Dear All,
A friend shared an ENVI made file for NDVI 1998- 2012. I would like to use R to
read the file in and extract NDVI values over some points shapefile.
The file attached is a snapshot of the file contents as previewed in ArcGis.
I have managed to get my way around a bit. See below my code....might need a
little cleaning. Still new!
###################################Start#######################
library(raster)
mybrick8 <-
brick("E:/Jr/SLF/HealthyFutures/ShapeFiles/NDVI_1km/aNTONndvi/SPOT_VGT_filtered_Ethiopia.img")#read
NDVI file
names(mybrick8)
dim(mybrick8)
plot(mybrick8, y = 1)
plot(mybrick8, y = 2:13,col = terrain.colors( length(seq(0,250, by = 50))-1),
breaks= seq(0, 250, by = 50), axes = T,xlab = 'Longitude', ylab =
'Latitude',
cex.lab = 1, cex.axis = 1 )
mybrick9<-((mybrick8*0.004)-0.1)# the NDVI file is in reflectance values, so
extracting actual NDVI values
names(mybrick9)
plot(mybrick9, y = 1)
mymap5 <-
readShapePoints('Y:/D/HealthFutures/Neaural/25kmptsethiopia.shp')
plot(mymap5, add = T)
NDVIspot041998_072012_25kmPtsETH121998072013 <- extract(mybrick9, mymap5, #
summary over the points of interest
fun = mean, small = T,
na.rm = T,
layer = 1,
n = 1000)
write.csv(NDVIspot041998_072012_25kmPtsETH121998072013, file =
"Y:/D/HealthFutures/Neaural/NDVIspot041998_072012_25kmPtsETH121998072013.csv")
###################################End#######################
The data however is in decadal; every month has 3 readings, for example
V1_1998_04_01, V1_1998_04_11, and V1_1998_04_21 for the month April 1998. I
would wish to get the average per month. How do I go about this?
Is it possible to write out single files at a selected time period, as raster,
to a folder that I could later perform some geo-processing tasks?
Regards,
Jusper
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