tkrajina / go-elevations

SRTM parser for golang

SRTM parser for golang

go-elevations is a parser for "The Shuttle Radar Topography Mission" data.

It is based on the existing library for python srtm.py

Usage

package main

import (
	"fmt"
	"net/http"

	"github.com/tkrajina/go-elevations/geoelevations"
)

func main() {
	srtm, err := geoelevations.NewSrtm(http.DefaultClient)
	if err != nil {
		panic(err.Error())
	}
	elevation, err := srtm.GetElevation(http.DefaultClient, 45.2775, 13.726111)
	if err != nil {
		panic(err.Error())
	}
	fmt.Println("Višnjan elevation is", elevation)
}

go-elevations is a parser for "The Shuttle Radar Topography Mission" data.

It is based on the existing library for python srtm.py

License

This library is licensed under the Apache License, Version 2.0

go-elevations's Issues

Elevation returns NaN

I'm getting lots of NaNs from this point...

An example:

Lat: 30.404229
Lon: 79.547245

Locals in the debugger at that point are:

row = {int} 714
column = {int} 656
i = {int} 858170
byte1 = {uint8} 128
byte2 = {uint8} 0
result = {int} 32768

Any ideas why?

When a query falls between points- averaging?

When a query falls between two/more points, which point does your code select? What/how might you suggest to grab one/more points and average?

Code doesn't run- missing client

Cool library, but unfortunately doesn't seem to run as stated in README.md (called example.go), here are the errors

./example.go:10:39: not enough arguments in call to geoelevations.NewSrtm
	have ()
	want (*http.Client)
./example.go:14:40: not enough arguments in call to srtm.GetElevation
	have (number, number)
	want (*http.Client, float64, float64)```

Downloads broken?

Hi, I was using the library for quite some time and it always worked seamlessly.
Thank you for all your work.

Today, when I wanted to get the elevation of some coordinates, I got 2024/03/21 21:46:33 Invalid file N45E013 in the logs and the result was NaN.
Maybe the mirror changed again?

When I find some time, I might look into it myself.
Thanks again.

SRTM Website No Longer Providing Data

I think the USGS https://dds.cr.usgs.gov/srtm/ is no longer delivering data non-authenticated HTTP requests.
Every request seems to return a 404 not found.
Example: https://dds.cr.usgs.gov/srtm/version2_1/SRTM1//Region_01/N40W114.hgt.zip returns a 404.

Looks like the tests are failing because of this. Granted, am just running go test and didn't really debug further.

--- FAIL: TestGetElevation (0.00s) srtm_test.go:51: Invalid elevation for (45.277500, 13.726111): NaN, but should be 246.000000 srtm_test.go:51: Invalid elevation for (-26.400000, 146.250000): NaN, but should be 301.000000 srtm_test.go:51: Invalid elevation for (-12.100000, -77.016667): NaN, but should be 133.000000 srtm_test.go:51: Invalid elevation for (40.750000, -111.883333): NaN, but should be 1298.000000

My current solution is to download the data from https://search.earthdata.nasa.gov/ (NASA Shuttle Radar Topography Mission Global 3 arc second V003) and putting it into the cache directory with the filename that the go-elevations library is looking for. The earthdata does require a free account to access the downloads.

Earthdata produces a script that downloads each file individually.
Here's an example of one of the new download links.
https://e4ftl01.cr.usgs.gov//DP133/SRTM/SRTMGL3.003/2000.02.11/S34W059.SRTMGL3.hgt.zip
The script itself is just a bash script that uses curl to retrieve the data. It's authentication is archieved via a netrc file, so just basic authentication it looks like.

Here is some highlights from the script:

setup_auth_curl() {
    # Firstly, check if it require URS authentication
    status=$(curl -s -z "$(date)" -w %{http_code} https://e4ftl01.cr.usgs.gov//DP133/SRTM/SRTMGL3.003/2000.02.11/S34W059.SRTMGL3.hgt.zip | tail -1)
    if [[ "$status" -ne "200" && "$status" -ne "304" ]]; then
        # URS authentication is required. Now further check if the application/remote service is approved.
        detect_app_approval
    fi

fetch_urls() {
  if command -v curl >/dev/null 2>&1; then
      setup_auth_curl
      while read -r line; do
        # Get everything after the last '/'
        filename="${line##*/}"

        # Strip everything after '?'
        stripped_query_params="${filename%%\?*}"

        curl -f -b "$cookiejar" -c "$cookiejar" -L --netrc-file "$netrc" -g -o $stripped_query_params -- $line && echo || exit_with_error "Command failed with error. Please retrieve the data manually."
      done;
  fi
}

So in theory, I guess the library could be updated to use a new urls.json, and with a username + password configured in the client creation helper? But I'm unsure of this host being active all the time: e4ftl01.cr.usgs.gov

Anyway, just posting my findings. Hopefully what I wrote makes sense! Definitely a bummer if they did take down the SRTM service, the library has worked great thus far!