I'm working with this downloadable shapefile that has X Y coordinates. They are akin to '3672187.92698000, 534175.72095400'.
I would like to convert them to longitude latitude so they are more like '-90.097017, 29.963176'.
I've seen this question tackled using ArcMap however I don't have that software. I was able to download and install QGIS but I am unfortunately perplexed by its complicated interface. Would like to do the conversion with it, if possible.
The dataset you mention is a shapefile, a format invented by ESRI, but understood by most GIS software, including QGIS.
After extracting the zip, you can add it with Add vector layer and point to the .shp file. The CRS information is stored in the .prj file, and the layer CRS will automatically set right by QGIS. In your case, NAD_1983_StatePlane_Louisiana_South_FIPS_1702_Feet with US feet as units.
With the openlayers plugin, you can add a Openstreetmap or Google background layer. For doing that, you have to set the project CRS to EPSG:3857.
If you want coordinates in lat/lon degrees, just rightclick on the shapefile layer, and Save as ... to a new file under a different name, selecting EPSG:4326 as CRS for that, and check to add that layer to the canvas. Saving may take some time.
For the next step, you better zoom in to see just a couple of points.
Open the attribute table, and click on the pencil symbol at the bottom to enter the edit mode, and then the field calculator icon bottom right. Create a new field named degx, type real, precision 6, and select $x from geometry. After saving (which takes some time), do the same for degy and $y. Leave edit mode, then the attribute table.
The new columns in the attribute table give you lat and lon in degrees.
You can import the coordinates as a csv, e.g. in a file called coords.csv you would have:
x, y
672187.92698, 534175.72095
1) Import it by Layer -> Add delimited text layer.
The next dialogue should be fairly self explanatory. After clicking OK from this dialogue you will be asked for the coordinate system of your input coordinates. You can work through the list or use the Filter box to help find the right projection.
2) Once it's imported right click on the layer in the Layers panel, and choose "Save as".
3) Save it as a shapefile, and change "Layer CRS" to "Selected CRS", then browse the projections to find WGS84 EPSG:4326. Select to add it to the map and click ok.
4) Once your new shapefile is created, right click on it the layer's dialogue and "Open Attribute Table". Toggle editing (ctrl-E) and open the calculator (ctrl-I). Select "create a new field", call it "Longitude", and make the expression $x. Do the same for a second new attribute called "Latitude" and make the expression $y. You should now have latitude and longitude in your attribute table.
5) If you want it in a spreadsheet a quick solution is to click on the invert selection icon (Ctrl-R) and then copy to clipboard (Ctrl-C). You can then paste it directly into a spreadsheet.
Your question is not ArcGIS/QGIS specific. It has to do with coordinate systems. I interpret your questions as "How do I import X/Y csv data in one spatial coordinate system and export to another coordinate system using QGIS?".
If you do not have your data displaying correctly in QGIS (assuming v1.8), you will need to enable the "Add Delimited Text Layer" plugin using the Plugin Manager, then import the data using Layer -> Add Delimited Layer, then proceed through the wizard selecting the appropriate source, x/y columns, and then the correct coordinate system.
They layer should now be correctly displaying in QGIS in it's native coordinate system. If you want to reproject it on the fly, you will need to go to Settings -> Project Properties -> Select "on the fly reprojection" and the desired display coordinate system.
Now that you have the data properly imported, all you have to do is right click your layer and select "Save As". In this dialog, change to the format you would like (shape, csv, etc), set a save location, and in the CRS section select "Selected CRS", then click Browse and select "WGS 84" or any other desired coordinate system.
You can reproject geometry with a QGIS expression. Here’s an example of how you can convert from one EPSG to another using QGIS expression1:
format_number(x(transform($geometry, layer_property(@layer,'crs'), 'EPSG:4326')),6)
format_number(y(transform($geometry, layer_property(@layer,'crs'), 'EPSG:4326')),6)
In this example, the geometry is being transformed from the layer’s CRS to EPSG:4326. You can change the value of the target EPSG to the one you want to convert to.
