A GSTAT library of R was used to generate a grid size of (i) 10 x 10 m and (ii) 10 x 5 m running from an Easting of 299677 m to 301297 m and a Northing of 5737278 m to 5738128 m. This resulted in an interpolation grid of 14,018 and 27,873 data points respectively. This indicates that 10 x 5 m has higher resolution than 10 x 10 m by having more data points to be interpolated (27,873). Could anyone guide me on how to determine the point density by cell for each of this grid size?
I'm not sure I understand what are the point from which you wish to retrieve cell density. Are those sampled data of some kind?
If so typically a point set is given by coordinates X and Y plus whatever variable or variables it has. From that you can transform your point real coordinates (X,Y) into "grid" coordinates (I,J) with this:
I = (X-first grid coordinate in x-axis)/(size of grid cell in x-axis)
J= (Y-first grid coordinate in y-axis)/(size of grid cell in y-axis)
From here you can make a new grid of counters so for every node in G(i,j) you get:
G(i,j) = G(i,j) + 1 , for every sample it exists on cell.
Is this what you are looking for?
Hi,
You have just to determine how many cells you have got on your grid. Then, the interpolated points divided by the number of cells is the point density.
Agree with Mohammed Taaouati, and if you want to differentiate by cell, you can group the points by cell by finding any point located within 4 coordinates that are the limit of the cell you are interested in... and then you can look at density variation in space...etc... but your question is rather unclear.
I too agree with Taaouati and Gomez. Simply the number of point features of your interest in the study area divided by the total number of grids/cells in the study area will give you the point density.
at this link (http://www.digital-geography.com/create-point-density-raster-in-qgis/#.VHWsdzGG98E) you can find the procedure to calculate points density with QGIS (open source software). You also need to download the plugin Heatmap.
Hi, I'm agree with Lupiano Valeria, QGIS has a powerful plugin to compute a raster point density. The plugin name is Heatmap. The plugin allow you to chose the radious as well as the function with whom compute the density. You have even the possibility to set up the rate of decay. For example see:
http://qgis.spatialthoughts.com/2012/07/tutorial-making-heatmaps-using-qgis-and.html
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