Coordinates Systems

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Generalities

Presentation

Photogrammetry is often accompagned with a georeference (direct or indirect). The geographic position of targets or images is usually given in geographic coordinate systems such as WGS84 or RGF93 (France). To work with this coordinates in MicMac, you have to transform them in an Euclidian system. The best way to do this is to work in a Local frame (RTL) defined from the coordinates of one (central) point of the field.

How to Use?

Two ways 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

XML codage

Sometimes it's more easier to define the systeme in a file to use it several times.

  • <SystemeCoord> : Define a system.
  • <BSC> : BasicSystemeCoord.
  • <TypeCoord> : Type of the coordinate (eTC_RTL,eTC_WGS84,etc...).
  • <AuxR> : for a double.
  • <AuxI> : for an integer.
  • <AuxStr> : for a string.
  • <AuxRUnite> : for unities.

Exemple :

<SystemeCoord>
   <BSC>
       <TypeCoord>eTC_RTL</TypeCoord>
          <AuxR>4320361.093</AuxR> #Center or RTL
          <AuxR>-98032.083</AuxR>
          <AuxR>4675380.773</AuxR>
   </BSC>
   <BSC>
      <TypeCoord>eTC_GeoCentr</TypeCoord> #Coordinate system of the center
   </BSC>
</SystemeCoord>

Implemented systems

Geocentric cartesian

  • Directly on MicMac commands : GeoC.
  • In file : eTC_GeoCentr.

WGS84 geographic

  • Directly on MicMac commands : WGS84, or DegreeWGS84
  • In file : eTC_WGS84.

RTL planes

This system creates a local system that is a plane tangent to the ellipsoid at the given center point. It is not recommended to use such a system for a large area. For this system, you need to define it on a xml file with this structure :

<SystemeCoord>
   <BSC>
       <TypeCoord>eTC_RTL</TypeCoord>
          <AuxR>4320361.093</AuxR> #Center or RTL
          <AuxR>-98032.083</AuxR>
          <AuxR>4675380.773</AuxR>
   </BSC>
   <BSC>
      <TypeCoord>eTC_GeoCentr</TypeCoord> #Coordinate system of the center
   </BSC>
</SystemeCoord>

Polynomial

To do