[Qgis-user] Projections

Thu Oct 22 12:50:15 PDT 2020

 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 <charles at kartoza.com> 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 <fhuettmann at alaska.edu> 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 <mikemcgrady at hotmail.com> 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 <qgis-user-bounces at lists.osgeo.org> on behalf of Hernán De Angelis <variablestarlight at gmail.com>
Sent: Thursday, October 22, 2020 6:57 AM
To: qgis-user at lists.osgeo.org <qgis-user at lists.osgeo.org>
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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