Rabu, 31 Disember 2008
Translating this into the GPS world, we can replace the known points with satellites, and the azimuth with time taken for a signal to travel from each of the known points to the GPS receiver. This enables the system to work out roughly where it is located - it is where the circles representing the distance from the satellite, calculated on the basis of the travel time of the signal, intersect. Of course, this requires that the GPS locator has the same coordinated time as the satellites, which have atomic clocks on board. To do this, it cross-checks the intersection of the three circles with a fourth circle, which it acquires from another satellite.
If the four circles no longer intersect at the same point, then the GPS system knows that there is an error in it’s clock, and can adjust it by finding one common value (one second, half a second and so on) that can be applied to the three initial signals which would cause the circles to intersect in the same place. Behind the scenes, there are also many complex calculations taking place which enable the system to compensate for atmospheric distortion of the signals, and so forth, but the principle remains the same.
Originally conceived as a navigation aid for the military, the Global Positioning System, or GPS, has since grown from relatively humble beginnings as different supporting technologies have been developed, some off which are within reach of consumer budgets. All that GPS does is provide a set of coordinates which represent the location of the GPS unit with respect to its latitude, longitude and elevation on planet Earth. It also provides time, which is as accurate as that given by an atomic clock. The actual application of the GPS technology is what leads to such things as navigation systems, GPS tracking devices, GPS surveying and GPS mapping. GPS in itself does not provide any functionality beyond being able to receive satellite signals and calculate position information. But it does that very well
Ä Base station.
Ä Rover station.
Ä Radio link.
It uses a network of fixed ground based reference station to broadcast the difference between the positions indicated by the satellite system and the known fixed position. This station broadcast the difference between the measured satellite pseudo range and actual (internally computed) pseudo range, and receiver station may correct their pseudo range by the same amount. This correction will be sent by radio link.With DGPS, position accuracy is improved, going from 30 metres to better than 10 metres. This system requires at least 2 GPS instruments (receivers & antennas) transmitting positions from at least 4 GPS satellites. 1 GPS instrument set up on a base station with known position and the other 1 set up on a static or dynamic rover station with unknown position.
Suppose a GPS receiver turned on and picks up the signal of 1 satellite. The receiver tells the location of the satellite and the distance between the receiver and the satellite. But this single measurement is not a big help. At best, we can conclude that the point position given is within a rather large circle whose circumference is determined by the distance from the satellite. We are still lost.
· 2 satellites.
Now suppose that the GPS receiver picks up signals from another satellite. This helps to narrow down the location and the location is somewhere within the intersection of 2 large circles. We still do not know the exact position of the point, but things are starting to look better.
· 3 satellites.
Let’s go one better. If the receiver picks up signals from a third satellite, then the position will be known to be within the intersection of 3 circles. Now we have the position but no check on its quality.
· 4 satellites.
With 4 satellites we will get a precise point for the position and also the elevation. Here, we have a position that is accurate to 30 metres.
= Usually used the vertical datum from established BM.
LSD is differing from MSL because reduced level from established BM is referring to MSL at Klang Port.
=Reduced sounding refer to LSD can merge with land details refer to vertical datum from established BM.
=This is the datum plane adopted by the national authority for its published chart and tidal predictions.
= The datum only is used around of tidal observation.
= It is different at different locations.
= Depends on the range of tidal or water level.
= It will only be the same as the SD when the Hydrographic Office has analyzed the survey data and confirmed the suitability of field surveyor’s choice. The surveyor cannot establish CD in field.
= CD is defined by the International Hydrographic Bureau (IHB) as a level below which the tide will but seldom fall.
= In none-tidal waters, CD is normally established at MSL.
= Because LAT is so difficult to define precisely, CD for Admiralty and Australian charts has been more broadly defined as the level below which no predicted tide shall fall more than 0.1m.
= It is the datum which the field surveyor will establish and adopt.
= Ideally SD should be the same as Chart Datum (CD), but may well differ particularly when the original survey is very old.
= One of these methods is to be used when establishing datum;
· Recover a previously established SD or CD in the survey area by leveling from benchmarks.
· Transfer datum from a place close to the survey area where CD or SD is already established, by taking simultaneous tidal observations over a period.
· Establish a new datum from observations.
= There is no simple formula or rule available to calculate LAT from observations or tidal constituents.
= It can only be obtained properly by studying tidal predictions covering several years (18.6 years ideally), as level of LAT will not be reached every year.
= MTL is defined as the mean of all HWS and LWS over a period of time.
= It is not (at present) possible to convert simply from MSL to MTL (or vice versa) at any point.
= MTL and MSL will only coincide when tidal curve is a perfect sine curve and this rarely occurs.
= MSL is the natural reference level of the geoid, and is defined as the average level taken up by the sea along a long period (18.6 years if possible).
= In practice it is obtained from the mean of all tide readings or MSL is the average level taken up by the sea.
= It coincides very nearly with the geoid.
= The accuracy of MSL depends on a long period of tidal observation.
= The best result can be obtained with 18.6 years observation.
= MSL is the best vertical reference level we have and as such is the basic reference level for tides.
= Observed MSL is subject to change due;
· Polar melting or glacial activity.
· Meteorological effects (rain, wind, pressure).
· Short period effects (sea, swell, surges, etc.).
· Tectonics (crustal changes).
· Astronomical effects (changes in MSL due to the combined effect like seasonal meteorological variation).
· Mean of all tide readings over a long period (30 days to 18.6 years).
· Multiple of 25 hourly observations (preferably 3 days to 75 hours).
· Mean of 25 hourly observations (poorer value).
Sabtu, 13 Disember 2008
Khamis, 11 Disember 2008
Selasa, 25 November 2008
Khamis, 20 November 2008
COMPUTER APPLICATION I
= learn about programming
= Microsoft excel
= what is computer?
= chain survey
= compass survey
= plantable survey
= introduction make the traverse using thedolite
= bearing and angle
ENGINEERING SURVEYING I
= basic principal of EDM
= the wave from total station
= what is lavelling?
= how to perform this practical?
= make the traverse and take the detail around control
= cross set n long set
CADASTRAL SURVEYING I
= theory about partition,sub-division,amalgation
= how to prove the datum…
= practical : make a new lot
= study of time around the world
= gerhana bulan dan matahari
= practical: solar observation
COMPUTER APPLICATION II
= learn how to using solfware:
1) CDS(civil design n survey)
2) Autocad 2004
= combination autocad n CDS
ENGINEERING SURVEYING II
= setting out
= mine survey
= practical: traverse,make the detail,cross set n long set, and process the data using solfware….
CADASTRAL SURVEYING II
= first alienation of survey
= base line
= right of way
= cadastral processing system
= road reserve
= F2F concept..
= party wall survey
= practical: sub-division work
Isnin, 27 Oktober 2008
Ahad, 26 Oktober 2008
Kebiasaannya, garis asas digunakan dalam kerja tanam pastian untuk ukur kadaster. Konsepnya adalah bahawa nilai lama yang dicerap dari pelan akui dan nilai baru daripada pengukuran terbaru berada di dalam satu kedudukan. Oleh itu,nilai lama akan dilaras bagi membolehkan kerja-kerja tanam pastian dilakukan. Sila muatkan dalam minda bahawa garis asas adalah sebahagian daripada datum yang diguna pakai ukur kadaster iaitu penggunaan 3 batu sempadan, 2 batu sempadan dengan cerapan matahari ataupun system pendudukan sejagat (GPS). Semasa membuktikan nilai pengukuran baru dan lama,adalah jarang untuk mendapati nilai kedua-duanya adalah sama ataupun tepat kerana setiap juruukur adalah berbeza. Sebagai contoh apabila sesuatu lot diukuresuatu lot diukur berulang kali, ketepatannya mungkin melebihi ukuran kelas pertama. Langkah seterusnya adalah orientasi dan pengskalaan. Nilai ukuran lama contohnya perbandingan antara nilai baru dan nilai lama terdapat perbezaan samaada bearing dan jarak (-30” perbezaan bearing dan 0.004 adalah perbezaan jarak). -30” bermaksud yang perlu dilakukan pada setiap garisan dalam ukuran lama manakala 0.004 m adalah nilai tutupan lama dan baru. Pengskalaan adalah melalui pendaraban nilai garisan lama yang tertentu dengan jumlah jarak baru yang dibahagi dengan jumlah jarak terlaras. Orientasi dan pengskalaan adalah bertujuan untuk melakukan tanam pastian kerana nilai jarak dan bearing adalah berkaitan samaada nilai pengukuran baru dan nilai pengukuran lama. Orientasi & pengskalaan adalah kata kunci bagi penggunaan garis asas dalam ukur kadaster. “maklumat diterbitkan melalui pendapat daripada Mr Idham Lai(surveyor) daripada syarikat Juruukur semasa, MELAKA”
Ahad, 19 Oktober 2008
Format A-Rectangle shape (graphic area)Format B-Horizontal shape (graphic area)Format C-Vertical shape (graphic area)Refer to JUPEM circular 6/1998.
The criteria is as belowFormat A1.
Minimum margin (up&down / left&right) : 13.5mm / 15mm2. Space for test : 80mm x 270mm3. Space for graphic : 270mm x 310 mmFormat B1.
Minimum margin (up&down / left&right) : 15mm / 13.5mm2. Space for test : 390mm x 80mm3. Space for graphic : 390mm x 190 mmFormat C1.
Minimum margin (up&down / left&right) : 13.5mm / 15mm2. Space for test : 80mm x 390mm3. Space for graphic : 190mm x 390 mmSize of A3 is 297mm x 420mm.