Re: [guide-user] Plotting trails in Guide

Fraser Farrell May 11, 2001

>When creating a trail in Guide, I'd like to be able
>to place date labels near the tick marks.

You can do it with Guide's text label overlay but it's
clumsy. I do my labelling with an image editor too.


>Also, I've noticed an odd problem with trails. After
>creating a trail, if I zoom in on it, the trail becomes
>bent at a sharp angle.

I've seen this too. My guess is that exact positions are
calculated for each "step time", and then Guide simply draws
a straight line from step to step. Under some conditions the
line may fall outside your field of view. It would look
nicer with a spline routine to draw the line, but they take
much longer to compute, and then Guide has to keep track
[pun intended] of all the in-between bits.

Workaround: set the step size to something much smaller than
your tick interval. For example I do comet trails with a
daily tick but with a step size of 2 or 4 hours. Or in the
case of distant objects, a tick every 10 days and a daily
step size. Effectively this is what a spline fit does
anyway.

Of course you can exaggerate this problem by fiddling the
settings. Try Mars with a step size of 30 days...

>
>A suggestion for a future version of Guide: I'd like to
>be able to delete individual trails (and DSS images too).

I second that!


cheers,
Fraser Farrell