[gdal-dev] Spatial references and geometry operations

[Paul Harwood]

As a very general response, you probably need to differentiate between two
possible questions that you are asking, either:

1 Does the operation fail with an error, or
2 Is the result correct or meaningful?

I don't know about 1). My guess and experience is that, in most cases, it
won't fail.

However, I would make the case that most operations are undefined if the
system is making (possibly) unknown assumptions about the CRS. If you are
asking for the point at a distance along a line or a buffer then you are
implicitly or explicitly giving the system an input distance, so you are
making assumptions about the CRS of your input. If your assumptions do not
match the system's assumptions for the CRS, then the result will be wrong.
I would say that it is always better to make the definition of the CRS
explicit and then the result is defined.



On Fri, 29 Sept 2023 at 03:32, adamgutonski via gdal-dev <
gdal-dev at lists.osgeo.org> wrote:

> Hello,
>
> I am using geometry object functions like Buffer and Value.  I am
> wondering if and when it is necessary to assign a spatial reference to an
> ogr.Geometry before calling these functions?  For example if I want to get
> a point along the line using Value is the output affected by whether or not
> the ogr line geometry has an assigned spatial reference?  Is there a way to
> tell what geometry functions are affected by this or not?
>
> Thanks,
> Adam Gutonski
>
> Sent with Proton Mail <https://proton.me/> secure email.
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