topic Re: Adding A raster with world file (*.jgw) in ArcGIS Spatial Analyst Questions

Adding A raster with world file (*.jgw)

YairYablovitz — Sun, 10 Apr 2011 08:59:15 GMT

Hi everyone,

I'm trying to add a jpeg file that already has its *jgw world file and suppose to be georeferenced. However, I'm getting a notice that my raster has no spatial reference. Does anyone know how do I add it with the world file?

Your help will be greatly appreciated...

Thanx

Yair

Re: Adding A raster with world file (*.jgw)

EricRice — Mon, 11 Apr 2011 18:52:39 GMT

Hi Yair,

World files do not assign the spatial reference of a raster dataset. The warning is implying that you have not specified the coordinate system for the data. You must define the projection to be the coordinate system that the data was georeferenced to. i.e. Whatever coordinate system was used to create the world file, this is what you need to define the data to be.

These links may be helpful.
Defining or modifying a raster's coordinate system
World files for raster datasets
Fundamentals for georeferencing a raster dataset
Raster coordinate systems

Best Regards,
Eric

Re: Adding A raster with world file (*.jgw)

MikeCasey — Tue, 30 Sep 2014 15:22:06 GMT

Eric,

So you are saying that even though I have a world file, in my case it is a
tif raster and a tfw world file both with the same names (32-91_001.TIF & 32-91_001.TFW)
and I have the Tools\options\raster tab\Use world file to define the
coordinates of the raster checked, that the image/raster will not be referenced
correct in my map?

I have never been able to get a tif file with a world file to reference in a
map. I take that back, I did a while ago but I cannot remember what steps I
took to get it done.

I am currently on ArcMap 9.3.

Re: Adding A raster with world file (*.jgw)

curtvprice — Thu, 02 Oct 2014 03:08:06 GMT

Cosmo, let's break this down a little bit. The "spatial reference" of a geodataset has two parts:

1. Georeferencing

This is the information that maps the internal x,y (row, column in rasters) to real world xy coordinates (decimal degrees, utm meters etc.) This is what lives in your world file, and what inside the geodatabase (unlike a world file, you never see this) to map its internal integer coordinates to x,y values. The georeferencing also (together with the dataset contents) determines the raster or feature class extent, which is hopefully kept in synch with the georeferencing from time to time as the dataset is changed.

2. Coordinate System

This is metadata that tells the software (and you) what the "real-world" xy values mean. For example, are they decimal degrees, and if so which horizontal datum? If they are UTM meters, what zone (and referenced to what geographic datum?)

The CS does not live in your world file, this is created or modified using the Define Projection tool.

IMPORTANT: The Define Projection tool does NOT change the XYs or modify the georeferencing, it just sets up the information (stored in an .aux or .prj file [or in a table row hidden in the gdb]) that tells the software what the XYs mean. If you want to transform data from, say geographic to UTM, you must use the Project or Project Raster tool.

I'm sure if I messed this up Melita Kennedy‌ will set me straight. She's da bomb.

Re: Adding A raster with world file (*.jgw)

LamaZip — Mon, 29 Aug 2016 08:51:26 GMT

Hi Curtis.

If someone wanted to follow the calculation linked here, how would they achieve it?

Re: Adding A raster with world file (*.jgw)

curtvprice — Sat, 17 Sep 2016 21:20:38 GMT

This would entirely specific to the coordinate system of the raster.

If you have a dataset in decimal degrees and you want them as XYs projected (for example, UTM) you'd use the Project tool.

If the file has also been georeferenced with a world file, you'd have to back-calculate using the polynomial specified in the world file. However, I don't have any idea why you would want to do such a thing.