Re: [Qgis-user] How to create a QGIS grid but not the usual way
Hi, Thayer. Again, exactly what I wanted to know; you are most kind. Thank you too for advising me about sending a reply to the whole list. I hadn't realized I wasn't doing that. Thank you all who commented on any of several questions I had. This project has come to a successful, rapid conclusion because of the tips you all offered. Have a great day! - John A. On Sunday, May 16, 2021, 05:59:52 PM EDT, Thayer Young wrote: Hi John, You can prevent the warning about no spatial index by creating the index for each layer using the "Create Spatial Index" processing algorithm. Or you can just ignore the warning. If you are certain of the EPSG code for your layers you can use the "Assign Projection" processing algorithm. EPSG 2264 sounds like a good candidate. Reprojecting to UTM Zone 17N should be good also EPSG:26917. You can find both of these tools by entering their names into the search bar at the bottom left of the main QGIS window or at the top of the Processing Toolbox panel. If you have roads and county boundary shapefiles in the same EPSG 2264, you should be able to clip your roads (input) with your county boundary (overlay) using the Clip tool. If you want your roads to overlap the county boundary try reprojecting your Extent polygon to 2264. Another possibility is that there are invalid geometries. You may want to try the Check Validity, Fix Geometries, and or v.clean tools to find and correct invalid geometry. You may also be able to get more information about what is going wrong from the messages panel. There is a toggle button for it in the bottom right of the main QGIS window. You should be able to get a good pdf converter for free or low cost. So you can convert image files and compile them into a single pdf. -Thayer PS Please remember to send responses to the entire mailing list. - Forwarded Message - From: John Antkowiak To: Thayer Young Sent: Saturday, May 15, 2021, 11:06:38 PM EDTSubject: Re: How to create a QGIS grid but not the usual way Hi, Thayer. I may have to ask for a follow-up explanation. I do apologize. I re-projected the file and each layer separately. Now the GUI tells me, as anticipated, that the CRS is EPSG:2264. (Scrolling down through the list of available systems to use, I found this one - which is further identified as NAD83/NC (ftUS) - before I found the UTM choices. So I selected it.) Each layer matches, so that part went as expected. Then I saved the project and restarted QGIS to rule those variables out when the next step failed. Now when I clip the data to a new shapefile, I see the following error: "No spatial index exists for input layer, performance will be severely degraded." I received the same error before re-projecting everything. This happens with both layers I'm trying to clip: the county boundary and the streets. And when I try to add the resulting shapefiles to a new, blank map project, they fail to load. "File unsupported" or words to that effect. I suspect (but I don't know) the problem is that I'm trying to clip the two State-government layers against the grid polygons (rectangles) I created, even though I was able to save that layer as a valid shapefile with a recognized CRS matching that of the State layers. If I have to use UTM instead, how do I know whether it's Zone 16 or 17? (From my professional experience years ago - I have a decent amount of experience but no formal GIS education so I'm no expert regarding projection systems - I thought I remembered the dividing line between the two being in Florida.) Alamance County is centered east to west in the northern half of North Carolina. This step was necessary because I find I can't create an atlas as a PDF and I don't have Adobe to create one from jpegs. I can export a single map to PDF, but not an atlas unless there's a plugin I can go obtain. So I'm trying to create 9 separate maps by clipping the total extent by the gridlines you helped me create (very effectively I might add - thank you again!) Again, both thanks and apologies... - John A. ___ 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] How to create a QGIS grid but not the usual way
Hi John, You can prevent the warning about no spatial index by creating the index for each layer using the "Create Spatial Index" processing algorithm. Or you can just ignore the warning. If you are certain of the EPSG code for your layers you can use the "Assign Projection" processing algorithm. EPSG 2264 sounds like a good candidate. Reprojecting to UTM Zone 17N should be good also EPSG:26917. You can find both of these tools by entering their names into the search bar at the bottom left of the main QGIS window or at the top of the Processing Toolbox panel. If you have roads and county boundary shapefiles in the same EPSG 2264, you should be able to clip your roads (input) with your county boundary (overlay) using the Clip tool. If you want your roads to overlap the county boundary try reprojecting your Extent polygon to 2264. Another possibility is that there are invalid geometries. You may want to try the Check Validity, Fix Geometries, and or v.clean tools to find and correct invalid geometry. You may also be able to get more information about what is going wrong from the messages panel. There is a toggle button for it in the bottom right of the main QGIS window. You should be able to get a good pdf converter for free or low cost. So you can convert image files and compile them into a single pdf. -Thayer PS Please remember to send responses to the entire mailing list. - Forwarded Message - From: John Antkowiak To: Thayer Young Sent: Saturday, May 15, 2021, 11:06:38 PM EDTSubject: Re: How to create a QGIS grid but not the usual way Hi, Thayer. I may have to ask for a follow-up explanation. I do apologize. I re-projected the file and each layer separately. Now the GUI tells me, as anticipated, that the CRS is EPSG:2264. (Scrolling down through the list of available systems to use, I found this one - which is further identified as NAD83/NC (ftUS) - before I found the UTM choices. So I selected it.) Each layer matches, so that part went as expected. Then I saved the project and restarted QGIS to rule those variables out when the next step failed. Now when I clip the data to a new shapefile, I see the following error: "No spatial index exists for input layer, performance will be severely degraded." I received the same error before re-projecting everything. This happens with both layers I'm trying to clip: the county boundary and the streets. And when I try to add the resulting shapefiles to a new, blank map project, they fail to load. "File unsupported" or words to that effect. I suspect (but I don't know) the problem is that I'm trying to clip the two State-government layers against the grid polygons (rectangles) I created, even though I was able to save that layer as a valid shapefile with a recognized CRS matching that of the State layers. If I have to use UTM instead, how do I know whether it's Zone 16 or 17? (From my professional experience years ago - I have a decent amount of experience but no formal GIS education so I'm no expert regarding projection systems - I thought I remembered the dividing line between the two being in Florida.) Alamance County is centered east to west in the northern half of North Carolina. This step was necessary because I find I can't create an atlas as a PDF and I don't have Adobe to create one from jpegs. I can export a single map to PDF, but not an atlas unless there's a plugin I can go obtain. So I'm trying to create 9 separate maps by clipping the total extent by the gridlines you helped me create (very effectively I might add - thank you again!) Again, both thanks and apologies... - John A. ___ 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] How to create a QGIS grid but not the usual way
Hi John, You may want to start by using the QuickMapServices plugin to add a basemap like OpenStreetMap. I suggest OSM because it tends to have administrative boundaries like counties. To make sure that everything is lining up correctly. Then with your extent polygon:You can turn snapping on so that the measure tool snaps to the corners of your extent polygon. View: Toolbars: Snapping Toolbar <-- make sure that this is checked.Then click on the "Enable Snapping" icon, which looks like a red horseshoe magnet with white tips (you can also just press the S key).Then, click on your Extent layer to make it the active layer in the layer panel. Then set the other icons to the right of Enable Snapping as follows: "Active Layer", "Vertex", "6", "px" You should then see that your cursor for the measure tool changes to a magenta square when you hover over the corners (the vertices) of your extent polygon. You may need to reproject or define your projection:It sounds like you probably have an extent that is in state plane, QGIS often has problems recognizing state plane projections. You can try to export your extent to a projection that QGIS understands, for example NAD83 UTM zone 17N or 18N depending on where your county is in North Carolina. Otherwise try the set projection tool. Right click on the extent layer, left click Export then left click Save Features As. In the dialog you can set the projection. -Thayer Date: Sat, 15 May 2021 12:05:53 + (UTC) From: John Antkowiak To: "qgis-user@lists.osgeo.org" Subject: [Qgis-user] How to create a QGIS grid but not the usual way Message-ID: <1021879306.860570.1621080353...@mail.yahoo.com> Content-Type: text/plain; charset="utf-8" Hi. I'm new to QGIS. I've been up all night reviewing the Training Manual and watching tutorial videos looking for someone to address my situation. I'm overtired and I'm sure I'm missing something obvious. I'm trying to create a large-format paper wall map to show all the roads in my county, and I have to create an atlas to do it. For sake of this question, let's assume the county is approximately 19 miles east-west and approximately 28 miles north-south. The key word here is approximately - and I suspect this task requires precision that I don't know how to find.? All the lessons for creating grids from which the atlas will be generated instruct me to do it the same way: specify the desired horizontal and vertical intervals. That's not what I want. What I want is to divide the extent by three, whatever interval that happens to be. And I can't figure out precisely the total dimension, in miles, of the map extent. In case this is relevant: the data layers are projected in?NAD83 / North Carolina (ftUS) but the QGIS GUI at the bottom right says "Unknown CRS."? I created a layer for this exercise - don't ask me to explain how I did it - whose only feature is a rectangle covering the area to be divided. This layer I call "Extent." I try to use the Measure tool to get the exact east-west distance of the polygon. BUT. I have to manually select the start and end points, and I have no confidence that the points I'm selecting precisely match the limits of the polygon because when I measure the north and south horizontal lines, I get two different values. It's a rectangle. The values ought to be the same. Am I going bout this all wrong? How do I create this 3 x 3 grid? Thanks -? John A. -- next part -- An HTML attachment was scrubbed... URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20210515/0731c969/attachment-0001.html> ___ 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] How to create a QGIS grid but not the usual way
Hi. I'm new to QGIS. I've been up all night reviewing the Training Manual and watching tutorial videos looking for someone to address my situation. I'm overtired and I'm sure I'm missing something obvious. I'm trying to create a large-format paper wall map to show all the roads in my county, and I have to create an atlas to do it. For sake of this question, let's assume the county is approximately 19 miles east-west and approximately 28 miles north-south. The key word here is approximately - and I suspect this task requires precision that I don't know how to find. All the lessons for creating grids from which the atlas will be generated instruct me to do it the same way: specify the desired horizontal and vertical intervals. That's not what I want. What I want is to divide the extent by three, whatever interval that happens to be. And I can't figure out precisely the total dimension, in miles, of the map extent. In case this is relevant: the data layers are projected in NAD83 / North Carolina (ftUS) but the QGIS GUI at the bottom right says "Unknown CRS." I created a layer for this exercise - don't ask me to explain how I did it - whose only feature is a rectangle covering the area to be divided. This layer I call "Extent." I try to use the Measure tool to get the exact east-west distance of the polygon. BUT. I have to manually select the start and end points, and I have no confidence that the points I'm selecting precisely match the limits of the polygon because when I measure the north and south horizontal lines, I get two different values. It's a rectangle. The values ought to be the same. Am I going bout this all wrong? How do I create this 3 x 3 grid? Thanks - John A.___ 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
