Importing the National Elevation Dataset

Importing the National Elevation Dataset with GRASS.

Data acquisition

Learn how to import the National Elevation Dataset into GRASS via the National Map Access API.

Setup

Start a GRASS session in a new project. Set the coordinate reference system for the project to Louisiana State Plane South using EPSG code 2801.

# Import modules
import sys
import subprocess
import numpy as np

# Find GRASS Python packages
sys.path.append(
  subprocess.check_output(
    ["grass", "--config", "python_path"],
    text=True
    ).strip()
  )

# Import GRASS packages
import grass.script as gs
import grass.jupyter as gj
from grass.tools import Tools

# Create GRASS project
gs.create_project("hilltop", epsg="2801", overwrite=True)

# Initialize GRASS session
gj.init("hilltop")
tools = Tools(overwrite=True)

# Print projection
projection = tools.g_proj(format="shell", flags="p").keyval
print(projection.get("name"))

Set computational region

# Set region
tools.g_region(n=206040, s=205640, e=1023700, w=1022100, res=1)

Install extension

# Install extension
tools.g_extension(extension="r.in.usgs")

Download elevation

# Download elevation data
tools.r_in_usgs(product="ned", ned_dataset="ned19sec", output_name="ned")

Visualize elevation

# Set region resolution
tools.g_region(res=1)

# Supersample elevation
tools.r_resamp_interp(input="ned", output="elevation", method="bicubic")

# Compute contours
tools.r_contour(input="elevation", output="contours", step=0.3)

# Visualize
m = gj.Map(width=1600)
m.d_rast(map="elevation")
m.d_vect(map="contours", color="white")
m.d_legend(raster="elevation", at=(5, 95, 1, 3))
m.show()

Elevation

Export elevation

# Export elevation
tools.r_out_gdal(input="elevation", output="elevation.tif", format="GTiff")

# Export contours
tools.v_out_ogr(input="contours", output="contours.gpkg", format="GPKG")

# Export contours for computer aided design
tools.v_out_dxf(input="contours", output="contours.dxf")