Configuring Projections

5.6.2+

You may select a Projection for your Map Source by picking an entry from the list. There is a default Projection that is configured via the iShare Settings on the General tab under the Web heading.

In previous versions of iShare the .map file points to the Projections supplied by MapServer which contains a long list of SRID without any descriptions. Astun now supply a cut down Projection file in a projections folder that will not be overwritten if MapServer is upgraded e.g. D:\iShareData\Astun\_MapServerConfig\projections\epsg

The order in which you specify the entries in this file will be the order that they are displayed in Studio i.e. put the most used projections at the top of the list.

Configure your .MAP file to use the new Projections file

If you wish to use this file instead of the default MapServer projection file you will need to edit your .map file to point to the new projections file by changing the CONFIG "PROJ_LIB" entry e.g.

CONFIG "PROJ_LIB" "projections"

Adding your own Projections

You may add your own Projections by opening the file in a Text Editor such as Notepad++. The entries must be formatted correctly to display in the list correctly e.g. for BNG

# OSGB 1936 / British National Grid
<27700> +title=British National Grid +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +units=m +no_defs <>

The first line is just a comment the next has the following formatting requirement:

Code	Descrption
<27700>	The SRID for the projection
+title=British National Grid	The Title to display
`+proj=tmerc` `+lat_0=49` `+lon_0=-2` `+k=0.9996012717` `+x_0=400000` `+y_0=-100000` `+ellps=airy` `+datum=OSGB36` `+units=m` `+no_defs`	The Projection definition. In order to find the correct definition for your required projection please see http://spatialreference.org/ref/ select the relevant entry and then click on the Proj4 link which will give you what you require.
<>	The end of line

Remember that your Map Sources may be set up for WMS & WFS access. If your Map Sources' associated .map files are set up to support multiple projections then make sure the epsg file referenced contains all the necessary projection definitions. Below is a typical epsg file shortened to only include projections typically used with British data.

# WGS 84
<4326> +title=long/lat:WGS84 +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs  no_defs <>
 
# ETRS89
<4258> +title=long/lat:ETRS89 +proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs  no_defs <>
 
# OSGB 1936 / British National Grid
<27700> +title=British National Grid +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs  <>
 
# TM75 / Irish Grid
<29903> +proj=tmerc +lat_0=53.5 +lon_0=-8 +k=1.000035 +x_0=200000 +y_0=250000 +a=6377340.189 +b=6356034.447938534 +units=m +no_defs  no_defs <>
 
# OSNI 1952 / Irish National Grid
<29901> +proj=tmerc +lat_0=53.5 +lon_0=-8 +k=1.000000 +x_0=200000 +y_0=250000 +ellps=airy +units=m +no_defs  no_defs <>
 
# IRENET95 / Irish Transverse Mercator
<2157> +proj=tmerc +lat_0=53.5 +lon_0=-8 +k=0.999820 +x_0=600000 +y_0=750000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs  no_defs <>
 
# SR-ORG:6864
<3857> +proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378137 +b=6378137 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>
 
# EPSG:3035
<3035> +proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs <>