Extract Raster Values from Points

The R blog article encourages me to write this solution to extract Raster values from points in R.

In geospatial analysis, extracting the raster value of a point is a common task. If you have few raster files or few points; you can extract the raster value by overlaying a point on the top of the raster using ArcGIS. What will you do, if you have hundreds of raster files and thousands of points? The easy solution is use loop in Python and ArcGIS. Is loop efficient to use? No. Can loop be avoided? Yes.

Then how? 

Follow the steps:

Step 1: Create a Raster stack or Raster brick of your raster files using “raster” package in R.

For example:

rasStack = stack(raster1, raster2,raster3 …rasterN)

Step 2:  Read point data, and convert them into spatial points data frame.

Sample: pointfile.csv

Point_ID	LONGITUDE	LATITUDE
1	48.765863	-94.745194
2	48.820552	-122.485318
3	48.233939	-107.857685
4	48.705964	-99.817363

For example:

pointCoordinates=read.csv(“pointfile.csv”)

coordinates(pointCoordinates)= ~ LONGITUDE+ LATITUDE

Step 3: Extract raster value by points

For example:

rasValue=extract(rasStack, pointCoordinates)

Step 4:  Combine raster values with point and save as a CSV file.

For example:

combinePointValue=cbind(pointCoordinates,rasValue)

write.table(combinePointValue,file=“combinedPointValue.csv”, append=FALSE, sep= ",", row.names = FALSE, col.names=TRUE)

Step 5: You should get the results as following table.

Result: combinedPointValue.csv

Point_ID	LONGITUDE	LATITUDE	raster1	raster2	raster3
1	48.765863	-94.745194	200	500	-100
2	48.820552	-122.485318	178.94	18.90	10.94
3	48.233939	-107.857685	-30.74	-30.74	-0. 4
4	48.705964	-99.817363	0	110	-0.7

ArcGIS , R