[mapserver-dev] Request for review/comments on RFC 85 (Contour Layer Rendering)

[thomas bonfort]

On Thu, Sep 20, 2012 at 11:56 PM, Frank Warmerdam <warmerdam at pobox.com> wrote:
> On Thu, Sep 20, 2012 at 11:21 AM, thomas bonfort
> <thomas.bonfort at gmail.com> wrote:
>> Frank,
>> By that do you mean that the generated vector features will all be
>> roughly one pixel long, or that the points inside a generated line
>> will be roughly one pixel away from each other?
>
> Thomas,
>
> I mean the latter - each line segment in the line string will be
> roughly one pixel long.
>
>> In the first case, this would be a major problem, as it will be
>> impossible to generate labels that follow a contour line. In the
>> second case, the vector renderers won't slow down noticeably on line
>> data that is sampled like this.
>
> Good, no problem for rendering labels.  I'm a bit surprised
> that this density would not some problems for speed.

It is of course slower than if you had N times less vertices to treat,
however my gut feeling is that the overall performance will be very
far from N times slower. Given that the vertice resolution is equal or
similar to the pixel resolution/density, I'd say that the proposed
1-pixel resolution is the ideal output from the contour generator. You
could always transparently couple that with Daniel's proposed
smoothing/simplification methods if the need arises.

--
thomas

>
>
>
> On Thu, Sep 20, 2012 at 11:30 AM, Stephen Woodbridge
> <woodbri at swoodbridge.com> wrote:
>> In the second case do the contour lines all become pixel stair steps? if
>> this is the case, I would thing some smooth of the line speed things up a
>> little and for labeling I would think it would generate smoother labels, but
>> maybe not.
>>
>> -Steve W
>
> Steve,
>
> The line segments will cross the pixels at a diagonal
> based on interpolation between neighbouring pixels so
> you don't get the vertical/horizontal stairstep effect but
> you may still be getting more location variation than
> is actually useful.
>
> Best regards,
> --
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Software Developer