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Cosme

Geographic depiction of error in FLightR

Question

Dear all,

 

I am trying to geographically illustrate the 95% Credible Intervals of the estimated positions along the track. My goal is to obtain a polygon defined as the "concave minimum polygon" of positions UCI and LCI, which indicate the upper and lower limits of the 95% credible intervals (or confidence intervals).

 

The depiction of this error is nicely illustrated by the lat/long plots, but I wanted to show them geographically explicit within a map. 

 

My problem is: the line defined by UCI crosses the line defined by LCI during first October. Interestingly, lines cross each other close to the Greenwhich Meridian. So I wonder if the CI limits are inverted when the bird travel through the Greenwhich Meridian, because the longitude changes from positive to negative, or vice-versa. I also wonder if the equinox may be involved in this.

 

In summary, UCI and LCI positions build up a polygon with the shape of a sandglass. How are the UCI and LCI positions calculated in FLightR?

 

Best whises,

Cosme


 

sandglass
 

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  Hi Cosme,

 I am not sure I can fully imagine what you are talking about, but expect you see some strange plotting around 0 meridian. This can definitely happen but it is likely not an error but incorrect assignment of Left and right CI while near 0 meridian. You can try to correct it by hand by swapping left and right CI for specific points. If it does not help, send me your result object and code by mail and I will have a look.

  Eldar

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Hi Eldar,

 

thank you very much. I have been correcting these points by hand, it is possible but very time-consuming if I want to pool together in the same map many different tracks.

 

Best wishes,

Cosme

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  You can try automating it. Let's say left is replaced with right for the cases when right crosses 0 meridian. 

You can do then something like

 Left_corrected<-Left
 Right_corrected<-Right
 Left_corrected[condition when right is not correct]<-Right
 Right_corrected[condition when right is not correct]<-Left

  Hope this helps.

    Eldar

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