Re: st: 3D Surface Plot Interpolation

[Sergiy Radyakin <serjradyakin@gmail.com>]

Hi Joe,

Recently Stata added support for contour plots, I assume there is a
similar task there, to smooth the color transitions. Check them out
for bits and pieces. Perhaps you don't need a 3D plot after all, and
can simply produce a contour plot?

That said, smoothing and plotting are two separate tasks, though some
of the Stata commands like lowess do both.

for smoothing check Kolenikov's message:
http://www.stata.com/statalist/archive/2012-01/msg00355.html

Akima's algorithm is here:
http://dl.acm.org/citation.cfm?doid=79505.79510
the article seems to require a purchase, but the code was available
for download (Fortran).

After smoothing is done in Stata, plotting can be done with either the
user-written command you quoted, or by means of exporting to e.g.
Excel, which supports surface plots.


Best, Sergiy




On Wed, Jul 24, 2013 at 10:17 AM, Joe Canner <jcanner1@jhmi.edu> wrote:
> At the recent Stata Conference "wishes and grumbles" session, several of us expressed interest in 3D Surface plots.  StataCorp did not give much reason for optimism in this area.  There is currently a user-written module "surface" which does an OK job of 3D surface plots, but does not have a feature for interpolating and smoothing.
>
> In SAS, for example, there is PROC G3GRID, which provides a data set with interpolated/smoothed points which can then be plotted with PROC G3D.  G3GRID uses, among other methods, an interpolation method by Akima (1978) which involves forming triangles with existing (x,y) points, fitting a quintic bivariate polynomial for the three vertices of the triangle, and using the resulting model to fill in additional interpolated points.
>
> There is a set of Fortran subroutines for this algorithm and I would like to try my hand at converting them to Mata, but before I spend a lot of time doing that, is anybody aware of existing Stata functions or commands (user-written or native) that are available for this?
>
> Thanks,
> Joe Canner
> Johns Hopkins University School of Medicine
> Department of Surgery
>
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