How do I average a set of rasters?
I have remotely sensed chlorophyll a rasters for several days and I need to get an average of the days represented as one raster layer.
I am using ArcMap 9.2.
[GIS] Averaging set of rasters using Raster Calculator of ArcGIS Desktop
arcgis-9.2arcgis-desktopraster-calculatorspatial-analyst
Related Solutions
First, you should make sure your roads and hydrology feature classes are being rasterized appropriately. You should make sure that the cell size and snap raster (i.e. pixel registration) matches your suitability layer. If you don't, the rasterized roads and hydrology could have much larger cells than intended or be misaligned, leading to undesirable results. Set the snap raster and cell size environment variables in Feature to Raster, as shown below.
Second is the part you were asking about: setting cells in suitability layers as null where the rasterized road (red) and hydrology (blue) layers have non-null values, as shown below.
The easiest way to accomplish this is using Raster Calculator. The Map Algebra expression we want to use is SetNull(~IsNull("hydro.tif")|~IsNull("roads.tif"),"suitability"). Let's break this down step by step.
The
SetNulltool requires two raster layers in the simplest usage. The first is a conditional raster, where cells not equal to zero (equivalent to booleanTRUE) should be set null. The second is the false raster, representing the desired output cell values where the conditional raster is equal to zero (equivalent to booleanFALSE).We want the conditional raster (parameter 1) to be
TRUEif either the roads or hydrology have non-null values andFALSEeverywhere else. TheORoperation is handled by a|(a vertical bar or pipe, the key right below backspace). To find non-null values, we can take the inverse (or booleanNOT) of the null values, which are found using theIsNulltool. To do the booleanNOTin raster calculator we use a tilde~. Combining it all:~IsNull("hydro.tif")|~IsNull("roads.tif").We want the false raster to be our suitability layer, which you can pass in as-is.
Here's the output, with the hydro and roads rasters correctly set null:
I don't know if you have found something, but using grass-GIS you can try all function for landscape analysis.
For example, the r.li.shanon function can be useful for you! And a good point, you can connect Grass in R with the rgrass7 package !
In R it look like :
library(rgrass7)
library(raster)
# initialisation and the a nice dataset
initGRASS(gisBase = "/usr/lib/grass72", home = tempdir(),
gisDbase = "/home/user/grassDB/",
location = "Widou", mapset = "tests", override=TRUE)
execGRASS("r.li.shannon", parameters = list(input="forests", conf="movwindow7" out="forests_shannon_mov7"),
flags = c("overwrite"))
plot(reasRAST("forests_shannon_mov7")) ##plot image
Best Answer
in ArcMap 9.2 using the Raster calculator (Spatial Analyst).
for five raster files: