How to extract values from the Landsat image and plot the spectral profiles of the different materials in R

Question

I have a shapefile for an area that I would like to get the spectral profile of different materials in the area for example water, roads, or vegetation. Something that looks like this?

What would be the best way to do this?

I have loaded the shapefile in r but not sure how to extract the values from the Landsat raster stack.

```{r}
landsat<-stack(B1, B2, B3, B4, B5, B6, B7)
roi <- readOGR("roi.shp")
shapes
```

Thank you in advance

Answer 1

Use the following code

df = raster::extract(landsat,     # raster layer
    roi,                       #shapefile
    fun=mean,         # what value to extract
    df=TRUE)          # return a dataframe

Your raster object and roi should have same coordinate system.