Projections

ConfirmConnect®, ConfirmWorkzone®, and Confirm web are capable to transform all data coming from Confirm into your specified coordinate system, so that it can be displayed properly on the map. The popular visualisation system (EPSG:3785) used by Google and Bing is included as a standard. But for other coordinate systems, the definition needs to be provided, which is required for all map service types.

The definition for a coordinate system should be provided on Web Map Settings as follows:

"projection":

This is the EPSG code of the coordinate system that you want to use. E.g. "EPSG:27700" is the EPSG code for British National Grid.

"projectionDef":

ConfirmConnect® uses the Proj4 format for coordinate system definitions.

You can find the Proj4 definition for your coordinate system here: http://spatialreference.org/.

For example, http://spatialreference.org/ref/epsg/27700/proj4/ gives:

+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

Note: Enter this on a single line in the projectionDef parameter.

Grid Shift

Some countries apply a grid shift in order to provide high accuracy coordinate conversions from default GPS coordinate systems into their own native coordinate systems. For example, in the UK the Ordnance Survey base maps use the OSTN02 grid. See the section entitled The National Grid transformation OSTN02 on the Ordnance Survey website for details.

In order for ConfirmConnect®, ConfirmWorkzone®, and Confirm web to accurately plot entities on map where this type of conversion is required, Confirm needs to be notified of the grid used so the grid shift file can be included. These files have not all been included by default due to their initial size and potential performance implications.

The OSTN02 grid shift file has been included with ConfirmConnect®, ConfirmWorkzone®, and Confirm web, if you use OS background maps, you will need to include an additional projectionDef value. Append '+nadgrids=ostn02' onto the end of the current line. For example:

+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 +nadgrids=ostn02

GDA2020

Confirm supports the new GDA2020 coordinate reference system.

A GDA94 projection can be converted to a GDA2020 projection by adding another projectionDef value which is “+towgs84=-0.06155,0.01087,0.04019,-0.0394924,-0.0327221,-0.03289790,0.009994”.

For example:

The projection definition for MGA zone 55 from spatialreference.org is:

"+proj=utm +zone=55 +south +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs"

Which can be converted to GDA2020 as follows:

"+proj=utm +zone=55 +south +ellps=GRS80 +towgs84=-0.06155,0.01087,0.04019,-0.0394924,-0.0327221,-0.03289790,0.009994 +units=m +no_defs"

Note: Note: Enter this in a single line in the projectionDef parameter.