Prototype and description of the function coordtrans() (Function of the unlock requiring group "Coordinate Transformations") |

coordtrans() 2D Coordinate Transformation and Reference System Transition for numeric and alphanumeric coordinates with memory allocation for the return strings. Prototype of the DLL function in C++ syntax (attend lower case!): extern "C" __declspec(dllimport) unsigned long __stdcall coordtrans( double nCoordXQ, double nCoordYQ, const char *pszCoordQ, unsigned short nCoordSysQ, unsigned short nRefSysQ, double *nCoordXZ, double *nCoordYZ, char **pszCoordZ, unsigned short nCoordSysZ, unsigned short nRefSysZ, unsigned short nStripZ); Prototype of the DLL function in Visual Objects syntax: _DLL function coordtrans(; nCoordXQ as real8,; // 8 Byte nCoordYQ as real8,; // 8 Byte pszCoordQ as psz,; // 4 Byte, char* nCoordSysQ as word,; // 2 Byte nRefSysQ as word,; // 2 Byte nCoordXZ ref real8,; // 4 Byte nCoordYZ ref real8,; // 4 Byte pszCoordZ ref psz,; // 4 Byte, char**, 20 alloc. nCoordSysZ as word,; // 2 Byte nRefSysZ as word,; // 2 Byte nStripZ as word); // 2 Byte as logic pascal:geodll32.coordtrans // 4 Byte The allocation of memory for "ref psz" / "char**" is necessary only if setstringallocate(FALSE) is called before. The function converts the numeric source coordinates nCoordXQ and nCoordYQ or the alphanumeric source coordinate pszCoordQ from the source Coordinate System nCoordSysQ to the numeric target coordinates nCoordXZ and nCoordYZ or the alphanumeric target coordinate pszCoordZ of the target Coordinate System nCoordSysZ. For a both source and target coordinates either two numeric or one alphanumeric parameter will be passed. The transformation is accomplished with high exactness and great speed. The difference between the function coordtrans() and the function coordtrans3d() is that this is a 2D transformation. Thereby in the case of using different source and target Reference Systems the ellipsoidical height is not included in the calculation because it has only a very small influence to the position accuracy. The passed source coordinates and the calculated target coordinates are examined for the range validity within their Coordinate Systems and for syntactic correctness. The range validity is specified in the list "Defaults of the Coordinate Systems". The range and syntax check can be switched on or off with the function setcoordarea(). If in nCoordSysQ or in nCoordSysZ the values 1000 or 1100 are passed, the function uses the parameters of the user-defined Coordinate Systems passed before by the functions setusercoordsys1() and/or setusercoordsys2() and the earth ellipsoids defined before by the functions setuserellsource() and setuserelltarget() With the Coordinate Transformation a Reference System Transition from the geodetic Reference System nRefSysQ of the source Coordinate System can be considered to the geodetic Reference System nRefSysZ of the target Coordinate System. If in nRefSysQ or in nRefSysZ the value 0 is passed, then the geodetic Reference Systems, usual for the respective Coordinate Systems, are taken as a basis for the Reference System Transition. The standard Reference Systems are specified in the list "Defaults of the Coordinate Systems". If in nRefSysQ or in nRefSysZ the value 1000 is passed, the function uses the parameters of the user-defined Reference Systems passed before by the functions setuserrefsys() and the earth ellipsoids defined before by the functions setuserellsource() and setuserelltarget() If in nRefSysQ or in nRefSysZ the value 1100 is passed or if both parameters have same value (larger than 0), no Reference System Transition takes place. Then the earth ellipsoids, usual for the respective Coordinate Systems, are taken as a basis for the Coordinate Transformation. The standard earth ellipsoids are specified in the list "Defaults of the coordinate systems". If in nRefSysQ or in nRefSysZ the value 1150 is passed, no Reference System Transition takes place. Then the earth ellipsoids defined before by the functions setuserellsource() and setuserelltarget() are taken as a basis for the Coordinate Transformation. If in nRefSysQ or in nRefSysZ the value 1200 is passed, no Reference System Transition nor Ellipsoid Transition are performed. If for Reference Systems nRefSysQ or nRefSysZ no Reference System parameters are defined, only an Ellipsoid Transition is performed, but no Reference System Transition is performed. For transformations to the target Coordinate Systems Gauss-Krueger and UTM the meridian strip nStripZ, to which the target coordinates are to refer, can be given. The given meridian strip should not deviate more than 3 strips from the native meridian strip of the target Coordinate System. If in nStripZ the value 0 is passed, an automatic computation of the native meridians strip from the geographical length takes place. The following transformations are possible: Coordinate Transformations with maintaining the Reference System. Coordinate Transformations with Reference System Transition. Coordinate Transformation with Ellipsoid Transition when Reference System parameters not defined. Reference System Transition with maintaining the Coordinate System. Change of the notation (way of writing) with geographical coordinates. Change of the meridian strip with Gauss-Krueger and UTM coordinates. Conversion in the native meridian strip with Gauss-Krueger and UTM coordinates. The parameters are passed and/or returned as follows: nCoordXQ Longitude, East or X component of the numeric source coordinate. During processing of an alphanumeric coordinate this parameter is without meaning. The input format of the coordinate (notation) is described in the list "Defaults of the Coordinate Systems". nCoordYQ Latitude, North or Y component of the numeric source coordinate. During processing of an alphanumeric coordinate this parameter is without meaning. The input format of the coordinate (notation) is described in the list "Defaults of the Coordinate Systems". pszCoordQ Alphanumeric source coordinate. During processing of a numeric coordinate this parameter is without meaning. In this case for pszCoordQ a NULL pointer can be passed. The input format of the coordinate (notation) is described in the list "Defaults of the Coordinate Systems". nCoordSysQ Coordinate System of the source coordinates. (see list "Coordinate Reference Systems"). nRefSysQ Geodetic Reference System of the source coordinates. (see list "Coordinate Reference Systems"). nCoordXZ Longitude, East or X component of the numeric target (ref) coordinate. During processing of an alphanumeric coordinate this parameter is without meaning. The return format of the coordinate (notation) is described in the list "Defaults of the Coordinate Systems". nCoordYZ Latitude, North or Y component of the numeric target (ref) coordinate. During processing of an alphanumeric coordinate this parameter is without meaning. The return format of the coordinate (notation) is described in the list "Defaults of the Coordinate Systems". pszCoordZ Alphanumeric target coordinate. (ref) During processing of a numeric coordinate this parameter is without meaning. In this case for pszCoordZ a NULL pointer can be passed. The return format of the coordinate (notation) is described in the list "Defaults of the Coordinate Systems". Note: "ref pszCoordZ" corresponds to "char**" in C. 20 bytes of memory for the zero terminated string must be allocated with dependence to the call of the function setstringallocate(). Please consider the notes in the description of the function setstringallocate(). If the used programming language does not support the construct "pointer to a pointer to the first character of a string" (char**), then the function coordtrans2() can be used in place of the function coordtrans(). Further information can be found in the description of the function coordtrans2(). nCoordSysZ Coordinate System of the target coordinates. (see list "Coordinate Reference Systems"). nRefSysZ Geodetic Reference System of the target coordinates. (see list "Coordinate Reference Systems"). nStripZ Meridian strip to use. This parameter has only an effect, if a "Transversal Mercator meridian strip system" is registered in nCoordSysZ. 0 Calculation of the native meridian strip from the geographic longitude. › 0 Valid number of the required meridian strip. returnVal In case of an error the function returns FALSE, otherwise TRUE. Range validity The range limitations of the source coordinates and the calculated target coordinates are examined on the basis the geographical coordinates specified under the term "Range (Lon / Lat)" in the list "Defaults of the Coordinate Systems". The syntax and range examination can be switched off by the function setCoordArea(). With user-defined Coordinate Systems the range values are calculated automatically from the origin point of the respective Coordinate System. Notations The coordinates of the different Coordinate Systems are written with the notations specified under the term "Notation (E / N)" in the list "Defaults of the Coordinate Systems". As many as desired right-of-comma positions can be added. A specification of the notations can be found at the end of the list "Defaults of the Coordinate Systems". Standard Reference Systems The Reference Systems specified under the term "Standard RefSys" in the list "Defaults of the Coordinate Systems" are assigned to the Coordinate Systems, if in the parameters nRefSysQ or nRefSysZ a zero is passed. Special features using Reference Systems with Helmert Parameters: Forward and Backward Transformation: GeoDLL calculates Reference System Transitions with Helmert transformation parameters as Forward and Backward Transformations. With a Forward Transformation, starting from the source system, first the rotations and then the translations are performed. With a Backward Transformation, leading to the target system, in reverse order first the translations and then the rotations are calculated. Forward and Backward Transformations are executed each across the current dynamic Reference System WGS84. Calculating bidirectional coordinate transformations with Forward and Backward Transformations like in GeoDLL does not lead in minor deviations, that occur in many GIS. Small and large rotation angles: Normally, geodesic software only supports very small rotation angles when transforming with seven Helmert transformation parameters. In GeoDLL, the fast, simplified rotation matrix is resolved for small rotation angles up to 5 seconds. At larger angles, the slower, complete rotation matrix is resolved to maintain accuracy. In this way, both the high accuracy and the high calculation speed is guaranteed. Special features using Reference Systems with NTv2 grid files Download of NTv2 files: The commonly used NTv2 files can be download from the KilletSoft-Website or can be purchased from suppliers of geoservices. Combination prohibiting: NTv2 Reference Systems are identified by the suffix "NTv2" in the designation. When setting an NTv2 Reference System for the Source or Destination Coordinate System, on the other side must be set the equivalent Reference system of the associated NTv2 file. The combination of NTv2 Reference Systems with Helmert or Molodensky Reference Systems is not possible. Encrypted NTv2 files: To protect the rights of some authors that provide NTv2 files specifically for use with KilletSoft products, GeoDLL supports encrypted NTv2 files that can be download from the KilletSoft website. Polygonal Validity Scopes: The scope of a NTv2 file is by default defined by rectangular coordinate boxes. In order to be able to implement polygonal structures, e.g. such as national borders, the producer of a NTv2 file therein can specify a Polygonal Validity Scope. For this, outside of the poligonal validity located grid meshes are indicated by the exopolygonal entries -99/-99 in their shift or accuracy values. GeoDLL can check the grid meshes on exopolygonal entries and exclude hits from the calculation and comment them with an error message. The Polygonal Validity Check will be switched on or off using the function setntvpolyvalid(). Detailed information can be found in the help section "Polygonal Validity Scopes". Unlocking: This function is a component of the unlock requiring function group "Coordinate Transformations". It is unlocked for unrestricted use together with the other functions of the group by passing the unlock parameters, acquired from the software distribution company, trough the function setunlockcode(). Without unlocking only a few function calls for test purposes (shareware principle) are possible. Reference System Transitions with NTv2 grid files require an additional unlocking of the function group "NTv2 Transformations". |