Length of a deg in metres

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Length of a deg in metres

Nicolas Cadieux
Hi,

I am writing to python code to calculate the length (in metres) of a
degree of longitude at a certain degree of latitude.  I would like to
take various ellipsoid in mind (WGS84, GRS80, Clarke 1866...).  The goal
is to find the right scale (or z factor) when making slope or shade
raster models when x and y are in long/lat and z in feet or meters.  Can
someone point me in the right direction to do this in using Proj?  Is
Proj the best option for this?

Thanks,

Nicolas

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Re: Length of a deg in metres

Saulteau Don
I'm certain someone is going to be more knowledgeable than I, but I do sometimes go back to this answer at GIS.se to get some insight.


The user shares some formulas for obtaining both the scale and z-factor.

For other ellipsoids (the answer uses WGS84) it's a matter of determining the length of one degree (longitude) at the equator in metres. For WGS84 it's 111320m for example.
The longitude is from the center of the area of interest.


Donovan


On Thu, Nov 8, 2018 at 8:22 AM Nicolas Cadieux <[hidden email]> wrote:
Hi,

I am writing to python code to calculate the length (in metres) of a
degree of longitude at a certain degree of latitude.  I would like to
take various ellipsoid in mind (WGS84, GRS80, Clarke 1866...).  The goal
is to find the right scale (or z factor) when making slope or shade
raster models when x and y are in long/lat and z in feet or meters.  Can
someone point me in the right direction to do this in using Proj?  Is
Proj the best option for this?

Thanks,

Nicolas

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[hidden email]
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Re: Length of a deg in metres

Charles Karney
In reply to this post by Nicolas Cadieux
Dunno about getting the result from proj.  The formula you want is given
in

https://en.wikipedia.org/wiki/Longitude#Length_of_a_degree_of_longitude

This includes the ellipsoidal correction.

On 11/8/18 10:18 AM, Nicolas Cadieux wrote:

> Hi,
>
> I am writing to python code to calculate the length (in metres) of a
> degree of longitude at a certain degree of latitude.  I would like to
> take various ellipsoid in mind (WGS84, GRS80, Clarke 1866...).  The goal
> is to find the right scale (or z factor) when making slope or shade
> raster models when x and y are in long/lat and z in feet or meters.  Can
> someone point me in the right direction to do this in using Proj?  Is
> Proj the best option for this?
>
> Thanks,
>
> Nicolas
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
>
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Re: Length of a deg in metres

Luí­s Moreira de Sousa
In reply to this post by Nicolas Cadieux
Hi Nicolas,

PROJ itself relies on the GeographicLib package [0] for the computation of geodesics and rhumb lines. Since you are programming in Python, the easiest option is to use directly the GeographicLib port to Python [1].

Regards.

[0] https://geographiclib.sourceforge.io/
[1] https://pypi.org/project/geographiclib/

--
Luís Moreira de Sousa
Email: [hidden email]
RingID: ring:7ca91d83f4f9dec82fec9f1144b8e5c1ef2a110c
URL: https://ldesousa.github.io

Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Thursday, November 8, 2018 4:18 PM, Nicolas Cadieux <[hidden email]> wrote:

> Hi,
>
> I am writing to python code to calculate the length (in metres) of a
> degree of longitude at a certain degree of latitude.  I would like to
> take various ellipsoid in mind (WGS84, GRS80, Clarke 1866...).  The goal
> is to find the right scale (or z factor) when making slope or shade
> raster models when x and y are in long/lat and z in feet or meters.  Can
> someone point me in the right direction to do this in using Proj?  Is
> Proj the best option for this?
>
> Thanks,
>
> Nicolas
>
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj


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Re: Length of a deg in metres

Nicolas Cadieux
Hi,
Thanks everyone for pointing me in useful directions.
Nicolas

> Le 9 nov. 2018 à 05:30, Luí­s Moreira de Sousa <[hidden email]> a écrit :
>
> Hi Nicolas,
>
> PROJ itself relies on the GeographicLib package [0] for the computation of geodesics and rhumb lines. Since you are programming in Python, the easiest option is to use directly the GeographicLib port to Python [1].
>
> Regards.
>
> [0] https://geographiclib.sourceforge.io/
> [1] https://pypi.org/project/geographiclib/
>
> --
> Luís Moreira de Sousa
> Email: [hidden email]
> RingID: ring:7ca91d83f4f9dec82fec9f1144b8e5c1ef2a110c
> URL: https://ldesousa.github.io
>
> Sent with ProtonMail Secure Email.
>
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
>> On Thursday, November 8, 2018 4:18 PM, Nicolas Cadieux <[hidden email]> wrote:
>>
>> Hi,
>>
>> I am writing to python code to calculate the length (in metres) of a
>> degree of longitude at a certain degree of latitude.  I would like to
>> take various ellipsoid in mind (WGS84, GRS80, Clarke 1866...).  The goal
>> is to find the right scale (or z factor) when making slope or shade
>> raster models when x and y are in long/lat and z in feet or meters.  Can
>> someone point me in the right direction to do this in using Proj?  Is
>> Proj the best option for this?
>>
>> Thanks,
>>
>> Nicolas
>>
>> Proj mailing list
>> [hidden email]
>> http://lists.maptools.org/mailman/listinfo/proj
>
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
_______________________________________________
Proj mailing list
[hidden email]
http://lists.maptools.org/mailman/listinfo/proj