oleh : Dr. Taufik Hery Purwanto, M.Si.
• Titik • Garis • Polygon
3D/Surface Analysis
Network Analysis
Image Processing
Address Locator/ Geocoding
Modeling Our World, Michael Zeiler, 1999
Pulau Bali dalam tampilan 3-Dimensi
Mount Saint Helens
Apa itu D E M ?
Great 3D model of a cave that combines laser point cloud data with high-res photos
Different types of geographic phenomena
Fields
Continuous Temperature
Objects
Discrete Landuse
Buildings
Continuous fields – Discrete fields
Landuse
Elevation
http://gisgeography.com/inverse-distance-weighted-idw-interpolation/
Topographic Maps
2. Pengertian Digital Elevation Model (DEM) • DEM adalah data digital yang menggambarkan geometri dari bentuk permukaan bumi atau bagiannya yang terdiri dari himpunan titik-titik koordinat hasil sampling dari permukaan dengan algoritma yang mendefinisikan permukaan tersebut menggunakan himpunan koordinat (Tempfli, 1991).
Z = f(x,y) dimana : x,y = posisi Z = nilai ketinggian
Relief medan dan model digital (Temfli, 1991)
2. Pengertian Digital Elevation Model (DEM)
lanjutan
• DEM merupakan suatu sistem, model, metode, dan alat dalam mengumpulkan, prosessing, dan penyajian informasi medan. Susunan nilai-nilai digital yang mewakili distribusi spasial dari karakteristik medan, distribusi spasial di wakili oleh nilai-nilai pada sistem koordinat horisontal X Y dan karakteristik medan diwakili oleh ketinggian medan dalam sistem koordinat Z (Frederic J. Doyle, 1991)
• DEM khususnya digunakan untuk menggambarkan relief medan. Gambaran model relief rupabumi tiga dimensi (3-Dimensi) yang menyerupai keadaan sebenarnya di dunia nyata (real world) divisualisaikan dengan bantuan teknologi komputer grafis dan teknologi virtual reality (Mogal, 1993) • A digital elevation model is a digital model or 3D representation of a terrain's surface (wikipedia.org)
Beda Pengertian DEM dan DTM • • • • • •
DEM (Digital Elevation Model) was widely used in America DTM (Digital Terrain Model), DHM ( Digital Height Model) came fromGermany DGM ( Digital Ground Model) was used in the United Kingdom DSM (Digital Surface Model) DTEM (Digital Terrain Elevation Models) was introduced and used by USGS and DMA (DefenseMapping Agency) I. Sejarah (yang mempopulerkan) : DEM : USGS (United State Geological Survey) berstruktur data grid DTM : The Defence Mapping Agency berstruktur data garis (arc) dengan TIN (Triangular Irregular Network). II. Menyangkut pengertian informasi : elevasi elevasi + informasi morfologi elevasi + layer permukaan
DEM DTM
If we use the term digital elevation model (DEM) to refer to terrain models with elevation information only, while the term digital terrain model (DTM) refers to a much broader concept of terrain representation, including terrain parameters such as slope and aspect, terrain features such as ridges and valleys and other geographical/environmental characteristics, DTA specifies the process that transforms DEMs to DTMs, using the principles and knowledge of geography, or other application fields. (Hutchinson and Gallant 1999).
1. Ground: “the solid surface of the earth”; “a solid base or foundation”; “a surface of the earth”; “bottom of the sea”; etc. 2. Height: “measurement from base to top”; “elevation above the ground or recognized level, especially that of the sea”; “distance upwards”; etc. 3. Elevation: “height above a given level, especially that of sea”; “height above the horizon”; etc. 4. Terrain: “tract of country considered with regarded to its natural features, etc.”; “an extent of ground, region, territory”; etc. Li (1990)
DSM dan DTM ORI
Orthorectified
DEMs
Digital Surface Model
Digital Terrain Model
Digital Surface Models (DSM) Elevation model that displays the elevation of the first surface on the ground. Digital Terrain Models (DTM) DSMs are used to create DTMs by digitally removing all cultural features and treed areas. DTMs are useful for applications where an accurate sense of the underlying terrain is required.
DSM dan DTM • •
DSM - Elevation of the first surface the radar comes in contact with. DTM - Derived from the DSM: elevations values approaching bare earth.
DSM and DTM: Shaded-Relief Example
DSM
DTM
Digital Surface Model
Digital Terrain Model
DSM and DTM: Shaded-Relief Example
Tip: To see the difference between the DSM and the DTM, toggle back and forth between images.
3. Data DEM 3.1. Sumber Data DEM • FU stereo - Photogrammetric techiques • Citra satelit stereo - Stereo-pairs technique • Data pengukuran lapangan : GPS, Theodolith, EDM, Total Station, Echosounder - Interpolation technique • Peta topografi - Interpolation technique • Radar - Radar technique • Lidar - Laser scanner technique
3.2. Bentuk Data DEM • Titik (titik tinggi) • Garis (kontur) • Penyiaman (LIDAR)
-From terrestrial measurements with precise land survey instruments These spot measurements are then interpolated into an elevation surface. With this method, it is costly and time-consuming to cover bigger areas.
- From airborne or satellite remote sensing
Stereo is images, or LIDARgenerated? data are used in a semi-automated process to create a DEM. How aRADAR DEM
RADAR Interferometry with 2 receivers, 60m apart
Airborne Laserscanning or LIDAR
Model turunan geometri foto udara untuk penjabaran perbedaan tinggi
System Airbone LiDAR terdiri dari: 1. Laser sensor 2. Camera sensor 3. GPS receiver 4. Inertial Measurement Unit (IMU) 5. Komputer dan Storage data (tempat penyimpanan data).
• Digital terrain model generation – airborne laser scanning • Laser pulse is emitted from the sensor – return journey time is measured, giving distance between sensor and target • Location of the sensor is determined by GPS • Therefore target can be located • Significant post processing is required: – Data thinning – Gridding
Horizontal resolution: 2m Vertical accuracy: ± 2cm
http://sujanayogi.wordpress.com/2010/02/01/3d-laser-scanner/
pointcloud
http://sujanayogi.wordpress.com/2010/02/01/3d-laser-scanner/
pointcloud
http://sujanayogi.wordpress.com/2010/02/01/3d-laser-scanner/
* Based on the accuracy of the accompanying ORI
** Relative to Fligth Altitude
Map Scales and Commonly Used Contour Intervals (Konecny et al. 1979)
In general, it is expected that the height accuracy of any point interpolated from contour lines will be about 1/2 to 1/3 of the CI.
Map Scales and Commonly Used Contour Intervals
α is the slope angle
Three new global topographic datasets available (SRTM Ellipsoidal, ALOS World 3D, GMRT) 1. SRTM GL1 (30m Ellipsoidal) is a version of the popular Shuttle Radar Topography Mission dataset where elevation values are WGS84 ellipsoidal height as opposed to the standard orthometric, or geoid-referenced, elevation. OpenTopography constructed this dataset by subtracting the EGM96 geoid model from the standard SRTM GL1 data. This dataset was produced primarily to support the InSAR community and their need for ellipsoidal referenced DEMs for terrain correction, although we suspect other users may find the dataset valuable.
2. ALOS World 3D - 30m is a freely available, downsampled version of a high-resolution (5m) dataset collected by The Japan Aerospace Exploration Agency (JAXA). The ALOS World 3D - 30m dataset is a digital surface model derived from satellite-based stereo-photogrammetry. ALOS World 3D provides data coverage up to 82° latitude (up to 84° in parts of Greenland). This includes a vast part of Antarctica not covered by SRTM. Data quality has also been described as comparable or superior to SRTM [1] [2]. Another important distinction between the two is that the version of SRTM provided by OpenTopography has most void spaces filled with data from other sources, while ALOS World 3D has not been void-filled, thus SRTM will likely remain the preferred data source for many areas and applications.
http://www.opentopography.org/news/three-new-globaltopographic-datasets-available-srtm-ellipsoidal-alos-world-3d-gmrt
SRTM GL1 (30m Ellipsoidal)
ALOS World 3D datasets over Oahu, Hawaii. Areas shown in green are no data void spaces.
http://www.opentopography.org/news/three-new-globaltopographic-datasets-available-srtm-ellipsoidal-alos-world-3d-gmrt
3. the Global Multi-Resolution Topography (GMRT) Our third new dataset, the Global Multi-Resolution Topography (GMRT) Data Synthesis is a bathymetric dataset derived from a collection of multibeam sonar data. The GMRT dataset represents a new and unique workflow on OpenTopography. Data is accessed seamlessly on the OpenTopography site from an external web service. Although the data are sourced from an external service call, users can still perform the typical OpenTopography processing available for rasters, such as creating colorrelief and hillshade images, on the selected data.
SRTM GL1 (30m Ellipsoidal)
GMRT datasets over Oahu, Hawaii. GMRT is lower resolution onshore, but shows considerable bathymetric detail offshore.
There is a variety of DEM source data available for developed areas and the suitability of this available data is depending on the project specifications. In remote regions around the World, were little or no source data is available, the DEM can be produced by automatic DEM extraction from stereo satellite imagery, from satellite sensors such GeoEye-1, WorldView-1, WorldView2, IKONOS, Pleiades-1, SPOT-5, SPOT-6 and SPOT-7 satellite sensors. The Pleiades-1A and Pleiades-1B Satellite sensors can be programmed to collect Tri-Stereo Imagery for the production of high quality 1m-2m DEM's for 3D Urban and Terrain modeling. The Tri-Stereo acquisitions reveal elevation that would otherwise remain hidden in steep terrain or urban canyons in dense built-up areas.
http://www.satimagingcorp.com/services/dem/
http://gisgeography.com/free-global-dem-data-sources/
Last updated: Monday, February 27, 2017
1 1. Space Shuttle Radar Topography Mission (SRTM) NASA only needed 11 to obtain their impeccable SRTM 30-meter digital elevation model of the Earth. The SRTM payload was equipped on the Space Shuttle Endeavour back in February 2000. Using two radar antennas and a single pass, it collected sufficient data to generate a digital elevation model using a technique known as interferometric synthetic aperture radar (inSAR). C-Band penetrated canopy cover to the ground better but SRTM still struggled in sloping regions with foreshortening, layover and shadow. In late 2014, the highest possible resolution SRTM data was released to the public. This 1-arc second global digital elevation model has a spatial resolution of about 30 meters covering most of the world with absolute vertical height accuracy of less than 16m. Where can you download the SRTM data? SRTM DEM data is being housed on the USGS Earth Explorer. To download, select your area of interest. Under the data sets tab, select Digital Elevation > SRTM > SRTM 1-ArcSecond Global . But here’s a USGS Earth Explorer download guide to help you get started.
2. ASTER Global Digital Elevation Model A joint operation between NASA and Japan was the birth of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). As part of this project emerged the ASTER Global DEM. ASTER GDEM boasted a global resolution of 90 meters with a resolution of 30 meters in the United States. Despite its high spatial resolution and greater coverage (80% of the Earth), users were dissatisfied with it because of its artifacts, which often occurred in cloudy areas. ASTER used stereoscopic pairs and digital image correlation methods. Two (passive) optical images were acquired with different angles taken from the same pass of an airplane. These visible and nearinfrared bands of ASTER were affected by cloud cover. This wasn’t the case for SRTM’s C-Band radar. Here’s how passive and active sensors are different.
However over time, ASTER DEM data has improved its products with artifact corrections of their own. During October 2011 ASTER version 2 of Global Digital Elevation Model was publicly released, which considerably improved on version 1. Despite being experimental grade, ASTER version 2 can be considered a more accurate representation than the SRTM elevation model in rugged mountainous terrain. But you should really take a look for yourself. Where can you download the ASTER GDEM? You can download the ASTER DEM data for free from the USGS Earth Explorer. Under the data sets tab, select Digital Elevation > ASTER .
3 3. JAXA’s Global ALOS 3D World The ALOS World 3d is a 30-meter spatial resolution digital surface model (DSM) constructed by the Japan Aerospace Exploration Agency’s (JAXA). Recently, this DSM has been made available to the public. The neat thing about is that it is the most precise global-scale elevation data at this time using the Advanced Land Observing Satellite “DAICHI” (ALOS). The DSM was generated using stereo mapping (PRISM) for worldwide topographic data with its optical stereoscopic observation. Where can you download the JAXA’s Global ALOS 3D World? In order to obtain this highly accurate DSM, you’ll have to register online through the JAXA Global ALOS portal to download it.
4. Light Detection and Ranging (LiDAR) You might think that finding LiDAR is a shot in the dark. But it’s not anymore. Slowly and steadily, we are moving towards a global LiDAR map. With Open Topography topping the list at #1, we’ve put together a list of some of the 6 best LiDAR data sources available online for free. Because nothing beats LiDAR really in terms of coverage and accuracy. Filtering ground returns, you can build an impressive DEM from LiDAR. …And if you still can’t find anything in the link above, try your local or regional government. If you tell them what you are using it for, they sometimes hand out LiDAR for free.
5. Mars Orbiter Laser Altimeter (MOLA) Just throwing this out here to peak your interest. Earth isn’t the only surface being mapped for elevation. You can go for a spin on the rugged terrain of Mars using data captured by the Mars Orbiter Laser Altimeter (MOLA) instrument as shown in the Mars Terrain map. In fact, the data captured from the MOLA instrument data was used to map out ancient streams on Mars. If this doesn’t excite you, I don’t know what would.
Where can you download the MOLA DEM of Mars? The USGS Astrogeology Science Center is the DEM data hub for Mars. Elevations above the areoid were determined from a Martian gravity field solution GMM-2B with a total elevation uncertainty of at least ±3m.
3. Data DEM 3.3. Struktur Data DEM
Grid
TIN
Countour
DEMs and TINs
DEM with sample points
TIN based on same sample points
Grid Surface Data Model Raster-based digital elevation model – Regular spaced set of elevation points (z-values) a sampled array of elevations (z) that are at regularly spaced intervals in the x and y directions. two approaches for determining the surface z value of a location between sample points. • In a lattice, each mesh point represents a value on the surface only at the center of the grid cell. The z-value is approximated by interpolation between adjacent sample points; it does not imply an area of constant value. • A surface grid considers each sample as a square cell with a constant surface value.
Raster representation of a surface
Grid atau Lattice Grid atau Lattice menggunakan sebuah bidang segitiga teratur, segiempat, atau bujursangkar atau bentuk siku yang teratur grid. Perbedaan resolusi grid dapat digunakan, pemilihannya biasanya berhubungan dengan ukuran daerah penelitian dan kemampuan fasilitas komputer. Data dapat disimpan dengan berbagai cara, biasanya metode yang digunakan adalah koordinat Z berhubungan dengan rangkaian titik-titik sepanjang profil dengan titik awal dan spasi grid tertentu (Moore et al., 1991).
Lattice
dan
Grid
Advantages and Disadvantages of Grid Surface Data Model Advantages: • Simple conceptual model • Data cheap to obtain • Easy to relate to other raster data • Irregularly spaced set of points can be converted to regular spacing by interpolation Disadvantages: • Does not conform to variability of the terrain
• Linear features not well represented
Thana Chirapiwat, Faculty of Architecture, Silpakorn University (2015)
Grid Surface Data Model
Grid Surface Model:
• • • • • •
Raster data model using a mesh of regularly spaced points Simple and easy to process, take a lot of storage space ‹Fixed-resolution determined by the cell size as a result of interpolation Rigid mesh structure does not adapt to the variability of terrain Source data may not be captured, which may cause lose of information ‹Prevent linear features from being represented sufficiently Dr. Fang Qiu
•
A triangulated irregular network (TIN) is a data model that is used to represent three dimensional objects. In this case, x,y, and z values represent points. Using methods of computational geometry, the points are connected into what is called a triangulation, forming a network of triangles. The lines of the triangles are called edges, and the interior area is called a face, or facet.
•
The illustration shows how we can create a TIN of the terrain around Ithaca, NY. – First, a series of elevation points are created – Second, a TIN face is created with the elevation data – Third, the faces are shaded in to give the impression of a 3D surface
©Arthur J. Lembo Cornell University
From these input points, a triangulation is performed on the set of points. In a TIN, the triangles are called faces, the points become nodes to a face, and the lines of faces are called edges.
TIN Surface Data Model
TIN: ‹ ector data model using continuous, nonoverlappingtriangle facets. V ‹Elevation values (z) along with x, y coordinates are stored as node of the triangles ‹Take less storage space but difficult to process ‹Variable-resolution adapt to the variability of terrain and perform resolution adapt to the variability of terrain and perform interpolation on the fly • ‹More detailed when surface is complex, less detailed when simple • ‹Source data maintained as part of triangulation, no information lose • ‹Can represent linear features by enforcing them as triangle edges (breakline) • • • •
Dr. Fang Qiu
Advantages and Disadvantages of TIN Advantages • Can capture significant slope features (ridges, etc) • Efficient since require few triangles in flat areas • Easy for certain analyses: slope, aspect, volume Disadvantages • Analysis involving comparison with other layers difficult
Thana Chirapiwat, Faculty of Architecture, Silpakorn University (2015)
Contour Vector-based contour lines – Lines joining points of equal elevation, at a specified interval
Kontur Kontur dibuat dari digitasi garis kontur yang disimpan dalam format seperti DLGs (Digital Line Graphs) dengan membuat sepasang koordinat (x, y) sepanjang tiap garis kontur yang menunjukkan elevasi khusus. Kontur paling banyak digunakan untuk menyajikan permukaan bumi dengan simbol garis.
Advantages and Disadvantages of Contour Advantages: • Familiar to many people • Easy to obtain mental picture of surface o Close lines = steep slope o Uphill V = stream o Downhill V or bulge = ridge o Circle = hill top or basin
Disadvantages: • Poor for computer representation: no formal digital model • Must convert to raster or TIN for analysis • Contour generation from point data requires sophisticated interpolation routines, often with specialized software such as Surfer from Golden Software, Inc., or ArcGIS Spatial Analyst extension
Thana Chirapiwat, Faculty of Architecture, Silpakorn University (2015)
3. Data DEM 3.4. Sampling Data DEM
III
(Tempfli, 1991)
3. Interpolasi Interpolasi adalah proses penentuan dari nilai pendekatan dari variabel f(P) pada titik antara P, bila f(P) merupakan variabel yang mungkin skalar atau vektor yang dibentuk oleh harga f(P1) pada suatu titik P1 dalam ruang yang berdimensi r (Tempfli, 1977).
Penentuan nilai suatu besaran berdasarkan besaran lain yang sudah diketahui nilainya, dimana letak dari besaran yang akan ditentukan tersebut di antara besaran yang sudah diketahui. Besaran yang sudah diketahui tersebut disebut sebagai acuan, sedangkan besaran yang ditentukan disebut sebagi besaran antara (intermediate value). Dalam interpolasi hubungan antara titik-titik acuan tersebut didekati dengan menggunakan fungsi yang disebut fungsi interpolasi.
Interpolasi spasial suatu proses mengidentifikasi nilai Z pada lokasi yang baru berdasarkan karakteristik poin kontrol yang telah ditentukan (Jensen, 2013)
Interpolasi spasial 1. Global Interpolation merupakan metode yang menggunakan dasar setiap nilai point yang ada dapat digunakan untuk mengestimasi nilai baru. Secara konseptual global interpolation didisain untuk mendapatkan trend suatu nilai. Contoh: trend surface dan regression 2. Local Interpolation mengestimasi suatu nilai baru hanya menggunakan beberapa nilai point yang dijadikan sebagai sampel. Contoh: thiessen, density estimation, inverse distance weighted, splines, dan kriging. (Chang, 2012)
Interpolasi menentukan titik-titik antara n buah titik Interpolasi 1. Interpolasi Linier 2. lnterpolasi Kuadratik 3. lnterpolasi Polinomial
Z = f(X, Y)
Surface shapes of the first 4 terms of general polynomial function.
menentukan titik-titik antara 2 buah titik dengan menggunakan pendekatan fungsi garis lurus
Persamaan garis lurus yang melalui 2 titik P1(x1,y1) dan P2(x2,y2) Sehingga diperoleh persamaan dari interpolasi linier :
Algoritma Interpolasi Linier : 1. Tentukan 2 titik P1, dan P2 dengan koordinatnya masing-masing (x1,y1) dan (x2,y2). 2. Tentukan titik x dari titik yang akan dicari 3. Hitung nilai y dengan :
4. Tampilkan nilai titik yang terbaru
menentukan titik-titik antara 3 buah titik dengan menggunakan pendekatan fungsi kuadrat
3 titik yang diketahui: P1(x1,y1), P2(x2,y2) dan P3(x3,y3)
Untuk memperoleh titik Q(x,y) digunakan interpolasi kuadratik :
Algoritma Interpolasi Kuadratik : 1. Tentukan 3 titik P1, P2 dan P3 dengan koordinatnya masing-masing P1(x1,y1), P2(x2,y2) dan P3(x3,y3)
2. Tentukan titik x dari titik yang akan dicari 3. Hitung nilai y dengan :
4. Tampilkan nilai titik yang terbaru
Contoh penyelesaian Interpolasi Kuadratik
Cari nilai y untuk titik x=2.5 yang berada di antara titik (1,5), (2,2) dan (3,3) Jawab: P1(1,5) , P2(2,2) dan P3(3,3) x=2.5
Titik baru: P4(2.5,2)
menentukan titik-titik antara N buah titik dengan menggunakan pendekatan fungsi polynomial pangkat N-1 Titik-titik yang diketahui: P1(x1,y1), P2(x2,y2), P3(x3,y3) … PN(xN,yN)
Persamaan polynomial pangkat N-1
Masukkan nilai dari setiap titik ke dalam persamaan polynomial di atas, diperoleh persamaan simultan dengan n persamaan dan n variabel bebas
Contoh Interpolasi linier
Aronof (1993) mengungkapkan perbedaan metode interpolasi akan menghasilkan DEM yang berbeda.
Boltstad (2012) juga mengemukakan pendapat yang sama bahwa walaupun menggunakan input data yang sama dengan metode interpolasi yang berbeda maka DEM yang dihasilkan akan berbeda. Li dan Heap (2008) menjelaskan ada 42 metode interpolasi yang dikategorikan menjadi interpolasi geostatistik, non-geostatistik dan gabungan Perbedaan DEM yang dihasilkan tersebut akan mempengaruhi kualitas dari sebuah DEM.
•
Pengukuran Jarak, posisi (surface length, Surface Point, Surface volume)
•
Volume
•
Cut/fill
•
Penentuan Jarak dan Arah (Geodesy Graphic Tools)
•
Titik Tertinggi dari suatu lokasi (Find Highest Point)
•
Titik Terendah dari suatu lokasi (Find Lowest Point)
•
Line of Sight (LOS)
•
Profil
•
Peta Kelas Elevasi
•
Peta Kontur dengan berbagai CI
•
Model tiga dimensional (pandangan perspektif medan atau pandangan mata burung/bird's eye view)
•
Peta tematik dalam bentuk tiga dimensional
•
Peta lereng (Slope)
•
Peta aspek (Aspect)
•
Efek bayangan (hill shading)
•
3-D “real time” atau “Fly by Animation”
5. Turunan DEM
lanjutan
Tampilan Perspektif 3 Dimensi - (bird’s eye view) Tampilan 3-D juga dapat menghasilkan penyajian permukaan dan informasi terrain. Pada bird’s eye view, azimuth dan attitude (tinggi) pengamat yang berkaitan dengan permukaan dapat ditentukan. Pada gambar 3-D di permukaan, lokasi pengamat dan titik target biasanya ditentukan. Drape permukaan membuat tampilan 3-Dimensi layer lain yang memiliki koordinat yang sama dengan TIN. Drape mengenakan titik dan garis.
5. Turunan DEM
lanjutan
Kontur Kontur (isoline) adalah garis yang 5121000 menggambarkan satu elevasi konstan pada suatu permukaan. Biasanya 5120000 kontur digunakan untuk 5119000 memvisualisasikan elevasi pada peta 2-Dimensi. 5118000
5117000
5116000
5115000
5114000
5113000
5112000
5111000
5110000
5109000
558000 559000 560000 561000 562000 563000 564000 565000 566000 567000
5. Turunan DEM
lanjutan
Kontur
The creation of isopleth maps: (A) point attribute values; (B) user-defined classes; (C) interpolation of class boundary between points; (D) addition and labeling of other class boundaries; and (E) use of hue to enhance perception of trends (after Kraak and Ormeling 1996: 161
5. Turunan DEM
lanjutan
Profil Profil adalah irisan penampang 2-Dimensi dari suatu permukaan. Berdasarkan profil dapat dipergunakaan untuk analisa morfologi permukaan seperti : kecekungan permukaan, perubahan permukaan, kecembungan permukaan, dan ketinggian maksimum permukaan lokal.
5. Turunan DEM Profil
lanjutan
Garis penglihatan (line of sight) Garis antara 2 titik yang menunjukkan bagian-bagian dari permukaan sepanjang garis yang tampak (visible) atau tidak tampak (hidden) dari pengamat.
5. Turunan DEM Efek bayangan (hillshading) Efek bayangan suatu permukaan berdasarkan harga reflektansi dari features permukaan sekitarnya, sehingga merupakan suatu metode yang sangat berguna untuk mempertajam visualisasi suatu permukaan. Efek bayangan dihasilkan dari intensitas yang berkaitan dengan sumber cahaya yang diberikan. Sumber pencahayaan yang dianggap pada jarak tak berhingga daripada permukaan, dapat diposisikan pada azimuth dan altitude (ketinggian) yang telah ditentukan relatif terhadap permukaan.
lanjutan
Kemiringan lereng (slope) Kemiringan lereng adalah suatu permukaan yang mengacu pada perubahan harga-harga z yang melewati suatu daerah permukaan. Dua metode yang paling umum untuk menyatakan kemiringan lereng adalah dengan pengukuran sudut dalam derajat atau dengan persentase. Contohnya, kenaikan 2 meter pada jarak 100 meter dapat dinyatakan sebagai kemiringan 1,15 derajat atau 2 persen.
Aspek (aspect) Aspek permukaan adalah arah dari perubahan z yang maksimum ke arah bawah. Aspek dinyatakan dalam derajat positif dari 0 hingga 360, diukur searah jarum jam dari Utara.
5. Turunan DEM
lanjutan
Analisa volumetrik volume menghitung luas dan ruang volumetrik antara permukaan dan harga datum yang ditetapkan. Volume parsial dapat dihitung dengan mengatur datum untuk sembarang harga yang lebih besar dari harga z minimum.
5. Turunan DEM
lanjutan
Analisa visibilitas Visibility mengidentifikasi pencahayaan (exposure) visual dan melakukan analisa pandangan menyeluruh pada suatu permukaan. Titik-titik pengamatan didefinisikan oleh feature titik dan garis dari satu coverage dan bisa menunjukkan lokasi menara pengamatan di tempat-tempat yang menguntungkan. Visibility mempunyai banyak pilihan atas kontrol parameterparameter yang diamati : spot, offseta, offsetb, azimuth1, azimuth2, vert1, vert2, radius1, dan radius2.
Visibility
lanjutan
Visible Not Visible
Fill Sinks Fungsi fill sink menghilangkan depression atau sink yaitu kondisi dimana terdapat perbedaan elevasi yang mencolok dengan cakupan yang sangat kecil.
(a) Sink
(b) Setelah proses Sink atau Filled sink
6. Kualitas DEM
Akurasi keseluruhan DEM : δt2 = δM2 + δS2
1. Ketepatan pengukuran (δM2) a. Skala dan kualitas data b. Kualitas peralatan c. Kualitas pembacaan operator 2. Pengaruh dari sampel (δS2) a. Kerapatan sampel b. Pola sampel
6. Kualitas DEM
lanjutan
1. Ketelitian (accuracy) ditunjukkan dg. Nilai RMSE, rata-rata absolut, atau standart deviasi
2. Ketelitian dalam perekaman (fidelity) terkait denan konsep generalisasi dan resolusi, ditentukan oleh : • perubahan medan yang tidak mendadak : ukuran grid atau CI, spasi titik dan akurasi planimetris • breakpoint dan breaklines – perubahan minimum lereng, panjang minimum garis
3. Tingkat kepercayaan (confidence) pengukuran untuk kualitas semantik data
5. Kualitas DEM
lanjutan
4. Kelengkapan (completeness) tipe kenampakaan yang disajikan : igir, pola drainage, puncak, lubang, permukaan air, dsb.
5. Validitas (validity) tanggal sumber data, verifikasi data seperti : cek lapangan, perubahan bentuk di lapangn
6. Tampilan grafis (apperance of graphics) varisasi warna, simbol, dan anotasi
6. Kualitas DEM
lanjutan
7. Aplikasi DEM I. ANALISIS MEDAN Analisis medan meyangkut data ketinggian (topografi) 1.1. Geomorfologi Geomorfologi secara quantitatif mengukur permukaan medan dan bentuk lahan : - Kemiringan lereng - Aspek - Kecembungan dan kecekungan lereng - Panjang lereng Hal tersebut penting untuk kerekayasaan yang menayangkut data tinggi : - Penggalian : volume - Manajemen lahan : site selection - Proses geomorfologi : erosi, landslide, aliran salju (modelling dan monitoring)
1.2. Hidrologi - Aliran runoff - Estimasi volume reservoar - Pemodelan banjir dan sedimentasi - Batas DAS - Pola aliran : 90% DAS di New York ditentukan dengan DEM
Peta Perbandingan Batas DAS dari keempat sumber data
Peta perbandingan Jaringan Sungai DAS Opak
What are DEMs used for?
7. Aplikasi DEM
lanjutan
1.3. Klasifikasi penggunaan lahan DEM membantu klasifikasi penutup lahan dengan mengkaitkan data kemiringan dan aspek yang dilakukan pada data LANDSAT MSS. Akurasi pengenalan meningkat dari 46% menjadi 75% dengan kombinasi citra LNDSAT MSS dan DEM. Penentuan penutup lahan (jenis tanaman) berdasarkan ketinggian 1.4. Pemetaan kontur - Pembuatan kontur dengan variasi CI 1.5. Komunikasi - Lokasi Pemancar telepon seluler - Pemancar TV 1.6. Keteknikan sipil - Rute perpipaan - Transmisi kabel listrik - Desain, konstruksi, dan pemeliharaan Jalan, jalan KA, airport, pelabuhan, saluran air/kanal, DAM
7. Aplikasi DEM
lanjutan
1.7. Militer - Sistem senjata pertahanan - Pendaratan pasukan 1.8. Arsitektur - Desain dan perencanaan Landscape kota
7. Aplikasi DEM
lanjutan
II. KOREKSI DATA DEM untuk koreksi citra satelit dan FU karena pengaruh topografi. DEM untuk orthophoto FU, DEM untuk koreksi citra Radar karena pengaruh layover pada medan perbukitan DEM baik untuk koreksi aeromagnetik, grafitasi, pengaruh ketinggian pada survey spektrometer III. VISUALISIASI Visualisasi yang baik untuk menggambaran medan dengan pandangan perspektif dan blok diagram. Teknik dapat dengan mengkombinasikan data lain (integrasi dan registrasi SIG) Contoh : visualisasi peta PL dengan peta shadow, colordrape peta-peta tematik
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