srtm

README

srtm

Go library for reading Shuttle Radar Topography Mission (SRTM) HGT files

Written on pure golang. Based on github.com/jda/srtm and inspired geojson-elevation and node-hgt

Compare testing results (tested on Intel Core i3-7100, 8GB memory, SSD, elevation/srtm services run inside docker with port forwarding).

	Memory usage at start, MB	Memory usage active phase, MB	docker slimmed image, MB	rps (siege trans/sec)
node.js elevation-service	40.44	73.96	161	834.00
golang srtm-service	2.196	22.69	13.5	3008.51

Siege run from command

siege -t 5S -c 500 --content-type "application/json" 'http://localhost/ POST {"type":"LineString","coordinates":[[8.399786506567509,47.3439995300119],[8.401089653337102,47.34382901539513],[8.402392791687875,47.34365848600848],[8.403695921619205,47.343487941852196],[8.404999043130463,47.343317382926415],[8.406302156221027,47.34314680923133],[8.407605260890275,47.34297622076714],[8.408908357137577,47.342805617534005],[8.410211444962314,47.342634999532144],[8.41151452436386,47.3424643667617],[8.412817595341588,47.34229371922288],[8.414120657894879,47.34212305691586],[8.415423712023102,47.34195237984083],[8.41672675772564,47.34178168799798],[8.418029795001864,47.34161098138748],[8.419332823851153,47.34144026000951],[8.42063584427288,47.34126952386427],[8.421938856266422,47.34109877295194],[8.423241859831155,47.34092800727269],[8.424544854966458,47.3407572268267],[8.425847841671704,47.340586431614206],[8.427150819946267,47.34041562163533],[8.428453789789527,47.340244796890275],[8.42975675120086,47.340073957379225],[8.43105970417964,47.33990310310238],[8.432362648725245,47.33973223405991],[8.43366558483705,47.33956135025199],[8.434968512514432,47.339390451678824],[8.436271431756767,47.33921953834058],[8.437574342563435,47.33904861023746],[8.438877244933805,47.338877667369644],[8.440180138867259,47.338706709737295],[8.441483024363173,47.338535737340614],[8.44278590142092,47.33836475017978],[8.444088770039883,47.33819374825498],[8.445391630219433,47.3380227315664],[8.446694481958948,47.3378517001142],[8.447997325257806,47.337680653898616],[8.449300160115381,47.33750959291979],[8.450602986531052,47.33733851717791],[8.451905804504195,47.33716742667317],[8.453208614034189,47.336996321405756],[8.454511415120406,47.33682520137584],[8.455814207762229,47.33665406658363],[8.45711699195903,47.33648291702928],[8.458419767710186,47.33631175271298],[8.459722535015079,47.33614057363493],[8.46102529387308,47.33596937979531],[8.46232804428357,47.3357981711943],[8.463630786245924,47.335626947832075],[8.463638463275133,47.3356259387696]]}'

Support 1-arcsecond and 3-arcseconds hgt-tiles.

Provide web-service as elevation-service (like github.com/asmyasnikov/elevation-service) with allow CORS requests, auto-download zipped hgt-tiles from imagico service, unzipp and persist hgt-tiles in user-defined tile directory.

Environment variables:

• HTTP_PORT - http port of web-service (default 80)
• TILE_DIRECTORY - directory of hgt tiles (default ./data/)
• LRU_CACHE_SIZE - LRU cache size (default 1000)
• LOG_LEVEL - logging level
• WWW - prefix of handlers (default "")
• DEBUG - boolean flag for debug handlers with pprof (default false)
• EXTRACT - boolean flag for auto extracting hgt.gz files (after extracting remove archive, default false)

Install and usage:

• from sources

# go get github.com/asmyasnikov/srtm/srtm-service
# mkdir data
# HTTP_PORT=80 TILE_DIRECTORY=./data LRU_CACHE_SIZE=1000 srtm-service &

• from docker

# mkdir data
# docker run -itd --rm -v $(pwd)/data/:/data/ -p 80:80 -e HTTP_PORT=80 -e TILE_DIRECTORY=/data -e LRU_CACHE_SIZE=9 -e LOG_LEVEL=debug amyasnikov/srtm-service:latest

• in sources

package main

import (
	"github.com/asmyasnikov/srtm"
	"log"
    "time"
)

func main() {
	data, err := srtm.New(9, "./data/", time.Minute)
	if err != nil {
        log.Fatal(err)
		return
	}
	defer data.Destroy()
    point, err := data.AddElevation([]float64{
        8.399786506567509, // longitude
        47.3439995300119, // latitude
    })
    if err != nil {
        log.Fatal(err)
    }
    log.Printf("Lat: %.7f, Lng: %.7f, Elevation: %.1f", point[1], point[0], point[2])
}

Documentation

Index

• Variables
• func IsHGT(fname string) bool
• type LatLng
  • func Meta(fname string, size int64) (sw *LatLng, squareSize int, err error)
  • func Read(fname string, bytes []byte) (sw *LatLng, squareSize int, elevations []int16, err error)
  • func ReadFile(file string) (sw *LatLng, squareSize int, elevations []int16, err error)
  • func (ll *LatLng) String() string
• type SRTM
  • func New(lruCacheSize int, tileDir string, expiration time.Duration) (*SRTM, error)
  • func (d *SRTM) AddElevation(point []float64) ([]float64, error)
  • func (d *SRTM) AddElevations(geoJson *geojson.Geometry, skipErrors bool) error
  • func (d *SRTM) Destroy()
  • func (d *SRTM) Size() uint64
• type Tile
  • func (t *Tile) GetElevation(ll LatLng) (float64, error)
  • func (t *Tile) LRU() time.Time

Variables

var ErrInvalidCoordDegrees = errors.New("invalid lat/lon degrees")

ErrInvalidCoordDegrees is returned when latitude/longitude is unparsable or otherwise invalid

var ErrInvalidHGTFileName = errors.New("invalid HGT file name")

ErrInvalidHGTFileName is returned when a HGT file name does not match pattern of a valid file which indicates lat/lon

Functions

func IsHGT

func IsHGT(fname string) bool

IsHGT returns true if fname appears to be a SRTM HGT file

Types

type LatLng

type LatLng struct {
	Latitude  float64
	Longitude float64
}

LatLng represents a location

func Meta

func Meta(fname string, size int64) (sw *LatLng, squareSize int, err error)

Meta reads meta information of SRTM file

func Read

func Read(fname string, bytes []byte) (sw *LatLng, squareSize int, elevations []int16, err error)

Read reads elevation for points from a SRTM file

func ReadFile

func ReadFile(file string) (sw *LatLng, squareSize int, elevations []int16, err error)

ReadFile is a helper func around Read that reads a SRTM file, decompressing if necessary, and returns SRTM elevation data

func (*LatLng) String

func (ll *LatLng) String() string

type SRTM

type SRTM struct {
	// contains filtered or unexported fields
}

SRTM is a struct contains all internal data

func New

func New(lruCacheSize int, tileDir string, expiration time.Duration) (*SRTM, error)

New make initialization of cache

func (*SRTM) AddElevation

func (d *SRTM) AddElevation(point []float64) ([]float64, error)

AddElevation returns point with 3 coordinates: [longitude, latitude, elevation] Param tileDir - directory of hgt-tiles Param point - [longitude, latitude]

func (*SRTM) AddElevations

func (d *SRTM) AddElevations(geoJson *geojson.Geometry, skipErrors bool) error

AddElevations returns geojson with added third coordinate (elevation) Param tileDir - directory of hgt-tiles Param geoJson - geojson for processing Param skipErrors - if false AddElevations use premature exit (on first bad point in geojson). if true all points will be process but bad point will not to be contains elevation coordinate

func (*SRTM) Destroy

func (d *SRTM) Destroy()

Destroy clean all internal data

func (*SRTM) Size

func (d *SRTM) Size() uint64

type Tile

type Tile struct {
	// contains filtered or unexported fields
}

Tile struct contains hgt-tile meta-data and raw elevations slice

func (*Tile) GetElevation

func (t *Tile) GetElevation(ll LatLng) (float64, error)

GetElevation returns elevation for lat/lng

func (*Tile) LRU

func (t *Tile) LRU() time.Time