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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