add us survey foot

[bartvde]

Coordinate systems based on the US Survey Foot are failing in OL 3.2.1. epsg.io uses the abbreviation 'us-ft'. The US Survey Foot is defined as 1200/3937 meters. It is widely used in US State Plane Coordinate Systems. I believe two additions are required in prij/proj.js:
ol.proj.Units.USFEET: 'us-ft',
and
ol.proj.METERS_PER_UNIT[ol.proj.Units.USFEET] = 1200/3937;
but I'm not user if "USFEET" follows your naming convention.

[ahocevar]

See https://groups.google.com/d/msgid/ol3-dev/CAHBySPaEfQpSishO2p0xL_255O6aF6K8-328sEz3C0SB%2BuzddQ%40mail.gmail.com for the original thread.

[rgreenwood]

I have investigated a little further and there is still a problem. The METERS_PER_UNIT seems to be ignored (both the definition that I added for US Survey Feet and the existing definition for the International Foot) The result of a transformation using either "ft" or "us-ft" is returned in meters.
ol.proj.transform([-110.8, 43.5], "EPSG:4326", "EPSG:3739")
[742041.9212159723, 433448.6294142811]
which is incorrect. The correct result in US Survey Feet is:
2434515.870, 1422072.711

[ahocevar]

Careful. This might be a proj4js issue. But I'll take a closer look.

[ahocevar]

Can you share your complete projection definition? Both the proj4js and the ol part.

[rgreenwood]

It SHOULD be a proj4js issue, but I didn't find any unit definitions in the
proj4js-master. The only unit definitions that I could find grep'ing
proj4js and ol3 were in ol3, which does not seem right to me.

Rich

On Wed, Feb 25, 2015 at 5:28 PM, Andreas Hocevar notifications@github.com
wrote:

Careful. This might be a proj4js issue. But I'll take a closer look.

—
Reply to this email directly or view it on GitHub
#3276 (comment).

Richard W. Greenwood, PLS
www.greenwoodmap.com

[rgreenwood]

I started with this:
http://epsg.io/3739.js and ol3.2.1 but no map displayed. After I add:
ol.proj.Units -> USFEET: 'us-ft'
ol.proj.METERS_PER_UNIT[ol.proj.Units.USFEET] = 1200/3937;
my map displayed and I thought that I had the solution.

But regardless of what I do I am getting meters back when I do
ol.proj.transform()
So maybe there are two problems:

1. missing us-ft definition in ol3
2. proj4js not using units

I'm still working on it.

Thanks,
Rich

On Wed, Feb 25, 2015 at 5:31 PM, Andreas Hocevar notifications@github.com
wrote:

Can you share your complete projection definition? Both the proj4js and
the ol part.

—
Reply to this email directly or view it on GitHub
#3276 (comment).

Richard W. Greenwood, PLS
www.greenwoodmap.com

[rgreenwood]

ol3 fails silently (does not request a map) if "projection" does not include a know "units" definition.
epsg.io returns definitions with e.g. "+units=us-ft", however proj4js ver 2.2.1 does not appear to recognize "+units=us-ft" or "+units=ft" and silently defaults to meters.
By adding "+to_meter=0.3048006096012192" to the coord system definition proj4js returns the correct values.

So when using proj4js and epsg.io, any projection that is not in meters transformations will not be correct. This is more of a proj4js issue than an ol3 issue. Adding the us-ft definition that I initially suggested will not solve the problem, but might still be useful in some cases.

[bill-chadwick]

The scale line control needs updating to check for USFEET

[bill-chadwick]

Around line 230