[Qgis-developer] QGIS 3.0: Plans to support librttopo?

[Nyall Dawson]

On 7 March 2017 at 15:37, Mark Johnson <mj10777 at googlemail.com> wrote:
>>> Everything you need should already be encapsulated in QgsRenderContext
>>> (and the QgsMapToPixel member).
>
> For everything but degrees it is.
> But in the case of degrees is is not
> - there the (incorrect) assumption is being made that the world is flat
> The value being used for DEGREE_TO_METER 111319.49079327358
> - is only valid on the Equator
> In my area a degree is around 66666,666666667 meters
> - and this is the value needed
>
>>> This shouldn't be implemented using an external dependency
> I understand the reluctance to adding a further dependency, but GEOS is also
> used
> - and librttopo is an extension of GEOS
>
> Unfortunately there are not many degree based functions that allows the
> combination with a distance as meters.

I'm confused - what is missing? You have the extent, map scale, and
source and destination crs with their corresponding map units. What
more is needed?

Nyall