[Qgis-user] Projections

John Helly hellyj at ucsd.edu
Thu Oct 22 13:17:58 PDT 2020 

Aloha.
You might want to consider simply using Great Circle distances and then
refining that if you need something better.
J.

On 10/22/20 12:50, Peter Borissow wrote:
> 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
> <mailto: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
>     <https://urldefense.com/v3/__https://www.researchgate.net/publication/12122402_Migration_Along_Orthodromic_Sun_Compass_Routes_by_Arctic_Birds__;!!Mih3wA!RyMpbAKaWAmYgznMW5fozhrNvNNW3iiURGcMTtYC4nYC8sSDMHP23tv29mkBPrc$>
>
>     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 etc
>     no 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 <mailto: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 59
>         A-3500 Krems
>         Austria
>
>         ------------------------------------------------------------------------
>         *From:* Qgis-user <qgis-user-bounces at lists.osgeo.org
>         <mailto:qgis-user-bounces at lists.osgeo.org>> on behalf of
>         Hernán De Angelis <variablestarlight at gmail.com
>         <mailto:variablestarlight at gmail.com>>
>         *Sent:* Thursday, October 22, 2020 6:57 AM
>         *To:* qgis-user at lists.osgeo.org
>         <mailto:qgis-user at lists.osgeo.org> <qgis-user at lists.osgeo.org
>         <mailto: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 59
>>         A-3500 Krems
>>         Austria
>>
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-- 
John Helly, University of California, San Diego / San Diego Supercomputer Center / Scripps Institution of Oceanography / 760 840 8660 mobile / http://www.sdsc.edu/~hellyj
ORCID ID: orcid.org/0000-0002-3779-0603

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