# Generalities

### Presentation

Photogrammetry is often accompagned with a georeferencement (direct or indirect). The geographic position of targets or images is usually given in geographic system such WGS84 or RGF93 (France). To work with this coordinates in MicMac, yo have to transform it in a euclidian system. Best way is to work in a Local frame (RTL) define by the coordinates of one point of the field.

### How to Use?

Two way to transform coordinates :

For both case, you have to use the same syntax :

initial_coordinate_system@final_coordinate_system

For example, if you want to transform geographic to cartesian, you should use :

DegreeWGS84@GeoC

# Implemented systems

### Polynomial

14.5.2 XML codage 14.5.2.1 Generalities { speci�cation in �le ParamChantierPhotogram.xml { the class SystemeCoord contains the data necessary to create a C++ object cSysCoord { a SystemeCoord is made of several BasicSystemeCoord (one in the simplest case); { the �rst BasicSystemeCoord de�nes the coordinate system, the possible following BasicSystemeCoord are arguments used to de�ne this system; A BasicSystemeCoord is made from : { a TypeCoord �eld , of type eTypeCoord; { auxiliary vectors of values : AuxR for doubles, AuxI for integers, AuxStr for strings, AuxRUnite for unities ; the number and semantic of these datas is varying according to the TypeCoord; { the optionary boolean value ByFile, meaning that the system is de�ned in an exterior �le; The enumerated possible values of a eTypeCoord are : { eTC WGS84; { eTC GeoCentr { eTC RTL { eTC Polyn { eTC Unknown Obviously, the set of possible values may grow in the future. 14.5.2.2 Geocentric A geocentric coordinate system, de�ned by eTC GeoCentr, requires no argument. 14.5.2.3 eTC WGS84 A WGS84 coordinate system, de�ned by eTC WGS84, requires no argument. 14.5.2.4 Exterior �le coordinate system It is often convenient to de�ne once a coordinate system in a �le, and to use it several times. In this case, for the XML-structure : { ByFile must be true ; { there must exist one AuxStr containing the name of the �le, this �le must contain a SystemeCoord

{ the TypeCoord being redundant must, or be equal to eTC Unknown or be equal to the value speci�ed in the �le (for coherence reason, as they are redundant). 14.6. TOOLS FOR PROCESSING TRAJECTORY AND COORDINATE SYSTEMS 213 14.5.2.5 Locally tangent repair A locally tangent repair, speci�ed by eTC RTL must contain : { three values AuxR containing the origin of the repair; { optional AuxRUnite values, specifying the angular unities in which the origin is given; If the �rst BasicSystemeCoord of a SystemeCoord is of type eTC RTL , it must contain a second BasicSystemeCoord indicating the coordinate system in which the origin is given. 14.5.2.6 Polynomial coordinate system Sometimes it is convenient to use a coordinate system, that is known by a set of example, the analytic formula being unknown. In this case, it can be stored as a polynomial tranformation between a known coordinate system and the unknown system. A polynomial coordinate system, speci�ed by eTC Polyn, is stored this way in XML format : { the �rst BasicSystemeCoord stores the polynomial transformation, and the second store the known coordinate system; { it contains three polynoms Px, Py,Pz for direct mapping and three polynoms for inverts mapping; this polynoms works on "normalized" coordinates, the normalization parameters are stored in AuxR after the polynom coe�cient; { the degree of the polynom are speci�ed by AuxI (there are 9 AuxI)