0

I typically don't use ArcMap (and so my skill level in using it is low) but use R instead, but for a validation process I need to compare outputs between ArcMap and R. As part of a small step in this process, I created an animal's utilization distribution raster in RStudio and saved it with the following CRS:

"+proj=aeqd +lat_25.6871 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs"

I then imported this raster into ArcMap. When I navigate to the "Source" tab of the "Layer Properties" panel (right click raster layer in "Table Of Contents"), I find that its "Spatial Reference" is undefined and "XY Coordinate System" is unknown. It's extent is roughly -17k to +17k for x coordinate and -12.5k to +12.5k for y coordinate (raster's center/origin is 0, 0).

I need its projected coordinate system to be that of "WGS_1984_UTM_Zone_17N", as this is the CRS of my study site shapefile (which also has the following projection: "Transverse_Mercator" and following extent: top: ~2.852k, right: ~677k, bottom: ~2.838k, left: ~669k), so that I can plot the data onto the study site.

Because after I import the raster into ArcMap for the first time I get the "Unknown Spatial Reference" warning, I use ArcMap's built-in tool "Define Projection", select my raster as input dataset, and select the projected coordinate system "Azimuthal Equidistant (world)" as the coordinate system to be applied to the input. (The second step would be to use the "Project Raster" tool to reproject aeqd to UTM Zone 17, but this step doesn't/couldn't work if the first step returns an empty geometry.)

While the "Define Projection" tool does not return an error, the result seems to be an empty raster i.e. when I right-click on the newly created raster and select "Zoom To Layer", nothing is shown even though the check box is ticked.

Any idea what's going on?

enter image description here

I can import the raster and define projection with epsg 32617, which is WGS84 UTM17N, and you can see that the raster is centered over 0,0 of UTM17N. The proj.4 string is

"+proj=aeqd +lat_0=44.99489997 +lon_0=-17.48575004 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs"

but there doesn't seem to be any way to define projection with a proj4 string. When I attempt to do this, I get the ArcMap define projection proj.4 error

000735 coordinate system value is required

ArcMap help says "all required parameters must have a value provided. For help in determining whether a parameter is required or optional, look under the syntax sections of the tool's help page".

But the syntax section in the Define Projection help url doesn't say which proj4 elements are required.

Can Define Projection accept proj.4 strings?

Is my proj.4 string missing something?

Am I going about this the wrong way?

12
  • 3
    Wait, why, if you need WGS_1984_UTM_Zone_17N do you choose "Azimuthal Equidistant (world)" and not WGS_1984_UTM_Zone_17N? These are very different projections. It's rare that Define Projection is appropriate, but you are correct in tool choice; you just need to select the correct projection.
    – Vince
    Commented Sep 8, 2022 at 13:05
  • 1
    Okay, please Edit the Question to focus on the steps you have performed (Define as actual CRS and Project Raster to reproject) and the error that resulted.
    – Vince
    Commented Sep 8, 2022 at 17:01
  • 1
    No, the second attempt can't work, so that shouldn't be documented. The first attempt is the correct path and the error received is the problem. That error should be documented in the Question (exact text), along with the "Copy as Python snippet" of the actual command from the Geoprocessing log (with privacy redactions as necessary).
    – Vince
    Commented Sep 9, 2022 at 11:07
  • 1
    "Newly created raster" doesn't make sense (defining the projection only adds a .prj/.xml to an existing raster), nor does "empty geometry" -- rasters don't have a geometry. Even if the raster is all nodata, it still should have an extent. Pull up the raster in the Catalog window and right-click on Properties... What does it show for extent?
    – Vince
    Commented Sep 13, 2022 at 11:29
  • 1
    Unless you're always mapping Null Island, centered on {0,0} for a global projection doesn't seem right.
    – Vince
    Commented Sep 14, 2022 at 14:37

1 Answer 1

0

From what you describe, your raster is not in any standard coordinate system yet. It has no projection. The tools for defining a projection really only assign the projection metadata to describe what is already true about the coordinates of the raster. In other words, if you had a raster that was in UTM 17N, the "define projection" tool simply tells ArcGIS that it is in 17N. It changes nothing about the coordinates themselves.

What you want to do is georeference your raster. To do that, you will need to know the projected coordinates for a number of control points. (The extent corners will work.) For reference, see https://desktop.arcgis.com/en/arcmap/latest/manage-data/raster-and-images/fundamentals-for-georeferencing-a-raster-dataset.htm

1
  • Thanks! I'm going to look into it, your explanation makes sense. I saw this link before, but didn't realise it could be the solution to my issue. I'll get back to you. Commented Sep 22, 2022 at 15:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.