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Enhance elevation profile accuracy with cumulative path distance #1153

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90c0fb1
Enhance elevation profile accuracy with cumulative path distance
Aditya-Dahiya Apr 15, 2025
4673411
Minor correction in proposed code.
Aditya-Dahiya Apr 15, 2025
cfa5a24
Changed assignment operator from "<-" to "="
Aditya-Dahiya Apr 16, 2025
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12 changes: 12 additions & 0 deletions 06-raster-vector.Rmd
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Original file line number Diff line number Diff line change
Expand Up @@ -237,6 +237,18 @@ grid.text("B. Elevation along the line", vp = viewport(layout.pos.row = 1, layou
print(rast_poly_line, vp = viewport(layout.pos.row = 2, layout.pos.col = 1))
print(plot_transect, vp = viewport(layout.pos.row = 2, layout.pos.col = 2))
```
The previous method calculates straight-line distances from the starting point, which may not reflect the actual length of curved or winding paths. To compute true distances along a non-linear route, the coordinates of the segmented points can be used to calculate cumulative distances between successive points:

```r
zion_transect_coordinates = zion_transect |> group_by(id) |> st_coordinates()
point_distances = c(
0,
cumsum(sqrt(rowSums(diff(zion_transect_coordinates)^2)))
)
zion_transect = zion_transect |>
mutate(dist = point_distances)
```
This approach sums the Euclidean distance between each pair of consecutive points along the path, yielding a more realistic elevation profile for non-linear transects.

\index{raster!extraction polygons}
The final type of geographic vector object for raster extraction is **polygons**.
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