* add support for Projection Gauss_Kruger

[quyihang]

Gauss_Kruger uses the same method like Transverse_Mercator. Add Gauss_Kruger projection alias name to lib/projections/tmerc.js so wkt like this can be support:

PROJCS["CGCS2000_3_Degree_GK_CM_111E",GEOGCS["GCS_China_Geodetic_Coordinate_System_2000",DATUM["D_China_2000",SPHEROID["CGCS2000",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Gauss_Kruger"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",111.0],PARAMETER["Scale_Factor",1.0],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]

[rockdai]

Hi, @ahocevar Would you please take a look at this PR, I do need this feature too, whether it can be accepted?

[rockdai]

/cc @calvinmetcalf

[ahocevar]

@rockdai Where did you find a WKT string with Gauss_Kruger as projection? epsg.org lists this as official WKT v1 string for EPSG:4546:

PROJCS["CGCS2000 / 3-degree Gauss-Kruger CM 111E",GEOGCS["China Geodetic Coordinate System 2000",DATUM["China 2000",SPHEROID["CGCS2000",6378137,298.2572221,AUTHORITY["EPSG","1024"]],AUTHORITY["EPSG","1043"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9102"]],AXIS["Lat",north],AXIS["Lon",east],AUTHORITY["EPSG","4490"]],PROJECTION["Transverse Mercator",AUTHORITY["EPSG","16319"]],PARAMETER["Latitude of natural origin",0],PARAMETER["Longitude of natural origin",111],PARAMETER["Scale factor at natural origin",1],PARAMETER["False easting",500000],PARAMETER["False northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["X",north],AXIS["Y",east],AUTHORITY["EPSG","4546"]]

Note: projection is Transverse Mercator. I did not find any other occurrence of a WKT string with Gauss_Kruger as projection.

[rockdai]

@ahocevar From what I can see, Gauss-Kruger is just another name for transverse mercator.
Here is an example, please search "4528" on this page: https://developers.arcgis.com/javascript/3/jshelp/pcs.html

[rockdai]

ping @ahocevar

[ahocevar]

Sorry for leaving this unreviewed for way too long. You are right, @rockdai. Any chance you could update your pull request? The change would now have to be made in etmerc.js instead of tmerc.js, and it would be good if you could add a test.

[quyihang]

Sorry I did not read this repo for a long time. In order not to ruin other codes, could you update it and close this PR if you think it’s necessary? Many thanks.