[Proj] convert from Equidistant Cylindrical to Eckert I

[Norman Vine]

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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