[GRASS-user] Re: link to datasets from other locations?

Hamish hamish_b at yahoo.com
Thu Jul 2 03:07:21 EDT 2009

Tim wrote:
> >> So sharing data between locations is not really supported?
> > Not at all supported. (except for v.proj, r.proj, i.rectify)
> What about a command that lets users safely move a vector
> from one locagion into the other?

as above. this is on purpose to protect distinct map projections.

> > if you want to mix things you must use multiple mapsets from
> > the same location with @othermapset.
> But how to /display/ data from another location?

cp, mv, ln in the mapset if you really want and don't need to reproject.
'display' is no different to any other GIS function- you can either read
map data or you can't.

> Imagine a shared location with common data such as world
> borders or GSHHS. It would not be space efficient to import
> such large data into every new project.
> Rather sharing the common location when needed.

make it a common Mapset not a common Location. or within your
common location make a mapset called 'common' then symlink that around
to other Locations of Exactly the same projection settings.

(no warranty)

2c POV:
*every* single GIS I have seen which does on-the-fly reprojection has had
major problems which can present itself in a way which is not obvious
to the user (typically due to mixed datums). Then the user happily goes
along doing their work, publishing their reports, only sometimes
realizing that something has misaligned internally. Or ugly non-solutions
like rubber sheet dragging to visually correct the misalignment without
considering the real cause become taught as the de facto method in the
workflow. (easier than teaching about ellipsoids and datum math)

I admit it's not the same as theoretically it could be done correctly,
but I sort of class it with the common request for scalebars or 1:xx,xxx
map scale for lat/lon cartography. It sounds like a good idea, and lots
of other software give the users what they demand there, but that doesn't
mean it's valid or a good idea. For map projections it is not invalid,
just really really hard to get right (probably because "right" is often
a very subjective answer in geodetics).



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