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Re: [O] link abbreviation with multiple params, e. g. for geo locations


From: Michael Brand
Subject: Re: [O] link abbreviation with multiple params, e. g. for geo locations
Date: Mon, 6 May 2013 20:42:54 +0200

On Mon, May 6, 2013 at 9:06 AM, Christian Moe <address@hidden> wrote:

> PS. If Org were to add a default geo: link type, I think it would make
> sense to keep the parameters to a minimum, i.e. just the latitude and
> longitude, without backend-dependent options such as Google Maps' "spn"
> parameter. Though I can see how it would be useful.

Good point, agreed. So what I am trying to do is less about a link
type "geo location" but more about possibly having several different
visualizations of one single geo location.

> When link abbreviations do not suffice, you can always write a link
> definition in Lisp and add it with org-add-link-type.

Thinking about this and my previous post I conclude that Org babel is
just perfect for my use case. Well, as a beginner of Org babel I am
not yet there completely and would like to ask for help on the source
block header:

--------------------------------------------
* Org babel function for Google Maps browser
  #+NAME: gmb
  #+HEADER: :var ty="m" spn=0.2
  #+HEADER: :var geo_var=(or (org-entry-get nil "geo") "4.56,7.89")
  #+BEGIN_SRC emacs-lisp :results silent
    (browse-url
     (concat "http://maps.google.ch/maps?t="; ty
             "&spn=" (number-to-string spn) "," (number-to-string spn)
             "&ll=" geo_var "&q=" geo_var))
  #+END_SRC
* example of a geo location, realistic to try out
  :PROPERTIES:
  :geo:      4.56,7.89
  :END:
  - call_gmb()
    - interactively (type C-c on "call_gmb") visualize the current geo
      location on Google Maps with a marker and as "map" in the
      browser
  - call_gmb(ty="k", spn=0.002)
    - visualize the same geo location on Google Maps with a marker, as
      "satellite image" and with a certain scale suitable for this
      specific geo location and view type
* another geo location
  :PROPERTIES:
  :geo:      4.44,5.55
  :END:
  - call_gmb(ty="p")
    - visualize another geo location as "terrain"
--------------------------------------------

The issue is that org-entry-get returns nil instead of the value of
the item property :geo:, therefore my "demo workaround" with the "or"
to show the principle of "gmb". How to resolve this properly?

Isn't there something like "#+HEADER: :var geo_var=:geo:" to copy the
value of the item property :geo: to the babel variable unless
specified by the caller?

Not sure yet how to support export of such geo locations to a GPS
track... That would probably be "simply" all item properties :geo:
with the item's name and nothing else. Probably quite a boring
exercise of writing a new exporter backend for someone who would know
how to do it...

Btw. I re-found the Org mode mailing list thread
[2010-06-29 Tue] "Getting a Google Maps' map for an entry"
http://thread.gmane.org/gmane.emacs.orgmode/26797
by Julien Danjou, currently to be found at
http://julien.danjou.info/projects/emacs-packages#google-maps
It can also be used as a backend to visualize a geo location and
demonstrates the usage of the interesting Google Maps Static Maps API
that converts a Google Maps URL to an image:
https://developers.google.com/maps/documentation/staticmaps/#quick_example

Michael



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