[Proj] convert from Equidistant Cylindrical to Eckert I

[Wang Leslie]

Hi Jose,


Thanks for the quick reply.


What do you mean "be geo-referenced"? What I'm thinking is to use these tools to convert a 360 panorama picture, such as https://upload.wikimedia.org/wikipedia/commons/3/35/Space_Needle_360_Panorama.jpg, which is an equidistant cylindrical projection, to other type of projection, which keeps same quality but with smaller size. Thus I can save some storage spaces. In this case, these 360 picture doesn't have any geo-referenced data. Can I still use these tools?


[https://upload.wikimedia.org/wikipedia/commons/3/35/Space_Needle_360_Panorama.jpg]


________________________________
From: proj-bounces at lists.maptools.org <proj-bounces at lists.maptools.org> on behalf of Jose Gonçalves <jagoncal at gmail.com>
Sent: Tuesday, May 24, 2016 11:03 PM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] convert from Equidistant Cylindrical to Eckert I

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.
GDAL: gdalwarp<http://www.gdal.org/gdalwarp.html>
www.gdal.org
image reprojection and warping utility. SYNOPSIS. Usage: gdalwarp [--help-general] [--formats] [-s_srs srs_def] [-t_srs srs_def] [-to "NAME=VALUE"] [-order n | -tps ...



Regards
José Gonçalves


2016-05-24 23:16 GMT+01:00 Wang Leslie <wqyuwss at hotmail.com<mailto: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<mailto:proj-bounces at lists.maptools.org> <proj-bounces at lists.maptools.org<mailto:proj-bounces at lists.maptools.org>> on behalf of Norman Vine <nhv at cape.com<mailto: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<mailto: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 (x?, y?) 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<mailto:wqyuwss at hotmail.com>>
> To: proj <proj at lists.maptools.org<mailto: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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