r - Extracting environmental variables at coordinates -


i using r , trying create dataframe containing information on environmental variables @ coordinates (x,y).

currently working matrix altitude data. in form long, lat, altitude.

and spatial points data frame containing x,y coordinates

i have tried use extract function in form:

xyalts <- extract(altvals,xypoints)

however keep getting error:

error in (function (classes, fdef, mtable)  :    unable find inherited method function ‘extract’ signature ‘"matrix", "spatialpointsdataframe"’

can suggest why not work? can extract function not used spatial point data frames?


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