[Proj] convert from Equidistant Cylindrical to Eckert I

[Jose Gonçalves]

Hi
You can transform your image with the following command line:

gdalwarp -s_srs "+ellps=WGS84 +proj=eqd" -t_srs "+ellps=WGS84 +proj=eck1"
in.tif out.tif

The input image must be georeferenced in the equidistant cylindrical
projection, with units in meters. See page http://www.gdal.org/gdalwarp.html.
Other important options are -r, -te and -tr.
Regards
José Gonçalves


2016-05-24 23:16 GMT+01:00 Wang Leslie <wqyuwss at hotmail.com>:

> Hi Norman, Dann,
>
> Thanks for quick reply. It would be highly appreciated for one sample
> command on these tools to achieve my goal.
>
> Best Regards
> Leslie
>
> ________________________________________
> From: proj-bounces at lists.maptools.org <proj-bounces at lists.maptools.org>
> on behalf of Norman Vine <nhv at cape.com>
> Sent: Tuesday, May 24, 2016 7:20 AM
> To: PROJ.4 and general Projections Discussions
> Subject: Re: [Proj] convert from Equidistant Cylindrical to Eckert I
>
> Hello Leslie
>
> I suggest using http://www.gdal.org/gdalwarp.html todo this
>
> To avoid the speckling that Daan mentions you want to loop over the new
> image
> pixels and do the inverse projection to find the pixel value in the
> original image
>
> gdalwarp takes care of this for you and is built on top of the proj library
>
> Norman
>
> > On May 24, 2016, at 3:05 AM, strebe at aol.com wrote:
> >
> > Hello Leslie.
> >
> > Your procedure will work. The results will be heavily aliased, which
> will look like speckling. Some values of (x₁, y₁) will be empty unless the
> destination map is considerably smaller than the source image.
> >
> > Regards,
> > — daan Strebe
> >
> >
> >
> > -----Original Message-----
> > From: Wang Leslie <wqyuwss at hotmail.com>
> > To: proj <proj at lists.maptools.org>
> > Sent: Mon, May 23, 2016 7:37 am
> > Subject: [Proj] convert from Equidistant Cylindrical to Eckert I
> >
> > Dear all,
> >
> > I'm new to this tool, and hope to get some advise here.
> >
> > I'm thinking to use your tool to convert a map picture which is based on
> Equidistant Cylindrical, to another picture based on Eckert I. Since both
> of them are 2 dimension only (x,y), what I'm gonna to do is:
> >  - Use proj command to calculate the new mapped coordinate (x1, y1)
> >  - Set new pixel value at (x1, y1) using original pixel value (x,y)
> >  - loop for all pixel at original Equidistant Cylindrical picture
> >
> > So can you please help me confirm if one idea can work or not? If yes,
> what should command line look like? Thanks.
> >
> > Best Regards
> > Leslie Qi Wang
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