I am using grass-6.4.2 for generation of heat maps of crime data. For testing purpose, I created a vector layer from my places shapefile which is a point data.The places shapefile contains more than 3000 data.I used v.kernel command for generation of raster map as follows:

g.region rows=20 cols=20
v.kernel input=Places@PERMANENT output=raster1 stddeviation=0.001

But the output was a rectangle. I increased the stddeviation value step by step to 10000. The output has Maximum value in output: 1.591528e-11. but the raster image is completely wrong. Please help me in solving this issue.

I checked with rows=600 and columns=600 with a standard deviation of 1000. Here is the output I got:

(Thu Nov 15 11:05:14 2012) Command finished (0 sec)                             
(Thu Nov 15 11:06:05 2012)                                                      
v.kernel input=Places@PERMANENT output=raster3 stddeviation=10000               
STDDEV: 10000.000000
RES: 1324.680000    ROWS: 600   COLS: 600

Writing output raster map using smooth parameter=10000.000000.

Normalising factor=648263501.877776.
Maximum value in output: 1.589441e-09.
(Thu Nov 15 11:06:07 2012) Command finished (2 sec)

All I get is several rings with different colors radiating from the center.

Thanks in advance.

  • 1
    Please explain how you know the result "is completely wrong" and in what way it is erroneous. It is striking that you use only 20*20 = 400 cells to represent 3000 points. Another interesting aspect is the stddeviation value of 0.001. If the data are in meters, that is far too small; if the data are in degrees, you will get incorrect results because you haven't projected them. You might like to review the related threads, How to interpret GRASS v.kernel results? and How do you use GRASS's v.kernel?.
    – whuber
    Nov 14 '12 at 13:43
  • 1
    Re the edit: This sounds like the output is correct. What happens when you set the standard deviation to a value somewhere between 1 and 10? (Note that the output indicates you set it to 10,000, not 1000.)
    – whuber
    Nov 15 '12 at 6:09

Yes, the parameter name is confusing. Hence, upon discussion and a ticket, 'stddeviation' has been renamed to 'radius' with the kernel radius in map units.

  • ... hence it is solved for GRASS 7. In GRASS 6 it cannot be renamed for consistency reasons. Hope this has solved the problem.
    – markusN
    Jan 16 '13 at 23:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.