Yuichi S. Hayakawa

レーザ距離計とGNSSを用いた現場でのお手軽地形図作成法

早川裕弌東京大学空間情報科学研究センター

2011.11.26 GIS-Landslide Workshop 3rd

Yuichi S. Hayakawa

Introduction

Detailed topographic maps/data are necessary as the basic material for geoscientific field surveys

Yuichi S. Hayakawa

How to get a topo map?Freehand Classical methods High-tech methods

easy

inaccurate accurate

effortful

Yuichi S. Hayakawa

Disadvantages of high-tech methods

• High resolution satellite images and/or airphotos are still expensive. In some countries their acquisition is limited due to military reason.

• Data processing of satellite/airphotoimages for topographic data is often cost-ineffective (time & money).

• Airboren/terrestrial laser scanning is also time-consuming or restricted in rural areas abroad.

Yuichi S. Hayakawa

Yuichi S. Hayakawa

Use of portable devices: LRF and DGNSS

• LRF; laser range finder• DGNSS; differential global navigation

satellite system (incl. GPS, GLONASS) Quick acquisition of accurate maps

• Advantages: portability, price

Yuichi S. Hayakawa

FIELD MEASUREMENT METHODFor acquisition of DEMs in field

Yuichi S. Hayakawa

Portable system for topographic measurement

• LRF with digital compass– Impulse 200 LR &

Mapstar by LaserTech• Portable DGNSS

– MobileMapper Pro by Thales Navigation

• Monopod with bipod legs

• Operating PC（早川・津村, 2008;

Hayakawa and Tsumura, 2009.）

Yuichi S. Hayakawa

Another combination

Trimble GeoXH 6000

LaserTechTruPulse 360B

Yuichi S. Hayakawa

Field measurement

Basepoint:DGNSS positioning

Laser measurements(distance, angles)

Yuichi S. Hayakawa

Measuring point:DGNSS positioning

Laser measurements(distance, angles)

Measurement by DGPS + LRF

(Base point:the first measuring point)

Yuichi S. Hayakawa

Data processing

Distance (horizontal)

Height (vertical)

Direct distanceElevation angleAzimuth(mag. north)

Raw Computed

Horizontal distanceHeightAzimuth(true north)

XYZ

(x, y, z) geographic coordinate by DGNSS

(BaseTarget)

Yuichi S. Hayakawa

Hacıtuğrul Tepe

Ankara

Study site

Turkey

SyiraIraq

Bulgaria Georgia

Greece

300 km

Yuichi S. Hayakawa

600 m !!

Hacıtuğrul Tepe

Yuichi S. Hayakawa

Base point coordinate32°13’16.9″E, 32°42’19.9″N, 915.8 m a.s.l.

Time for measurement 4 days for overall topography and 5 days for detailed local topographyBy 2 persons

Area and number of points approx. 1 km2

17,549 pts (13,217 pts after error reduction)11,017 pts (10,908 pts after error reduction)

Interpolation Method: Ordinary KrigingModel: Exponential for overall, Linear for localNugget effect: On Resolution (cell size): 4 m for overall, 0.2 m for local

Data property

Yuichi S. Hayakawa

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Sem

ivar

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Distance (m)

Actual dataSphericalCircularExponentialGaussianLinear with sill

Kriging interpolation (exponential)

4-m DEMSemivariogramPoint cloud

Overall topography

Yuichi S. Hayakawa

Topographic map of HacıtuğrulTepe

- 4 days by 2 operators- DEM resolution: 4 m- Contour interval: 0.5 m- Accuracy: ~1 m

300 m

Yuichi S. Hayakawa

927 m

890 m

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Actual dataSphericalCircularExponentialGaussianLinear with sill

Kriging interpolation (linear)

20-cm DEMSemivariogramPoint cloud

Partially high-resolution map

Point density is flexible.(trade-off with time)

Yuichi S. Hayakawa

0 60 12030 m

10-cm contour map and hillshade image

Yuichi S. Hayakawa

Interpolation

Point cloud DEM + Contour

Ras Jibsh, Oman

Kriging

Yuichi S. Hayakawa

Measurements of small tepes(~100 m)

Quick, accurate mapping

Zirayet Tepe Kale Höyük Dolma Tepe Hazarşah

Yuichi S. Hayakawa

Piz dal Büz(A) (B)

(C)

RTK-GPS mobile

DGPS base

RTK-GPS base

LRF

DGPS mobile

Operating PC

A rock glacier in Swiss Alps

Nr. Elevation (m) Difference (m) RTK-GPS Laser-DEM

01 2920.64 2919.88 -0.76 02 2841.43 2841.48 0.05 03 2840.07 2839.17 -0.90 04 2841.23 2841.71 0.48 05 2844.17 2843.99 -0.18 06 2854.75 2855.36 0.61 07 2853.74 2853.52 -0.22 08 2851.39 2851.70 0.31 09 2857.26 2857.42 0.16 10 2854.35 2854.16 -0.19 11 2864.24 2864.33 0.09 12 2865.56 2863.31 -2.25 13 2872.10 2873.22 1.12 14 2870.95 2871.60 0.65 15 2874.76 2875.90 1.14 　 　 Average: 0.01 　 Standard deviation: 0.83

Accuracy: 0.8 mcomparison with RTK-GNSS

Yuichi S. Hayakawa

Comparison with other DEMs

We can recently use various, worldwide topographic data, but their resolution is often low.

– How accurate or reliable? – Appropriate for what scale?

Here we compare several DEMs from different sources:

[ SRTM, GDEM, PRISM DEM, Field DEM ]

Yuichi S. Hayakawa

DEMs to compare• SRTM

– CGIAR-SCI (Filled GeoTIFF/ASCII), ver. 4– Resolution = 90 m

• GDEM– METI/NASA, ver. 1– Resolution = 30 m

cf. 2011/10/17 ver. 2 release• PRISM DEM

– AIST: GEOGrid PRISM DEM processing service– Resolution = 10 m

• Field DEM– LRF/DGNSS measurement– Resolution = 2 m

Yuichi S. Hayakawa

Study site

Yuichi S. Hayakawa

Eğriköy

• Early Bronze – Rome/Byzantine• Located at shoreline of old lake

(Sultansazligi)• 250 m long, 10 m high• Triangular shape (onigiri)

Yuichi S. Hayakawa

EğriköyField DEM >>> PRISM DEM >> SRTM > GDEM

SRTM(Contour=2m,10m)

GDEM(Contour=2m,10m)

PRISM DEM(Contour=2m,10m)

Field DEM(Contour=1m)

Yuichi S. Hayakawa

0

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1095 1100 1105 1110 1115 11200

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LRF

PRISM(10^2)

GDEM

SRTM(10^-1)

Elevation (m) Slope (degrees)

Curvature (m-1)

% %

%

Histograms

SRTMGDEMPRISM DEMField DEM

SRTM (10-1)GDEMPRISM DEM (102)Field DEM

Yuichi S. Hayakawa

ResultsApplicability

– 103 m scale objects: SRTM, GDEM, PRISM DEM, Field DEM

– 102 m scale objects: SRTM, GDEM, PRISM DEM, Field DEM

– 100–101 m scale objects: SRTM, GDEM, PRISM DEM, Field DEM

Advantages / Disadvantages– SRTM

• OK: Wide area / NG: Small (<102 m) objects– GDEM

• OK: Mountainous steep terrain / NG: Lowlands– PRISM DEM

• OK: Wide area, small objects (~102 m) / NG: Noisy– Field DEM

• OK: ~100 m very small objects / NG: Wide area (>100 km2)

Yuichi S. Hayakawa

Remarks• >102 m scale objects / >102 km2 extent

– SRTM• 102 m scale objects / 100–102 km2 extent

– PRISM DEM• 100–101 m scale objects / 10-1–100 km2 extent

– Field DEM

cf. Laser scanning technologies– ALS (Airborne laser scan)

• 100–101 m scale object / >100 km2 extent• Fine resolution, wide area

– TLS (Terrestrial laser scan)• 10-2–101 m scale object / 10-1–100 km2 extent• Very fine resolution, relatively narrow area

Select appropriate methods for appropriate scales/extent