add google elevation source? #28

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1. temospena commented on Apr 25, 2021

   

   temospena

   on Apr 25, 2021

   Last edited by temospena

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   Due the api request limits, it needs another loop to make one request at a time per linestring.

   So, for the full lisbon_road_segments dataset, we can do:

   library(tidyverse)
   library(sf)
   library(slopes)
   library(googleway)
   set_key(Sys.getenv("GOOGLE_KEY"))
   
   
   Roads = st_transform(lisbon_road_segments, 4326)
   # mapview::mapview(Roads)
   
   #a df with only corddinates in WGS84 (google does not like others)
   Roads_coords = data.frame(st_coordinates(Roads$geom))
   names(Roads_coords) = c("lon", "lat", "l")
   
   #a df without geometries
   Roads_xyz = Roads
   Roads_xyz$geom= NULL 
   Roads_xyz$bbox= NULL
   Roads_xyz$geom= NA
   
   #get elevarion per point, and transform each line in a xyz linestring again
   for (i in 1:nrow(Roads)){ 
     google = google_elevation(Roads_coords[Roads_coords$l == i,])
     Roads_coords$elev[Roads_coords$l == i] = google$results$elevation
     Roads_coords$resol[Roads_coords$l == i] = google$results$resolution
     
     line = Roads_coords[Roads_coords$l == i,]
     Roads_xyz$geom[i] = st_as_sf(line, coords = c("lon","lat","elev")) %>% st_combine() %>%  st_cast("LINESTRING")
   }
   
   Roads_xyz = st_as_sf(Roads_xyz, dim = "XYZ", crs=st_crs(Roads))
   
   Roads$slope = slope_xyz(Roads_xyz) #to store the values in the original dataset
   
   summary(Roads$slope)
   #>      Min.   1st Qu.    Median      Mean   3rd Qu.      Max. 
   #> 0.0004856 0.0064922 0.0279617 0.0455289 0.0780702 0.1995000 
   
   summary(Roads_coords$resol) #check average resolution
   #>    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
   #>   1.193   1.193   1.193   1.193   1.193   1.193 
   
   mapview::mapview(Roads["slope"])

   
2. Robinlovelace commented on Apr 25, 2021

   

   Robinlovelace

   on Apr 25, 2021

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   Fantastic, I think that could be the basis of a new function to get slopes from Google's API. Hypothesis: will be faster and more accurate than the current approach that downloads raster DEMs covering the entire area.