dhis2-devs team mailing list archive

[Knut Staring <knutst@xxxxxxxxx>]

You are right, Calle, cannot use Lat/Lon - but pretty much any equal-area
projection should work, right?

Or is your concern that UTM is used? Would be strange to transform to UTM
rather than some, Cylindrical Equal-Area function, e.g. Gall-Peters.

But I will let Bjørn/Jan respond.

k

On Mon, Apr 25, 2016 at 3:28 PM, Calle Hedberg <calle.hedberg@xxxxxxxxx>
wrote:

> Knut,
>
> That makes no sense - nobody does area calculations on lat/long (i.e. the
> geographical graticule), you must first project the lat/long data into a
> suitable projection and then calculate areas.
>
> For smaller areas (e.g. small and medium-sized countries) you would
> typically use UTM (Transverse Mercator), but that is completely
> inappropriate for larger areas. Just think about it: on a standard global
> Mercator projection, Greenland looks twice as big as India - whereas the
> reality is that India has a 50% larger area than Greenland.
>
> Besides, if you do calculate areas using lat/long and decimal degrees, the
> "result" will be squared decimal degrees - which means nothing to anybody.
>
> Regards
> Calle
>
>
> On 25 April 2016 at 15:16, Knut Staring <knutst@xxxxxxxxx> wrote:
>
>> AFAIK all coordinates are lat/lon, so I suppose that also goes for the
>> area calculation.
>>
>> Knut
>>
>> On Mon, Apr 25, 2016 at 3:05 PM, Calle Hedberg <calle.hedberg@xxxxxxxxx>
>> wrote:
>>
>>> Lars,
>>>
>>> Thanks - it is downloading
>>>
>>> One initial question re GIS area calculations: what projection is used
>>> for the calculation?
>>>
>>> regards
>>> calle
>>>
>>> On 25 April 2016 at 14:53, Lars Helge Øverland <lars@xxxxxxxxx> wrote:
>>>
>>>>
>>>>
>>>> On Mon, Apr 25, 2016 at 2:39 PM, Calle Hedberg <calle.hedberg@xxxxxxxxx
>>>> > wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> Good stuff - will go through it in more detail, but please note that
>>>>> trying to download the 2.23 demo database gives an error (file not found).
>>>>>
>>>>> regards
>>>>> Calle
>>>>>
>>>>
>>>>
>>>> Right - fixed now.
>>>>
>>>>
>>>> --
>>>> Lars Helge Øverland
>>>> Lead developer, DHIS 2
>>>> University of Oslo
>>>> Skype: larshelgeoverland
>>>> http://www.dhis2.org <https://www.dhis2.org/>
>>>>
>>>>
>>>
>>>
>>> --
>>>
>>> *******************************************
>>>
>>> Calle Hedberg
>>>
>>> 46D Alma Road, 7700 Rosebank, SOUTH AFRICA
>>>
>>> Tel/fax (home): +27-21-685-6472
>>>
>>> Cell: +27-82-853-5352
>>>
>>> Iridium SatPhone: +8816-315-19119
>>>
>>> Email: calle.hedberg@xxxxxxxxx
>>>
>>> Skype: calle_hedberg
>>>
>>> *******************************************
>>>
>>>
>>> _______________________________________________
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>>>
>>
>>
>> --
>> Knut Staring
>> Dept. of Informatics, University of Oslo
>> Norway: +4791880522
>> Skype: knutstar
>> http://dhis2.org
>>
>
>
>
> --
>
> *******************************************
>
> Calle Hedberg
>
> 46D Alma Road, 7700 Rosebank, SOUTH AFRICA
>
> Tel/fax (home): +27-21-685-6472
>
> Cell: +27-82-853-5352
>
> Iridium SatPhone: +8816-315-19119
>
> Email: calle.hedberg@xxxxxxxxx
>
> Skype: calle_hedberg
>
> *******************************************
>
>


-- 
Knut Staring
Dept. of Informatics, University of Oslo
Norway: +4791880522
Skype: knutstar
http://dhis2.org