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Tuesday, 9 June 2015

Map Projection Headache

Recently, I was thrown into map projection issue and this pushed me to my technical limit. For this article, I will not reveal the full context of the area it happened due to privacy reasons. I was tasked to identify the locations of new road intersections, geometries and other road aspects for new housing subdivision. This task is important as the organization needs to submit these new roads information to state government in a particular format (not in GIS format).

The reason this task became a map projection issue is because the drawing file that was supplied to me had a projection that was unknown to me. The organization contracted an external party who surveyed the locations of the new roads. The projection they used was customized UTM for the subdivision area. Originally, when the drawing file was supplied, the projection parameter was not visible in QGIS. For this work, I had ArcGIS and QGIS only and no FME or any other projection converter to help.

I approached the organization to supply the coordinate system that is attached to the drawing file. I stumbled upon a projection (let’s call it Projection A) that I have not encountered before. Fortunately, the organization supplied the parameters that is needed for ArcGIS/QGIS to visualize the line works.

Having said, I need to match the location of these new roads with the organization’s existing road network. Having no experience about Projection A, I made an attempt to do direct projection conversion from Projection A to one of the MGA zones (where the subdivision is located). The outcome was not desirable as the subdivision was positioned in the sea! After making some futile attempts to convert, I gave up on my own approach.

The following day, I contacted the state roads department on the projection A parameters and conversion process. The person who manages the section was kind enough to spend her time to walking the process. I had to de-project Projection A to GDA and reproject it back to MGA projection. Since I was use ArcGIS for this process, I contacted one of my ESRI contacts on how to implement this process in ArcMap. He worked out the implementation process (he was kind of puzzled by the name of the projection A).

I had a serious relook into projection parameters I initially set in Projection A and corrected any inaccuracies. Following the procedures outlined by state roads department and ESRI, I successfully brought the new roads into alignment with existing road network. It was Momentous occasion as it solved my riddle for past two days.

Below here is attached image of the new roads that pushed my mental skills.
New roads of a new subdivision which aligned well with existing road network
Due to privacy reasons, the location of the roads, the name of the projection, organization and state road department are kept hidden.