Automated Java to Rust translation

Hello everyone,

I need to convert some equations for conversion of lat/long coordinates to UTM coordinates that were provided in Java to Rust (see geolocation - Java, convert lat/lon to UTM - Stack Overflow). That's not so hard, I know. However, these equations (there are four such equations) are ridiculous in their length. I have tried to manually convert them multiple times now and have run into problems, with things like incorrect bracket insertion, which results in errors. Given the redundancy in these equations, I do of course try to create intermediate variables to replace some of the duplicated terms. However, to be frank, this is seeming like an impossible task to do manually. Does anyone know of an automatic Java to Rust converter that might help. I saw a post from 2016 suggesting such a thing exists, but the link was dead.

As an example, here is one of the four equations (hold your breath for it!):

latitude = (north/6366197.724/0.9996+(1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2)-0.006739496742*Math.sin(north/6366197.724/0.9996)*Math.cos(north/6366197.724/0.9996)*(Math.atan(Math.cos(Math.atan(( Math.exp((Easting - 500000) / (0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2))))*(1-0.006739496742*Math.pow((Easting - 500000) / (0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2)))),2)/2*Math.pow(Math.cos(north/6366197.724/0.9996),2)/3))-Math.exp(-(Easting-500000)/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2))))*( 1 -  0.006739496742*Math.pow((Easting - 500000) / (0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2)))),2)/2*Math.pow(Math.cos(north/6366197.724/0.9996),2)/3)))/2/Math.cos((north-0.9996*6399593.625*(north/6366197.724/0.9996-0.006739496742*3/4*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.pow(0.006739496742*3/4,2)*5/3*(3*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996 )/2)+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/4-Math.pow(0.006739496742*3/4,3)*35/27*(5*(3*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/4+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/3))/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2))))*(1-0.006739496742*Math.pow((Easting-500000)/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2)))),2)/2*Math.pow(Math.cos(north/6366197.724/0.9996),2))+north/6366197.724/0.9996)))*Math.tan((north-0.9996*6399593.625*(north/6366197.724/0.9996 - 0.006739496742*3/4*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.pow(0.006739496742*3/4,2)*5/3*(3*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.sin(2*north/6366197.724/0.9996 )*Math.pow(Math.cos(north/6366197.724/0.9996),2))/4-Math.pow(0.006739496742*3/4,3)*35/27*(5*(3*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/4+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/3))/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2))))*(1-0.006739496742*Math.pow((Easting-500000)/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2)))),2)/2*Math.pow(Math.cos(north/6366197.724/0.9996),2))+north/6366197.724/0.9996))-north/6366197.724/0.9996)*3/2)*(Math.atan(Math.cos(Math.atan((Math.exp((Easting-500000)/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2))))*(1-0.006739496742*Math.pow((Easting-500000)/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2)))),2)/2*Math.pow(Math.cos(north/6366197.724/0.9996),2)/3))-Math.exp(-(Easting-500000)/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2))))*(1-0.006739496742*Math.pow((Easting-500000)/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2)))),2)/2*Math.pow(Math.cos(north/6366197.724/0.9996),2)/3)))/2/Math.cos((north-0.9996*6399593.625*(north/6366197.724/0.9996-0.006739496742*3/4*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.pow(0.006739496742*3/4,2)*5/3*(3*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/4-Math.pow(0.006739496742*3/4,3)*35/27*(5*(3*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/4+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/3))/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2))))*(1-0.006739496742*Math.pow((Easting-500000)/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2)))),2)/2*Math.pow(Math.cos(north/6366197.724/0.9996),2))+north/6366197.724/0.9996)))*Math.tan((north-0.9996*6399593.625*(north/6366197.724/0.9996-0.006739496742*3/4*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.pow(0.006739496742*3/4,2)*5/3*(3*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/4-Math.pow(0.006739496742*3/4,3)*35/27*(5*(3*(north/6366197.724/0.9996+Math.sin(2*north/6366197.724/0.9996)/2)+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/4+Math.sin(2*north/6366197.724/0.9996)*Math.pow(Math.cos(north/6366197.724/0.9996),2)*Math.pow(Math.cos(north/6366197.724/0.9996),2))/3))/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2))))*(1-0.006739496742*Math.pow((Easting-500000)/(0.9996*6399593.625/Math.sqrt((1+0.006739496742*Math.pow(Math.cos(north/6366197.724/0.9996),2)))),2)/2*Math.pow(Math.cos(north/6366197.724/0.9996),2))+north/6366197.724/0.9996))-north/6366197.724/0.9996))*180/Math.PI;
       

Doesn't the Rust "utm" crate already do that?
https://docs.rs/utm/0.1.4/utm/

1 Like

Well that could work! I'll need to look into that now. Thanks for drawing my attention to this crate.

1 Like

Looks like the crate only provides the one direction of conversion (lat/long -> UTM) and not the other direction (UTM -> lat/long).

I managed to do this by hand without too much trouble: Rust Playground

Here's the process I used:

  • Put the java expression in a function and run rustfmt
  • Define a local Math type to provide the methods used in the Java expression
  • Turn off some style warnings
  • Add .0 to literals, wherever the compiler complained about int/float conflicts
  • Replace Math.PI with std::f64::consts::PI

This assumes that Rust and Java have the same precedence for arithmetic operators. If that's not true, this gets a lot more complicated.

3 Likes

But looks like the GeoMorph crate will do!

Now that is an interesting solution! I never thought of that. Seems a bit inelegant having to create a Math struct, but the pragmatist in me really likes this approach. Thanks.

1 Like

Another approach would be a simple find/replace Math.sin(...) with f64::sin(...), etc. But I was working directly on the playground, which doesn't have a replace feature (at least on my browser).

1 Like

Vi commands work fine in the playground.

:s/Math[.]/f64::/g
:s/pow/powf/g
:s/\b([\d.]+)/$1_f64/g
:s/f64::PI/std::f64::consts::PI

Instead of adding .0, which requires recognizing the difference between an integer and a floating-point literal, I just added _f64 to the end of all numeric literals.

3 Likes

I had never explored the editor options before; switching it to vim mode will help immensely.

I dud something similar that when converting some Javascript geocoordinate handling methods to Rust. Writing Javascript in Rust ... almost

2 Likes

I should perhaps note that those commands will not actually work in Vim proper: the regex syntax is not quite right. But they do work in the playground (and almost all other Vim features that I usually use work acceptably well too)

1 Like

I also like this approach, and wanted to an advantage that just occurred to me. Writing with a Math struct in this way makes it abundantly clear that they code is from a different language, which actually improves the clarity by explaining went it's so horrible. It's because it's from horrible Java code. And then the reader can skip over it if they're confident that the original Java code was ugly but bug free. And the closer the rust code is to the Java code, the easier it will be to verify that no new bugs were introduced in translation.

Yes. I like the approach because I feel I feel it reduces the risk of making some silly error in translation to have the Rust code look as similar as the original language version.

I'm not sure if it's appropriate in all situations though. Perhaps sometimes the original code is so impenetrable that it worth investing the time to make it's working clearer.

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