I agree with Hernán, that you are probably better off using ellipsoidal
(geodetic) distances rather than projected distances for such large tracks.
Of course, you can use whatever projection you want to RENDER the routes. For
example you can use a conic projection to render the bird tracks or a
orthographic map projection. It all depends on what message you are trying to
convey to your audience.
On Thursday, October 22, 2020, 3:14:34 PM EDT, Charles Dixon-Paver
<[email protected]> wrote:
Pardon my ignorance, but my brain is burning a bit with this topic... Is there
a particular reason nobody is suggesting the utilisation of an equidistant
projection? I thought this was what they are optimised for. Albers conic equal
area is for the preservation of area, not distance as far as I'm aware.
I know pretty much nothing of Two Point Equidistant projections, but
considering the field of interest is migration I feel like this is probably the
most accurate method (depending on implementation)? I would think an Azimuthal
Equidistant projection centered on the area of interest would be more accurate
than albers at least... And if the maps look way too funny then use something
like the equidistant conic?
This is pure conjecture on my part, so I'd appreciate the correction if I'm
missing the plot...
On Thu, 22 Oct 2020 at 19:35, Falk Huettmann <[email protected]> wrote:
Hi there, Mike et al,
thanks,but if you check up with Thomas Alerstam from Sweden - as a bird
tracking migration person you really ought to know those things and his entire
books/papers -there is sufficient literature on the topic for years re.
projections, e.g. this one for starters.
https://www.researchgate.net/publication/12122402_Migration_Along_Orthodromic_Sun_Compass_Routes_by_Arctic_Birds
Some others are found with the navigation sciences, with sea turtle math work
(former Ram Myers) and then rocket and missile targeting of course.It's usually
not written though by geography or GIS experts. The Google Earth maps boldly
ignore the projection issue (as they are just a shiny commercial PR tool).
Overall, for birds these days, the public resource question should sit on
CONSERVATION and sustainable management,not ivory-tower questions. The latter
have been done for centuries without relevant outcome and progress.Yes, the
earth is round and an optimal route exist, but now what ? Birds know and used
that for millennia and their presences show it no other.. Data exist to that
degree.Other problems are more relevant these days.
A nice question why after 100 years of research on bird migration, state-funded
with $Mio's, and with MPI and Movebank, ICARUS etcno readily available solution
or answer exist in R or GIS etc.
That's my opinion and answer on your question. Feel free to follow up as needed.
Best regards Falk Huettmann PhD, Professor Uni of Alaska Fairbanks
On Wed, Oct 21, 2020 at 11:53 PM MIKE MCGRADY <[email protected]> wrote:
As far as I can recall, few studies of long-distance migratory species state
what projections are used. Is there any published study of the effect of
projections on analyses of animal movement?
M
M. J. McGrady Am Rosenhugel 59A-3500 KremsAustria
From: Qgis-user <[email protected]> on behalf of Hernán De
Angelis <[email protected]>
Sent: Thursday, October 22, 2020 6:57 AM
To: [email protected] <[email protected]>
Subject: Re: [Qgis-user] Projections
Mike
For measuring the kind of distances you are mentioning I would suggest using
ellipsoidal (geodetic) distances rather than projected distances. This is
because projected distances can become very inaccurate over large regions
(depending on the particular projection of course).
If measuring areas is important consider an equal area projection, like Albers
for example, not a conformal one like Lambert.
Hope this helps.
/H.
On 2020-10-22 07:43, MIKE MCGRADY wrote:
I have data on tracked migratory birds, and want accurate measures of distance
travelled during migration and areas of summering and wintering ranges. These
birds are summering in central Asia (mostly Kazakhstan and southern Russia),
and wintering in Arabia. Any advice on which projection to use? My guess is
Lambert conformal conic. I'd really like to avoid using different projections
for different phases of the birds' annual cycle, unless absolutely necessary.
M. J. McGrady Am Rosenhugel 59A-3500 KremsAustria
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