[PROJ] PROJ7 in JavaScript

[Richard Greenwood]

Proj 6 and 7 don't really add any new functionality. Proj does forward in
inverse projections and it does datum transformations with 3 & 7 parameters
transforms and grid shift transforms. Proj4js supports most of the commonly
used projections and the 3 & 4 param datum transforms. It doesn't support
grid shift transforms and grid shift transforms are what are "heavy" in
terms of the size of the required data. I thought a lot about adding grid
shift support and considered a server-side option like Javier mentions, but
it's a lot of moving parts for pretty limited use cases. Like how many web
mapping apps need the precision of a grid shift transform? And for those
that do, how do you build a generic enough mechanism to cover the
variations in scale, platform, online/offline, etc.?

Bringing the proj4js code more inline with Proj 7 sounds like a nice goal.
It was never really even in sync with Proj4, it was just cobbled together
enough to work, not to maintain.

Web assembly sounds cool if you're thinking in a web browser context only
but modern JavaScript is often trying to support browsers and Node,
which web assembly would not do, or at least not in my very limited
knowledge of web assembly.

Rich


On Fri, Oct 2, 2020 at 7:58 AM Howard Butler <howard at hobu.co> wrote:

>
>
> On Oct 1, 2020, at 3:58 PM, Javier Jimenez Shaw <j1 at jimenezshaw.com>
> wrote:
>
> Hi
>
> As far as I know, there is no JavaScript version PROJ6 or 7. The last is
> https://github.com/proj4js/proj4js based on PROJ4. Am I right?
>
> Is there any plan to have anything like proj7js? Even more, does it make
> sense?
>
>
> Not as far as I know. Maybe you could put something forward. I think the
> path to explore is compilation of PROJ to WebAssembly and then build
> JavaScript wrappers over that. The SQLite database makes it a bit more
> challenging, but there are implementations of SQLite on WebAssembly too.
>
> Don't hand roll a port.
>
> Somebody mentioned that PROJ6 was too heavy for a web page, and making
> constant requests to a server was not feasible (when the user moves the
> mouse over a map and the coordinates are updated instantly, for instance).
>
>
> The download of proj.db would be a bit of a hit, but it's conveniently
> cacheable per-page and doesn't change after it is fetched. Once it is
> local, a JavaScript PROJ implementation based on WebAssembly could use it
> do its queries just as C-language PROJ does today.
>
> Howard
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>


-- 
Richard W. Greenwood, PLS
www.greenwoodmap.com
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