[GRASS-user] How to find out an angle between to points on the map (for r.plane, r.lake)

[Dylan Beaudette]

On Sat, Mar 1, 2008 at 7:18 AM, Michael Barton <michael.barton at asu.edu> wrote:
>
>
>  On Mar 1, 2008, at 1:47 AM, Martin Landa wrote:
>
>  > Micheal,
>  >
>  > 2008/3/1, Michael Barton <michael.barton at asu.edu>:
>  >>> 2008/2/29, Dylan Beaudette <dylan.beaudette at gmail.com>:
>  >>> [snip]
>  >>>> Thanks for the update. I don't regularly use either of the GUI and
>  >>>> did
>  >>>>  not know about this feature. Does the patch that I submitted
>  >>>> interfere
>  >>>>  with this functionality? I think that it would be useful to have
>  >>>> this
>  >>>>  functionality in the old style monitors as well.
>  >>>
>  >>> d.measure is not used in wxGUI. Display windows are not
>  >>> registered as
>  >>> GRASS displays (d.mon -L) [TODO, not sure how to implemented], I
>  >>> think
>  >>> it would be good to use d.measure or something like g.measure in
>  >>> wxGUI
>  >>> too instead of using Python-based function for distance calculation
>  >>> (at least it would make sense for LL projections)? Please correct me
>  >>> if I am wrong.
>  >>
>  > Michael,
>  >> What's wrong with the Python one?
>  >
>  > duplication of the code, and in this particular case ignoring geodetic
>  > distance for LL projections.
>
>  Well, my understanding of the direction of GRASS is that by v7, we'll
>  lose all the interactive xterm-specific d.* modules. Interactive use
>  will all be shifted to whatever GUI we design, rather than being hard-
>  coded into a module. Simple, interactive measurement between 2 points
>  on a display screen seems to me something to be handled by a GUI.

I agree completely-- despite the fact that I prefer the d.* commands
for now, an integrated approach would be nice. That said, it would be
nice to retain something like the current d.* commands. Nothing is
faster when working with a couple raster/vector files.

>  d.measure will go away OR change to a module in which you enter a
>  start and end point and it returns the distance between the points.
>  In the latter case, it could then be 'plugged into' a GUI as a
>  function to calculate distance between points interactively 'grabbed'
>  by the GUI.

Sure. Until then it would be nice to have something that works, and
provides some missing functionality.

>  Ignoring geodetic distance for LL projections is simply ignorance (on
>  my part here) of the equations needed to do it. It's easy to
>  determine if a location is LL. In that case, it should calculate
>  geodetic distance rather than (or perhaps in addition to) displaying
>  distance in map units. Just need to have the functions to do this
>  added to the measurement methods.
>
>  Michael
>

I see quite a bit of disconnect between the GUI development and core
GRASS development (I am not helping this either). It would be a good
idea to spend some careful thought, with lots of input from everyone
involved to nail down the general plan for GRASS 7. I can see a lot of
potential for hurt feelings (= lost developers) if a slow and methodic
approach is not taken.

Cheers,

Dylan