Show the last course

[hem0773]

Show the last course or direction in the view! ?

lends the cold search

[TheSkorm]

@darksidelemm thoughts?

[darksidelemm]

What would probably be most useful is somehow showing a 'dead reckoning' track from the last sonde position, down to where that intersects with ground level. By read reckoning i just mean linear extrapolation based on the last known sonde position, heading, and descent rate. This could be shown with some other styling compared to the regular tawhiri prediction.

Issues with this are:

• We need to know what 'ground level' is. We could either keep a record of the last tawhiri prediction altitude (which will be based on ruaumoko data), or we have to query ruaumoko directly.
• We'd need to decide at what point to calculate/show these kinds of dead reckoning tracks. This would probably need to be based upon some height above ground level as well, so again, we need to know what ground level is. I would suggest that this is only shown if the last position of the sonde was <500m AGL. Higher than this and other wind layer effects will mean the tawhiri prediction would be more accurate.

Using the ground level data from the prediction is probably the best approach here. There will be cases where it will be inaccurate (mountainous terrain), but it's probably 'good enough' for our purposes.