Morphometry: Slope and Aspect strange values

User Forum
2012-04-05
2012-07-20
  • Mihai Niculita

    Mihai Niculita - 2012-04-05

    Hi,

    I found that in SAGA 2.0.7 annd 2.0.8 function Terrain Analysis - Morphometry
    / Slope, Aspect, Curvature has a problem. It computes the variables, but in
    Slope and Aspect in Object Properties Options, list at General / Z-Factor the
    value 57.295779513082323. From what I know this Z-Factor can be used for Z
    unit conversion, in this case influencing the use of Slope and Aspect for
    other functions (for Reclassification, the entire grid has the value 1, while
    when doing Grid Calculator calculations the results are correct).

    Has someone any idea about that problem. I have looked at the code but I am
    not very good in C programming to say where can be the problem.

    Mihai

     
  • Johan Van de Wauw

    180/pi =57.29...

    Values are calculated in radians, but shown in decimal degrees.

     
  • Mihai Niculita

    Mihai Niculita - 2012-04-05

    I agree, but this influence the usability of the grids. I don't remember to
    have the same type of problems in SAGA 2.0.6.

    Mihai

     
  • Volker Wichmann

    Volker Wichmann - 2012-04-06

    Hi Mihai,

    slope, aspect, shading ... have always been calculated in radians and used a
    z-factor to convert to decimal degree for display purposes. Actually all SAGA
    modules that require such a dataset as input expect it to be in radians - so
    there should be no usability problems within SAGA. It's just that you have to
    multiply your grids with the z-factor in case you switch to another program
    which can not handle slope etc. in radians.

    Volker

     

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