22/05/2014
DENGAN GPS
GPS : Global Positioning System Sebuah system yang dapat menunjukkan posisi benda di permukaan bumi secara cepat, di semua tempat, pada semua kondisi dan pada setiap waktu.
GPS : merupakan perkembangan paling modern sistem navigasi kuno •GPS dikontrol oleh U. S. Department of Defense (DOD).
1
22/05/2014
OLD MAP
Sistem yang menandai dimana posisi mereka, dan yang menunjukkan kemana mereka pergi, serta bagaimana jalan mereka pulang.
Navigasi kuno : Penghuni gua memberikan tanda pada dinding gua pelaut berpegangan pada posisi bintang Navigasi Kompas : memberikan arah utara
Sextant
Navigasi Sextant : memperkirakan sudut tinggi bintang, bulan dan matahari di atas Horison
Kombinasi Kompas dan sextant banyak dipakai untuk pelayaran, kelemahannya adalah bahwa dengan alat tersebut masih kesulitan dalam menentukan posisi garis bujur
Chronometer :
Mampu memberikan informasi posisi garis lintang (lintang utara/ lintang selatan) Ground-based radio-navigation systems :
Akurat namun cakupan areal sempit Sistem ini banyak dipakai pada waktu PD II Chronometer GPS :
Satellite-based radio-navigation system (high-frequency radio wave with a special coded signal) : cakupan area sangat luas GPS banyak dipakai dalam operasi Dessert Storm (9000 buah) Satelit GPS
2
22/05/2014
•
Space segment, (24 Satelit)
•
User segment (Pesawat, kapal, mobil,
• Monitor segment (Hawai, Diego Garcia, dan Colorado)
Ground Control System •
(Falcon Air Force Base in Colorado Springs, Colorado)
Space segment
3
22/05/2014
Control segment
User segment
SATELIT GPS GPS didukung oleh 27 satellite (data tahun 1998) Pada ketinggian 20200 km di atas permukaan bumi Setiap Satelit membutuhkan 12 jam untuk memutari bumi. Masing-masing dilengkapi dengan jam dengan akurasi yg sangat tinggi (0.000000003 detik)/ 2 cesium + 2 rubidium clocks Berat satelit : 930 kg, Panjang : 5.1 meter Kecepatan : 4 km/detik Umur satelit : 7.5 tahun
4
22/05/2014
How GPS Works trilateration
Prinsipnya adalah : Satelit GPS memberikan informasi kepada receiver GPS mengenai jarak/ posisi satelit. Sehingga kita tahu bahwa kita berada pada suatu radius tertentu dari satelit.
Bila ada dua satelit maka kita tahu posisi kita, berada pada 2 lokasi, yaitu perpotongan dua radius tadi. GPS receiver mampu menghitung tempat yg paling mungkin. Semakin banyak sinyal satelit ditangkap semakin teliti satelit menghitung posisi --- metoda Trilateration
3 satellites for a position fix
5
22/05/2014
Distance= velocity * travel time Distance is about 22,000 km
We cannot see satellites We cannot measure exact distance
Calculating distance to satellite Using travel time of radio signal Travel time = ? approx. 0.07 sec !
Using radio signal to calculate distance This signal travels with speed of light Speed of light = 299,174 km/sec
Very precise clocks for exact timing satellites
: highly accurate ‘atomic’ clocks
(about USD 100,000 each) receivers
: moderately accurate quartz clocks
Clock error due to difference in clock accuracy use a 4th satellite to correct for clock error
6
22/05/2014
Correcting for clock errors in 2D:
At least: 3 satellites for 2D fix 4 satellites for 3D fix
Geometric Dilution Of Precision (GDOP)
GOOD GDOP ( 2)
POOR GDOP (2-6)
7
22/05/2014
•Geometric Dilution of Precision (GDOP) and Visibility
GDOP, continued
We’re somewhere in this box
At close angles the box gets bigger
8
22/05/2014
GDOP, continued
GOOD COMPUTED GDOP AND BAD VISIBILITY RESULTS IN POOR GDOP
Selective Availability (SA) The US military can introduce intentional errors to limit accuracy for civil GPS users SA introduces an artificial clock error into the radio signal and writes an error in the satellite status information If SA is ‘on’ a potential horizontal accuracy of ± 30 meters will be reduced to ± 100 meters.
9
22/05/2014
Some typical errors Satellite clock error Receiver noise Interference in ionosphere and troposphere Multipath error Satellite position (“ephemeris”) error
± 2 meter ± 0.5 meters
poor GDOP Human errors Receiver errors (hardware, software, antenna)
up to 200 meters up to hundreds of meters
± 5 meters ± 1.4 meter ± 2 meters
any size possible
10
22/05/2014
Phase Differencing Techniques Teknik ini digunakan untuk menambah ketelitian pengukuran.
Single Differences
Diperlukan Reference Station GPS yang sudah diketahui posisinya, dengan merefer data tersebut GPS yang mobile, dapat memperkirakan posisinya dengan lebih tepat. Posisi Reference Station GPS dapat satu tempat atau lebih Teknik pengukuran seperti ini disebut DGPS : Differential GPS
Double Difference
11
22/05/2014
Navigasi Kapal dengan menggunakan 4 Reference Station GPS
GPS Error Sources • Noise
: Gangguan pada signals
• Bias
: Selective Availability (SA), Multipath, Delay oleh Ionosphere dan Troposphere
• Blunder : Kesalahan user (kesalahan datum, kesalahan komputer pada segment kontrol)
12
22/05/2014
GPS Error Sources
Selective Availability (SA) The US military can introduce intentional errors to limit accuracy for civil GPS users SA introduces an artificial clock error into the radio signal and writes an error in the satellite status information If SA is ‘on’ a potential horizontal accuracy of ± 30 meters will be reduced to ± 100 meters.
13
22/05/2014
Some typical errors Satellite clock error Receiver noise Interference in ionosphere and troposphere Multipath error Satellite position (“ephemeris”) error
± 2 meter ± 0.5 meters
poor GDOP Human errors Receiver errors (hardware, software, antenna)
up to 200 meters up to hundreds of meters
± 5 meters ± 1.4 meter ± 2 meters
any size possible
Typical accuracy: ±10 m Horizontal ( civilian use, good GDOP) Results of measurements over one month (Garmin 12XL) Horizontal Accuracy (50%) ± 3.9 meters Vertical Accuracy (50%) ± 9.6 meters Horizontal Accuracy (95%) ± 9.3 meters Vertical Accuracy (95%) ± 21.9 meters Source: GPS ACCURACY MONITOR by Dennis Milbert (http://mywebpages.comcast.net/dmilbert/handacc/accur.htm)
14
22/05/2014
To sumarize
1. Resection from satellites 2. Distance to satellites
4. Position in space
Basic
3. Exact timing
5. errors
buttons:
change up/down
Enter
Next page
Power
15
22/05/2014
Navigation
screen:
Mode Expected sat position
Accuracy Units Horizon
Battery level Known sat position
Skyline at 45º Zenith (90º) Signal strength
Satellite number
Data
Collector teknologi berbantuan komputer (mini) genggam sebagai antar muka (interface) dengan alat ukur elektronik
16
22/05/2014
Where Do You Need to Be? 30cm/1ft
5m
1cm
10cm/4in
1m
17
22/05/2014
GPS Accuracy Is GPS Accuracy important to you?
35
GPS Scatter Plots
36
18
22/05/2014
19
22/05/2014
20
22/05/2014
21
22/05/2014
22
22/05/2014
23
22/05/2014
24
22/05/2014
25
22/05/2014
26
22/05/2014
27
22/05/2014
28
22/05/2014
29
22/05/2014
30
22/05/2014
31
22/05/2014
Rekonstruksi batas tanah (persil) Langsung
32
22/05/2014
Rekonstruksi batas secara tak langsung
33
22/05/2014
34
22/05/2014
35
22/05/2014
36
22/05/2014
37
22/05/2014
38
22/05/2014
39
22/05/2014
40
22/05/2014
41
22/05/2014
42
22/05/2014
43
22/05/2014
44
22/05/2014
45
22/05/2014
46
22/05/2014
47
