PTT-102003 PTTSISTEM INFORMASI SUMBERDAYA LAHAN Kuliah ke 6
INPUT DATA GEOGRAFIK
PENDAHULUAN Input data geografik merupakan pekerjaan yang membutuhkan tenaga, waktu dan biaya yang cukup banyak (85 %) Minggu ini kita mempelajari sumber data dan cara input data. Sumber: primer dan sekender Cara: capture dan transfer
Data Input How do I transfer the paper map data and attribute data to a format that is usable by the GIS software? Data input involves both locational (map) and attribute data. The data can originate from various sources: – paper maps – attribute data on paper – other digital formats- databases (dBase), spreadsheets
(excel), or ASCII files
Sumber data Source Primary
Secondary
Raster Digital Satellite RS Image Digital aerial photographs Scanned maps or photographs Digital elevation models from topographic map contour
Vektor GPS Measurement Survey Measurement Topographic maps Toponymy (placename) database
Alur Input data Planning
Evaluation
Preparation
Editing/ Improvement
Digitizing/ Transfer
DATA PRIMER Data Raster: dari citra penginderaan jauh: AVHRR, Landsat, Aster, Spot, Ikonos, Quickbird, dll. – Dipilih sesuai dengan tujuan
Data Vektor: GPS – Ground survey membutuhkan waktu yang
cukup banyak.
DATA SEKUNDER Data Raster: Media analog cetakan di scan dengan resolusi sesuai kebutuhan (100 dpi, 200 dpi, 400 dpi, dst). – Untuk perencanaan detil perlu discan dengan
dpi tinggi.
Data Vektor: – – – –
Digitasi manual: menggunakan meja digitasi Heads-up digitizing and vectorization Kesalahan digitasi Fotogrametri.
Keyboard entry: (the source data only exists on paper)
mainly attribute data type data using keyboard data can be entered directly into a GIS table, spreadsheet, or database table.
Land survey: calculates coordinates on location (in the field) by measuring distances and angles, then entering the values into the software process uses coordinate geometry (COGO) process is used to draw legal documents ie. Parcel properties
Digitizing: A process that uses a device to extract spatial features from paper maps or photos to electronic GIS format Digitizing hardware: – table or tablet – grid of wires embedded in
surface • grid generates a magnetic field • that can be detected by a cursor
– cursor is a small flat device
contains a wire cross hair that
• cursor keypad allows special
Modes of Digitizing Two modes of digitizing: • point user identifies points to capture individually by pressing enter on cursor
• stream
points captured at set time intervals and/or movement of cursor
Point
Stream
Manual Digitizing ? The majority of spatial data entered into a GIS is from manual digitizing.
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Manual Digitizing The digitizing tablet and table allow information to be traced from an existing map or graphic. Three different types of tables or tablets exist. – (1) Acoustic – the digitizing pen emits a high
frequency sound that is received by microphones at the corners of the work area, triangulation is used to calculate the x and y coordinate of the pen. 4/1/2013
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GTCO CalComp Sonic Digitizer
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Types of Digitizers (Continued) (2) Resistivity uses two charged pads separated by a thin air gap, x and y coordinates are determined when the pads make contact. (3) The most widely used in large scale digitizers is the electronic digitizing tablet. Embedded below the surface of the table or the tablet is a grid of wires that measure the strength of the signal from the puck or the pen 4/1/2013
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Qualities of a Digitizer – Stability
• The ability of the digitizer to maintain a value as the puck remains in one place. – Repeatability • Precision • Good digitizers accurate to 0.001 inch
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Qualities of a Digitizer #2 – Linearity
• the ability to be within a specified distance of the correct value • Good digitizers are able to have a linearity of 0.003 inch over 60 inches – Skew • The ability to produce coordinates in a true rectangle. 4/1/2013
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Digitizing Procedures The Map is fixed to the digitizing table. Three or more control points are digitized. – Easily identified points (intersections of major streets,
major peaks, points on coastline) – These coordinates will be known or verified – The digitizing area is registered to the map area.
Digitizing the map can be done in two ways. – In point mode , the operator identifies the points
captured explicitly by pressing a button. – In stream mode the points are captured at regular intervals (time or distance) 4/1/2013
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Digitizing Procedures (cont) Point mode is done subjectively by the operator (no two operators will digitize the same). Stream mode generates a large number of points, many of which will be redundant. Most digitizing is done in point mode.
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Advantages of Digitizing Low initial capital cost Flexible and adapts to different types of data Easily mastered skill Digitizing devices are reliable Generally the quality of data is high 4/1/2013
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Digitizing Vendors Altek Calcomp Didger GTCO Kurta
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Problems Problems or Errors using Digitizing: - Paper maps can stretch/ shrink. Lose accuracy. - Paper maps meant to display information, not record locational (x,y) information. - Discrepancies across map sheets to digitize. (ie roads do not match when 2 maps digitized.) - User error such as overshoots, undershoots, or spikes
Overshoot
Undershoot
Spike
Problems To avoid or correct overshoots, undershoots, or spikes: • use clean function •“snap” to nodes
Before
After
overshoot
Dangling segmen
undershoot
Sliver polygon
Scanning Technology Converts paper maps into digital format by capturing features as cells, or pixels. Cells are captured using a scanner head made up of photosensitive cells. Advanced large format scanners have heads with 8000 photosensitive cells Each sensor is able to record a pixel rated between 0 (black) to 255 (white) and any graytones between. 4/1/2013
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Color Scanning Technology Color images use the same technique but the image is scanned for red, blue and green. Older scanners required the image being scanned to pass the scanning head in three passes. Vectorization often requires color scanning 4/1/2013
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Color Scanning Technology Filters allow the head to pass the image once scanning all three colors at once The latest technology: full width, single line, sensor array scanning uses a line of LED’s which capture the image LED scanners can create images using 16.8 million colors at speeds several times faster than previously obtained. 4/1/2013
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Scanning Problems Higher resolutions aren’t always the answer to better data; often the additional “noise” and resulting clean up of data can cause higher resolution to not be the best solution, a balance between detail and additional manual clean-up must be struck. Paper maps are not “dimensionally stable” and a great deal of variation occurs as the maps age. Documents must be clean (no smudges or extra marks or lines). 4/1/2013
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Scanning Problems #2 Text may accidentally be scanned as line features in automatic feature recognition. Specialized symbols (for example marsh or asphalt) may not be detected as such.
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IDEAL Large Format Monochrome Scanners Model
Price
FSS 4300DSP FSS 8300DSP FSS 12300DSP
$6,675 $10,425 $11,925
max dpi
Paper Size 200 800
1200
Speed
36 in.
15 sec.
36 in.
17 sec.@200 dpi
36 in.
25 sec.@200 dpi
FSS 18300DSP
$13,425
1800
36 in.
34 sec.@200 dpi
Super Wide 2250
$13,425
400
50 in.
3 in./sec.
Super Wide 2251
$14,925
800
50 in.
6 in./sec
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Model
Price
max dpi
Paper Size
Speed
ANAtech Binary & Grayscale Scanners 400 36 in.
3"/sec @ 200 dpi
800 36 in.
3"/sec @ 200 dpi
$12,500
800 36 in.
6.4"/sec @ 200 dpi
1270 Digidot
$50,000
1270 27 in.
Unknown
Eagle 4225
$55,000
2540 42 in.
Unknown
Evolution 4 Evolution 8 Evolution Pro
$10,000 $11,000
High Resolution Monochrome Scanners
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Price Model
Paper max dpi Size
Speed
Large Format Color Scanners ESC 5010 DSP FSC 8010 DSP
$11,175 $14,925
500 800
36 in.
36 sec.@200 dpi
36 in.
48 sec.@200 dpi
Large Format Color Scanners Colortrac 5480 Eagle 6250C 4/1/2013
$31,000
800 54 in.
$142,000
1000 62 in.
1.5"/sec. @ 200dpi Unknown 32
Vendors for Scanners Widecom Scanners – www.widecom.com/
Anatech Scanners – www.anatech.com/
Vidar Systems Corporation – www.delinfotek.com/
Abakos Digital Images – www.abakos.com.au/
Contex Scanning Technologies – www.caddcentreindia.com/ 4/1/2013
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Digitizer or Scanner Scanners – Speed and ease – Raster data without intelligence; manual or automatic vectorisation possible. – Usually produces large files that need compression – Hardware is expensive
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Digitizers – Labor intensive – Requires skilled operator – Vector (intelligent) data – Labor intensive – Hardware less expensive
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Scanning & Digitizing Input Errors Incompleteness of the spatial data; missing points, line segments, and polygons. Location placement errors of spatial data; careless digitizing or poor quality of the original source. Distortion of spatial data; base maps that aren’t scale correct over the entire image or from material stretch in paper maps. 4/1/2013
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Scanning & Digitizing Input Errors #2 Incorrect linkage between spatial and attribute data; misplaced labels or unique identifiers being assigned during manual key entry or during the initial setup. Attribute data is wrong or incomplete; missing data records or data records from different time periods. Redundant information, including vertices, text, nodes, and arcs. Incorrect label information and placement. 4/1/2013
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Common Spatial Errors Slivers or gaps in the line work. Dead ends, dangling arcs, overshoots and undershoots. Bow ties or weird polygons caused by inappropriate closings of connecting features.
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Data Verification Visual review; usually done by reviewing a check plot (hard copy). Cleanup of lines and junctions; this process is usually done by software and then through manual editing. Check source maps, if additional copies of the same map are available compare them to see if stretching of the map has occurred. Check output drawing to see if text or symbols were read as features if software is used to convert the drawings. 4/1/2013
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DATA TRANSFER Dari format data lain
Data Yang Dimasukkan DATA ANALOG – Peta – Data Tabulasi DATA DIGITAL – Peta – Tabel • Disesuaikan dengan tujuan dan data yang tersedia • Menentukan keefisienan dan keefektifan sistem pengelolaan data dalam SIG • Berpengaruh terhadap besarnya data yang diperlukan
PERSIAPAN PEMASUKAN DATA TERGANTUNG DARI DATA YANG TERSEDIA Data tabular: diketik ke dalam “spread sheet” Foto Udara: – Interpretasi – Koreksi geografik – Digitasi
Data dijital lain – Konversi ke format yang dituju
Data lapangan: – Tabulasi – Klasifikasi
PERSIAPAN PEMASUKAN DATA Pertimbangan lain: a. Kualitas data sering dipengaruhi oleh lembaga penghasil data Lokal: – hanya untuk kepentingan sendiri sulit diintegrasi
Regional/Nasional: – untuk kepentingan banyak pemakai mudah diintegrasi
b. Sumber data •
lapangan
•
interpretasi citra (foto udara/satelit)
PERSIAPAN PEMASUKAN DATA Pertimbangan lain: c. Waktu pengambilan tergantung macam data: data vegetasi/penggunaan lahan sebaiknya yang terbaru tanah: bisa lama asal klasifikasinya sama untuk monitoring: periode waktu tertentu tergantung tujuan, harian, mingguan, bulanan, tahunan, dll d. Lain-lain
SUMBER & ALAT PEMASUKAN DATA SPASIAL SUMBER DATA
ALAT PEMASUKAN
Peta Analog, Foto Udara, dll
Meja digitasi Scanner digitasi di layar
Data tabel
Keyboard
Data dijital
Konversi ke format yang dituju Floppy disk CD Dll
Koordinat Lapangan Dll ….
GPS Dll …..
Editing Dilakukan bila ada kesalahan dalam pendigitasian dengan menggunakan meja digitasi
1. Berkaitan dengan kondisi geometrik a. Node hilang/bergeser b. Ujung hilang/bergeser
2. Berkaitan dengan topologi: a. b. c. d. e. f.
Ujung tidak berkaitan Ada antara/gap Garis ganda Garis lebih Poligon aneh dll
Pemasukan dengan Scanner Produknya berupa data raster Perlu perampingan bentuk garis agar koordinatnya dapat dikenali dengan baik Kadang perlu vektorisasi Untuk data yang kompleks (misal peta topografi), seringkali harus dilakukan penggambaran kembali Ada dua macam: – flat-bed scanner – drum-scanner
Pemasukan dengan Digitasi Layar Komputer Peta disiam (dengan menggunakan scanner) Ditampilkan pada layar monitor Didigitasi langsung di layar (+ editing jika terjadi kesalahan) Registrasi untuk mendapatkan koordinat Bermanfaat untuk menambah informasi yang tidak terdapat pada peta asli, misal pola drainase yang wilayah berbukit/bergunung. Dengan melakukan overlay dengan foto udara atau citra satelit pola drainase dapat ditambahkan.
Pemasukan data dengan GPS Untuk koreksi geometri Menentukan koordinat obyek di lapangan secara tepat, misal lokasi pemboran, minipit, profil tanah dsb. Bisa berfungsi sebagai digitasi obyek di lapangan Kelemahan: membutuhkan ruang terbuka, pada ruang yang tertutup (dibawah pohon) menghasilkan deviasi yang besar
Digitasi konvensional vs GPS KONVENSIONAL
GPS
Ketelitian bergantung skala
Ketelitian tidak bergantung skala
Cocok untuk koleksi data yang besar
Cocok untuk koleksi data yang selektif
Kecepatan pendigitasian dikontrol oleh pengguna
Kecepatan pendigitasian dikontrol oleh batas kecepatan dan kondisi lalu lintas
Cocok untuk obyek-2 yang dapat terlihat pada peta atau foto udara
Dapat juga digunakan untuk obyek-2 kecil
Digitizer 2 dimensi
Digitizer 3 dimensi
Pendigitasian point-mode
Pendigitasian dengan metode penentukan posisi statik singkat, stop and go atau pseudo-kinematik
Pendigitasian stream-mode
Pendigitasian dengan metode penentukan posisi kinematik GPS
Operator lapangan harus terlatih
Staff biasa dapat melakukan pengukuran
Perlu ada “land mark” lapang
Perlu ada “land mark” lapang
Data non digital
Data digital
PEMANFAAT DATA DIGITAL Dinegera maju data digital dan pendukungnya sudah banyak tersedia Di Indonesia sedang dirintis Lembaga yang mengurusi: BAKOSURTANAL (Badan Koordinasi Survei dan Pemetaan Nasional) Format data spasial yang ada: ArcInfo, ArcView, Erdas, Idrisi, ILWIS, Auto-cad, MapInfo, kadang juga dalam bentuk BMP, TIFF, JPG.
DATA YANG TERSEDIA Data kartografik: – Bakosurtanal
Data sumberdaya alam – Tanah: Puslitbangtanak, Bogor – Penggunaan Lahan: BPN – Geologi: Puslitbang Geologi Bandung
Data elevasi digital Data kartografik berkaitan dengan sensus – BPS
