you want > 2. Under Reclassification table click on the button with the three dots. > a. You need to add a row for each class you want, by clicking Add Row > b. For each row set the Minimum and Maximum pixel Values and the new > Value > c. Click OK once you are happy > 3. Set your output no data value, in your case it can be zero > 4. Set Range boundaries as you require > 5. Set your Output data type, I would, based on your description select > Byte > 6. Set location to which you want to save your Raster. > > To polygonise the data then is just a simple matter of using the QGIS > Polygonize tool, which again can be accessed from the Processing Toolbar. Its > default settings should create the output you are looking for. > Hope the above goes some way to helping you. > > Regards, > > Richard > > > > —— > Richard McDonnell MSc GIS, FME Certified Professional > FRM Data Management > > —— > Oifig na nOibreacha Poiblí > Office of Public Works > > Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36 > Jonathan Swift Street, Trim, Co Meath, C15 NX36 > —— > M +353 87 688 5964 T +353 46 942 2409 > https://gov.ie/opw > > —— > To send me files larger than 30MB, please use the link below > https://filetransfer.opw.ie/filedrop/richard.mcdonn...@opw.ie > > Email Disclaimer: > https://www.gov.ie/en/organisation-information/439daf-email-disclaimer/ > > —— > MSc GIS, FME Certified Professional > > —— > Oifig na nOibreacha Poiblí > Office of Public Works > > Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36 > Jonathan Swift Street, Trim, Co Meath, C15 NX36 > —— > M +353 87 688 5964 T +353 46 942 2409 > https://www.opw.ie > > —— > Email Disclaimer: https://www.opw.ie/en/disclaimer/ >> -Original Message- >> From: Qgis-user On Behalf Of Shinoto, PD >> Dr. Maria via Qgis-user >> Sent: 29 March 2022 22:25 >> To: qgis forum >> 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 >> Qgis-user@lists.osgeo.org >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] creating vector layer from slope map with few classes
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 :
>
> 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
>> 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
>>> :
>>>
>>> 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 :
>>>>>
>>>>> 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"
>>>>> Date: 2022-03-29 6:32 p.m. (GMT-04:00)
>>>>> To: qgis forum
>>>>> 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
>>&g
Re: [Qgis-user] creating vector layer from slope map with few classes
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
> :
>
> 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 :
>>>
>>> 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"
>>> Date: 2022-03-29 6:32 p.m. (GMT-04:00)
>>> To: qgis forum
>>> 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
>>> Qgis-user@lists.osgeo.org
>>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
>>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
>>>
>> ___
>> Qgis-user mailing list
>> Qgis-user@lists.osgeo.org
>> 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
> Qgis-user@lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
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Re: [Qgis-user] creating vector layer from slope map with few classes
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 :
>
> 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"
> Date: 2022-03-29 6:32 p.m. (GMT-04:00)
> To: qgis forum
> 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
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[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 Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
