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I have a .tif raster file which is based on some projected coordinate system (for example: NAD 1983 State Plane California). I would like to export this raster as a .xyz file, but also reprojecting it to a different projected coordinate system before export (for example to: UTM).

Do I have to reproject the initial .tif raster to WGS84 geographic coordinate system first, then reproject it to desired projected coordinate system (UTM), and then export it to .xyz file?

Or can I directly reproject it from one projected coordinate system to another one (UTM) and export it as .xyz file?

Essentially this is what I am would like to ask:

NAD 1983 State Plane California -> WGS84 -> UTM => export to .xyz

or

NAD 1983 State Plane California -> UTM => export to .xyz

I assume this problem can be applied to a general reprojection from one raster to another (without the need of exporting it to the .xyz file)?

I am using QGIS, but I assume the principle is the same in ArcGIS or other GIS software.

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QGIS and ArcGIS will both convert directly between two projected coordinate systems. Internally, there may be some extra conversions to WGS84 or latitude/longitude on the input or output CRS but you don't need to handle it yourself.

Please note that UTM is part of a projected coordinate system and a UTM zone can be based on many different geographic coordinate reference systems. If the goal is to have NAD 1983 UTM (easting, northing, z) there's no need to pass through WGS84 at all. If the goal is WGS84 UTM (easting, northing, z), then the reprojection might include a geographic/datum transformation as well to convert from NAD83 to WGS84. That will usually occur behind-the-scenes as part of the projCRS-to-projCRS conversion.

  • Thank you for the detailed reply @mkennedy. So the upper quote by GISdirtsniffer: "make sure you deal with the Datum correctly if it is NAD27" is something that will be done automatically behind-the-scenes? – marco Apr 6 '16 at 21:33
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You can go straight from NAD 1983 State Plane California -> UTM => export to .xyz. No need to go to WGS84. When you reproject to UTM, make sure you deal with the Datum correctly if it is NAD27.

  • Thank you @GISdirtsniffer . Forgive me for my ignorance, but what does the 'make sure you deal with the Datum correctly if it is NAD27' mean? That my UTM needs to use NAD27 as the datum? Or something else? – marco Apr 8 '16 at 23:34

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