Geoid - Although irregular surface - but it represents the true shape of the land , whichWe live .... To represent any area on the maps , we measure on the ground and realThat can express them geoid surface ..... The problem is that this surface is irregular andSevere aliasing and has no mathematical equations or mathematical laws to describe its surface and thusVeto the maps even express the terrain carefully ... so the solution isThe use of any mathematical model known ( his mathematical equations to describe it ) in the work of creationMaps and here it must be a way to convert between this surface and the geoid mathematicalTheoretically, ( Mil Alalpsoیd ) .... A measurement is directly on the AlalpsoیdFor it does not exist in nature, it is assumed the surface of my closest geometric shapesJیoیd the ground or in real .... The surface topography of the land , it is in reality isGeoid itself if it does not Nakhzd in mind heights and depressions in the mountains , anyThe geoid is a simplification of the surface topography of the land and is therefore irregular and has noMathematical equations for the recipe and make it accountsThe problem is a simplification : Our true shape of the land on which we live , and makeMeasurements by ( geoid ) but it does not fit in with the accounts and bring down the maps , and we have a surfaceAthletic regularly ( Alalpsoیd ) suitable for calculations and charts but it is not actually present in theNature and measurement can not it .... So it must be a way to convert measurementsCadastral that has on the ground ( geoid ) to the corresponding Ali Alalpsoیd even can create accurate mapsTypes of gains :There are several references to altimetry , which in turn determine the types of gains . If were to take the average sea level will rise as a reference output is fromWhich we refer to as the word is generally attributed to a user in the topographic maps in most countries. The Orthometric Height kind AlarzmitriThis is the kind of heights Geodetic Height if we adopted the reference surface Alalpsoیd type height at which we get the so-called rise GeodeticFor example . There are also other types of elevations . GPS output of MeteorologyAltimetry in a vast region - especially inBusiness that do not require high accuracy - it is possible to useBecause it is faster and easier and cheaper but GPS MeteorologyMust in this case type conversion to rise GeodeticEven attributed to agree with old maps of the area orWith maps of the state in general. Here we must be a modelJیoیd allows switching between both types of gains .For Ahlیj or Alalpsoیd or anthropomorphic ellipse or shapeOval or Alasafaroیd (all names for the same thing anyThey are all synonymous ) in general is a model to represent the size andShape of the planet . Any attempts to answer the question: What is theShape of the earth as long as it's not a ball full rotation ? IfThe shape of the earth is oval shape - any closerHave a form of a hen's egg - What is the size of the egg ?Is it big or small or medium ? .... In order to answer this question you should know the value of these two elements that determine the size of the egg ( or size Alahlیj ) : (1) whatAxis passing through the poles ) ? If we set these ) b axis passing through the equator line ) , (2) what is the value of the smaller half -axis ) a half -axis is the value of the largestValues ​​will determine the size and shape of Alahlیj want to use later in the process of creating maps.Vmaaml splaying ... b instead of determining the value of a half -axis smaller flattening determine the coefficient of splaying + a also can determine the value of half of the major axisCan be calculated from the equation : f callf = (a - b) / aTo determine the size Alahlیj . a and f or the values ​​of a and b we can use any valuesIn order to calculate either of these two values ​​shall scientists collect spatial measurements ( distances and angles and astronomical and meteorological observations attractive floor ..... etc. ) have been measuredAnd of course we need to measurements of ..... (a and f or value ) a and b in multiple regions of the whole earth and enter this data into a computer program calculate the value ofThe whole earth from these accounts is the international scientific community specialized in space and not private individuals .Again it would be different from a, b ​​, then we get a new spatial measurements or modern ? If we calculated the values ​​of a, b ​​come the following problem if we accountIn 1880 he fired his name on a, b ​​the first time and probably the most accurate of them ... From here came the idea of ​​having more than Ohlیj ..... Clark as an example of the world by valuesIn 1906, also named Ali fired this Alahlیj second , ... and so on .... Then I started body a, b ​​.... This Alahlیj Came another world named by Hlmert and valuesThen the latest global Ohlیj a WGS International Geodesy at the expense of Ohlیj recommends its use in all countries of the world appeared to be a unified global Alahlیj 72It is what can be considered the most accurate model Ohlیj represents the shape and size of the planet , the world body and recommended that this be Alahlیj is approved for the world WGS84In any coordinates measured by this model were adopted WGS 84 GPS Alahlیj of America when it developed the technology WGS whole fame came Ohlیj ..... 84Technique, that is, the coordinates of any location Oqیsha with backhaul UPS be supported on this Alahlیj .Here, the second problem : If the state had adopted the model Ohlیj Old in the production of maps and then appeared the most accurate model of it , would change all maps ? Of course not .. because theyWGS is different from the process will be expensive material strongly .... Or how the state would benefit from measurements backhaul UPS as long as these coordinates depend on Ohlیj 84Ohlیj maps of this state ? ...... Scientists studying the area and found the problem solved : If we can determine the relationship between different Ohlیjیn we canTransform coordinates measured on a one to the values ​​corresponding to the other ... and Alahlیj study , scientists found that the relationship between any Ohlیjیn is the 7 Elements
First: Do Central Alahlیjیn Mntbakیn or one away from the center of the other? What is the value of this away , or the difference between the two centers ? To measure the difference must be hashed toIf ...... X, Y, and Z axis 3 compounds trends in three axes : the x-axis , Y-axis ( axes Alavqییn ) , p axis ( vertical axis ) orThere is a difference between a central or move away Alahlیjیn must select three values ​​( of the three axes ) that describes this difference , and this is what we call the transactions or stay awayTranslation Parameters: dX, dY, and dZX, Y, Z Second: Is Alahlیjیn axes parallel axes or that one oblique axes Alahlیj second ? What is the value of this tendency among the three axes of each OhlیjAll three axes of Ahlیj other? Therefore, you must know the value of 3 -axis angles for miles for the first and second ... This is what we call the axis of rotation transactionsRotation Parameters Rx, Ry, and RzThird: Is the size of the first Alahlیj equal to 100% the size of Alahlیj second or one that is smaller or slightly larger than the other ? ..... If the calculated distance between two points two pieces of informationa, and b) to him ) and then calculated the same as the distance between two points using the same transactions Alahlیj II a, and b Alahlیj using the first (ie, using valuesScale for the second ) Will it be equal distances with accuracy or coefficient of variation , even if there is a simple between them? This factor ..... is what we call coefficient measurement orfactorSo : We have 7 elements must know their values ​​in order to half of the relationship between any Ohlیjیn (3 away and 3 rotation and scale factor spaces) .... If we know the values ​​of these elementsSeven can turn coordinates ( longitude and latitude and altitude ) as measured on the Ohlیj to the values ​​corresponding to them on the second Alahlیj .Question that occurs in people's minds now is how do we calculate the values ​​of conversion between Ohlیjیn ? The answer is to get on some common points of informationYou must know the coordinates of some points in the WGS coordinates Ohlیj all of them .... If I want any account transactions conversion between Ohlیj Clark 1880 Ohlیj 84Alahlیj in the first and second Ahaddatیathm in Alahlیj , and using mathematical equations can be calculated elements of conversion.But - as stated in the table in your message - maybe more than I find values ​​for the elements of conversion between the same Alahlیjیn ? How did this happen and who is better or more accurate ? ....There are three reasons for the differing values ​​of transactions :1) the base first sports provides that to calculate the conversion factors between Ohlیjیn should I get 3 points in common , at least ( any one point is not enough )And not even two points ) .... If we had 4 points in common Astkhaddmnahm in the accounts would be more accurate results than using only 3 points ... and so on : the greater the number ofPoints shared information more accurately calculated transactions ....2) The second reason is the quality or accuracy of the coordinates of points in common: If used in the calculation points coordinates inaccurate Alahlیjیn one of the transactions )Calculated will not be accurate and also vary the value of the situation , which used the points of known coordinates PRECISION ..... and this is the cause of the difference accuracy transactionsWhere GPS often face this problem in converting Meteorological ... eX, eY, and eZ conversion table in your message , which appear in the last three columnsBe very high accuracy coordinates (sometimes millimeters ), while the accuracy of the coordinates of the same points shared in the national system less ( Dیsیmtrut only) resulting in transactionsThe conversion is not high -res3) The third reason is the location of points in common : it is possible to find two neighboring states have adopted a particular Ohlیj - such as Clark in 1880 , for example - in the system Ahaddatیathm )But the common points between Alahlیjیn will be of locations or in different areas , which will make the conversion factors calculated in a different value of a country or regionEach special group WGS state to another ... and this is found in the table where we will find more than one set coefficients to convert between 1880 and Clark Ohlیj 84Certain ( Senegal , Sudan and Burkina Faso ..... etc. ) .Also - and in response to one of your questions - point out that when he figured out the elements of conversion between the seven Ohlیjیn to a particular region or country does these elements will be the sameAccuracy in all parts of the country or geographical area ? .... Often specialists in the space geodetic who calculates the elements of conversion of each geographical region( Medium size ) on my own and it is not logical that figured 7 are all elements of the state .... A lot of Masters and PhD who has studied thisSubject and proved that the best elements of the account of each part of the state instead of the elements of one of the state because the whole accuracy will vary from one region to another and this method .....It has many publications in this NGS known as National Geodetic Survey is used in the form of United States Geodetic SurveyArea available on its website ...... But if calculated for the seven elements of a large area - such as Saudi Arabia also came your message - the accuracy will not be good ateX, eY, throughout its , and as you can see in the table contained all the elements of your message reference slave named the accuracy of these elements ( the last three columns in the table2 meters of each region. - Amounting to 10 meters , while if fragmented Arabia for a number of areas and elements of the conversion calculated for each region , it is possible that out of accuracy to 1 (eZAll of the above , and we are talking about coordinates measured on the surface of the earth (ie, longitude and latitude and altitude ) Ohlیj whether on a national or global OhlیjAnd how to turn them ....... But we are in the maps we convert Coordinates measured on the surface of the ground or Alahlیj three-dimensional to the corresponding coordinatesIt is not anthropomorphic , that coordinates on the map ( two-dimensional ) plane is not represented on the map .... As is known, the map is a levelAre exactly the coordinates that we measured on the ground or anthropomorphic Alahlیj ..... how will it change these coordinates ? And any value ? .... This is the science of projection maps or
map projectionThis has nothing to do directly Alahlیj change from one type to another .... Words, if the same Alahlیj - Clark in 1880 , for example - and you measure the coordinates of a certain point How doSasagt this point on the map based on the same Alahlیj ? Is Coordinates Sasmha observed in nature as it is - a scale drawing - on the map? PrintThe answer is no ... because the earth model whereas the level of the map and therefore must be the values ​​of Coordinates be changed a little when you drop it on the map .... Once again, I assureThe point : we use the same Alahlیj measurement field and also in the mapping ....So the projection has nothing to do - so far - the kind Alahlیj user .... There are too many kinds of mathematical methods used in the projection maps , such asProjection plane and cylindrical and conical ... and within each group there are several types of projections also .... And even in the same type of projection begins in each stateChange it to suit the geographical area ....For example : Is the center of the projection system will be the center of the earth , or it is better to define the state in the center of the projection points within the geographical boundaries ? .... Is the goalProjection maps at the whole world , it is logical that I set the center of the projection is the center of the earth , but if the objective of establishing a system to drop the Local certain state mustTo be centered within the state because of the fundamentals of projection maps that error ( or what we call the deformation map ) will be zero at the center and begins to increase wheneverLocated approximately in the (point of origin after us for this basic point ... permission for a particular state does not have to be the center point ( or what we call the point of originThe middle of the geographical boundaries of this state in order to be wrong , or what could be less deformation maps in this state ..... and center projection is determined by a country'sTransactions in Central Meridian and Latitude of Origin determine longitude and latitude point at which the center will consider as it is what we callProjection ......Then comes the second question : What are the coordinates of the center point of the projection ? I would give you the coordinates of zero , zero like any graph or want a new map drawn ? If theThis central point in the middle of the geographical boundaries of the state , it will lead to the existence of a negative coordinates to some areas of this state , and this situation unpleasantlyCoordinates and maps in general because it could lead to some errors if neglected - without being mean - negative sign in the coordinates for that point .....Preferably in most states that all the coordinates of locations within the state a positive signal for ease of handling and ..... here instead of the site to change the point of origin IImposing coordinates - not true - in order to get her in the end, the coordinates of each positive parts of the country .... For example, instead of coordinates = zero , zero point..... False Easting and False Northing coordinates 1000 .... His is one of what we call , originally suppose its coordinates = 1000All that remains for us , but the same answer the last question that we talked about earlier which is: if the distance is measured from the map and hit the drawing scale output isWill be equal to the distance measured in the field in real 100% or there is a difference in the distances ? ... Because of the projection process itself often there will be a differenceFor this type Scale factor in the spaces between the map and the true reality , and the ratio between the distance on the map to the real value we call the coefficient measurement orProjection .........This means that the final conclusion is :Established the system in order to drop the special country-specific I must specify values ​​are 5 elements : site main point or center of projection and coordinates this point and coefficientMeasurement ........ every state to choose values ​​of these five elements of the projection system which you want to apply .... It is not possible to declare the state of these values ​​and the values ​​are within the confidentialityThe government agency responsible for the maps , which are often on the military operation in most Arab countries ......... again and again : Choose a projection system has nothing to doDirectly Ballahlیj values ​​will differ if different elements Alahlیj user .... Relationship here indirect relationship : the sense that the coordinates of the point of origin of the projection systemWhat Alahlیj which was calculated these coordinates it? .... If the point of origin is known Central Meridian and Latitude of OriginCoordinates Ali Ohlیj Clark in 1880 , the projection system of this extension will be supported on the same Alahlیj ... in the sense that in the process of calculations and map projectionClark Ahlیj to 1880 , the resulting map will be - implicitly - a and b are supported for Ahlیj , if we substitute the values ​​of a and b would intervene in the elements of equationsAli Ohlیj Clark in 1880 ...... and so it is possible to have the same projection system - Alstrیogerafa for example - and the same Alahlیj - Clark in 1880 , for example - usingIn more than one country has the coordinates completely different ! ! ! How? Because each state will have them drop the elements ( the five elements ) for different elements used by theClarke for 6 different types of the same type of projection 1880 ArcMap other state .... This is the answer to your question about the presence of 6 files in the programSo ..... here is not the difference in the type of projection, not in kind Alahlیj (all one of the six cases ) IGN, Benoit, Arc, RGS, SGA different names such asBut the difference is the values ​​of the five elements chosen by each country , resulting in multiple types of projection systems .We come to an important point in the message: that I could not see the five elements of the projection of a particular state What do I do ? Can I self-employed or their conclusions one way or another ?Unfortunately the answer : No! ! ! ! ! These elements have not been selected to be calculated ! ! There is not any way for her hence the confidentiality in every state ! ! All ITo do in such a situation is alien to experience more of the value of knowledge and error until the best values ​​out of the five elements .... I have a sense that if the coordinates of a realAnd change the values ​​in the tray and error of the measured points ( or set of points ) and the known spatial coordinates of the same point ( or points) on the map in the experiment neverElements and figured projection coordinates and point Oqarnha Bahaddatیadtha PRECISION information on the map central meridian and latitude of originTo know the difference , or error , and so many times until I get on the values ​​of the elements that give less differences Coordinates for information . .... There is no way else unfortunately ! !And God knows best and highest .The third part of the answer relation Baldatem or reference .... But before we start explaining the partial stress is very important : so far, we define the desired AlahlیjUsed for a particular country and also we were to how to determine the state of the components of the system without touching dropped to Aldatm ..... This shows that the choice of type and AlahlیjChoose the type and elements of the projection does not support - so far - and it has no direct relationship Baldatem .Hence the confusion in some of the questions asked , such as :The question before the amendment process ,, datum - who surely understood that when you are a country or a state amendment Seven ellipse parameters , it is called here DatemAlahlیlj seven parameters .. Let us take , for example, ellipse Clark Global 1880 .. How was the parameter values ​​of the seven .. Was zeros or what? Understood what you saidClarke 1880 is a global ellipse parameters seven .. When the state is modified depending on the circumstances , it has become a region is called Datem .You are here confuse the seven parameters of a special transfer to Ohlیj Ohlیj last among the five parameters that determine the type and elements of projection ! ! ! IfThere must be a values ​​for the elements of the seven (3 away and 3 rotation and scale factor ) between both whether one WGS took Ohlیj Clark 1880 and 84 OhlیjDatem to a particular country or is the only global Ohlیj .... Seven elements here to determine the relationship between both Alahlیjیn and how to transform the coordinates of points measured on the first AlahlیjCoordinates corresponding to the second Alahlیj .... Did we mention the word Datem never until now did not come into play never .... And therefore I can not say that the elementsSeven were = zeros before turning Alahlیj of a global model to Datem to state the company of ... elements have values ​​, whether due to Ahlیj Clark or 1880 for DatemClark relies on 1880 ..... this fundamental point must be well understood .... And therefore, you say that :Baramtruth equal zeroes right .. wgs his seven parameters differ from the others and that he only ellipse 84 (wgs -1 any ellipse in the world (not ellipse 84Global ( and which was built by the program Cockle Earth ) All the Baramtruth seven zeros is because it is the main Alahlیlj .. and here Ncbha wgs -2 course, the ellipse 84Like the main axes Coordinates right?Say is wrong ! ! ! Excuse me in this ...... again : seven parameters to convert between Ohlیj and last but not Ahlیj a particular .... None of the seven parameters OhlیjOhlیj to another . WGS but there are parameters for the conversion of 84 ! ! ! ! WGS84The idea Aldatm are:After selecting a particular global Ohlیj - Example Clark 1880 - to deal with him in a state , the state does not care that this Alahlیj about the true shape of the Earth in allOnhaaha , but more importantly for this state to have this Alahlیj quite similar to the shape and size of the Earth in its geographical boundaries , even if Say this symmetry or accuracy of the rest of theEarth .... The goal here is suitable to choose Ohlیj geographic regions to be more accurate cartographic what you can ..... here in this state amendment put Alahlیj (notTo be the best of what is in the region .... To imagine the situation with me : I'm going to raise or lower Alahlیj little touches the ground in the states (a and b in its dealingsNot a, b ​​, even if it leads to lifting Alahlیj deviate from the surface of the earth in the other half of the earth ... I will not change any of the shape or size Alahlیj ( the same valuesI replace it ), but I'll change of status slightly .... Example : There is a difference between the height of the surface and the surface of Alahlیj geoid ( true shape of the Earth) in all parts of the earthEqual to zero at the point (geoid undulation and this difference varies from place to place in the states ..... I will assume that this difference ( we call diffraction or geoidThis hypothesis as if I lifted Alahlیj even touches the ground at this point .... Now this new situation , Point of Origin originally projection systemAlahlیj is no longer the same as the previous position ( with the shape and size as it is not changed ) is no longer a global Ohlیj anymore but became Ohlیj him a special status when the states ....Clark 1880 Kohlیj global values ​​are invaluable to Clark a, b ​​Local and global Ohlیj not now ..... any definition of Datum values ​​, then we call it the word Datem1880 Kdatem in Syria, for example , but put disagree when it became Datem of this state , and this will be the seven conversion factors will vary also when I wantAnd between the WGS to this Aldatm ..... and this is the reason - an additional well - for the existence of differences in the conversion of the seven elements between 84 WGS transform the coordinates of 84Clark in 1880 in several countries , because each country uses its Kdatem Clark 1880 (ie, the amending put ) no longer is the same as the global Alahl