# [postgis-users] Simple Point Density Surface

Doug_Newcomb at fws.gov Doug_Newcomb at fws.gov
Wed Apr 25 11:12:02 PDT 2012

```James,
Looking at  -
http://webhelp.esri.com/arcgiSDEsktop/9.3/index.cfm?TopicName=How%20Point%20Density%20works
.  Why not convert the raster cell centers to points , do a query on the
point layer for a square centered on the raster derived point  whose
dimensions are given by the number of tiles in your neighborhood.  return
the number of points divided by the area of the square.  ( neighborhoods
are usually odd numbers of cells, 3x3, 5x5, etc so you have an equal
number around the center cell)  .

The kernel optoin requires more thought

Doug

Doug Newcomb
USFWS
Raleigh, NC
919-856-4520 ext. 14 doug_newcomb at fws.gov
---------------------------------------------------------------------------------------------------------
The opinions I express are my own and are not representative of the
official policy of the U.S.Fish and Wildlife Service or Dept. of the
Interior.   Life is too short for undocumented, proprietary data formats.

JamesH <james.holmes at newcastle.ac.uk>
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04/25/2012 01:15 PM
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Subject
[postgis-users] Simple Point Density Surface

Hi all,

I am looking to take a point dataset and generate a point density raster
in
PostGIS, similar to the ArcGIS Point Density tool in Spatial Analyst.

What I believe I need to do is to define a neightbourhood around each
output
raster cell centre and calculate a density value for each pixel based on
the
number of points that fall within that neighbourhood.

Ideally to recreate the same results, I would like to define a
neighbourhood
with a radius of 8 cells - most likely a square neighbourhood.

I have been considering this for a while but I really cannot understand
how
to acheive this.

Any advise or help would be greatly appreciated.

Kind Regards,
James Holmes

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