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When using the heatmap plugin, I am getting some insanely large numbers for the cell size field when setting the radius to 5000. I know that rows and columns are related to cell size x and cell size y, but I don't know how exactly.

Anyway, when I click OK and run the plugin, I get "nan" as a layer on the raster. Check the pictures below to see what I mean.

enter image description here

enter image description here

  • What's the input layer CRS? – underdark Mar 9 '15 at 20:02
  • The input layer is a set of about 300 points. It's funny, because when I first ran the tool, I got a gray map but didn't like the default values used. Then, after I went back, the defaults were set to what you see above. – Chris Mar 9 '15 at 20:22
  • That doesn't answer my question :-) – underdark Mar 9 '15 at 20:31
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    CRS = coordinate reference system, should be able to find by right-clicking the layer and going to properties and checking one of the tabs. Could be geographic (something like WGS84, common for GPS points or lat/long coordinates in degrees), or projected (like UTM Zone #, coordinates are usually xy in meters). Given your xy values I'm guessing you have geographic degrees and want projected ft or m. Rows and columns define the number of pixels in the raster, while xy size determine how big one pixel is. Thus the two together can give the total size/area of the raster and is how they're related. – Chris W Mar 9 '15 at 21:19
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    BTW, you should edit your question using the button at the lower left of it, under the tags, to provide additional information or clarification requested in comments. You can use a comment to notify the requester you've update like this: @underdark may be able to help more now. Note you can only use one @ notification per comment. – Chris W Mar 10 '15 at 21:17
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If you did not reproject the data at any point of the preprocessing process, you can overwrite the contents of your result Shapefile's .prj file with the original .prj file content. It's just a text file, so open in a text editor and overwrite the content.

In case you did reproject the data at some point, I suggest redoing the filtering and splitting process while paying attention to the CRS. Depending on the filtering you applied, it might even be possible to just use the original file, go to Layer Properties | General | Query and set the filter there. Then run the heatmap tool.

  • I did as you suggested with the .prj files to no avail. I will see if I can mess with the filtering when I split the points and then see if the heatmap will run. – Chris Mar 11 '15 at 17:50
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    So I was able to run the heatmap (finally). I took the original data, selected the points I wanted for a subset using the attribute table, and used a right click save-as to save these points as a new file by specifying the CRS as WGS 84 (I do not know why this worked, but even if it was not the original CRS, the difference between is not noticeable for my personal application) – Chris Mar 16 '15 at 18:34
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I had a similar issues. I was able to fix them with a combination of two things.

  1. Making sure I had no data points with a value of NULL for latitude and longitude.
  2. Paying attention to the ratio of radius to cell size. If I wanted a smaller radius, I needed to reduce my cell size... by increasing my number of rows.

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