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Reprojecting raster land cover data

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09-07-2023 03:16 AM
ErikaMae
New Contributor

Hi all, 

My ultimate goal is to conduct change detection analysis on mangrove and non-mangrove extents for my study area over the years 2012, 2017, and 2021. I acquired my data through supervised classification on Google Earth Engine and exported my mangrove extents as GeoTiffs. It was exported at a scale of 30m (as I used Landsat) and the default coordinate reference system EPSG:3857. The image below is a screenshot of one of the exported tiffs properties. 

ErikaMae_0-1694080356254.png

ErikaMae_1-1694081687974.png

 

My study area of Moreton Bay, Queensland is set to the coordinate system Geocentric Datum of Australia 1994. I will go on to use the Change Detection Wizard tool to map the changes between study years. 

For what I am setting out to do, do I need to reproject to the Australian geographic coordinate system? Also, if I have exported the GeoTiff at a scale of 30m, why in the ArcGIS Pro layer properties is the cell size 0.000269?

 

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2 Replies
DuncanHornby
MVP Notable Contributor

Unless the change detection wizard requires your data to be projected you can probably leave your data in a WGS84 coordinated system and use it without projecting.

30m at the equator is 0.000269 in decimal degrees, you can have a play using this web page.

If you are attempting to report change in m2 then you are best projecting your raster into a coordinate system where the units are in metres and not decimal degrees. Summary lengths /area will make more sense.

You'll need to do a little research for what's best for mapping area in the region of Moreton Bay, Queensland. 

ErikaMae
New Contributor

Thank you for your response Duncan!

As far as I'm aware the change detection wizard doesn't require reprojection, but I wonder if calculating the area for the catchments later would be impacted by not reprojecting?

I've seen mangrove extents measured in hectares which I was planning on using too, however, the extents are quite small so I think a smaller unit like m2 might be more fitting. 

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