Georeferenced Control Points/World File

Question

When Georeferencing (DWG CAD data) limited to only 2 Control Points, the alignment is OK, but not great. It automatically produces a World File that I show below.

1. Do the results look odd? They sure don't resemble the ArcGIS Pro Help doc example.

2. And, where values do exist, they do not appear to have anything to do with the Coordinate System ...why?

3. Finally, what do each of these 6 Columns represent? ...The Help doc was confusing to me.

Thanks, CCE

ThomasHoman · Answer

The value represented in the World File only represent the 2 vectors necessary for the linear affine math to do it's job within the currently assigned map projection. This is why the .wld file is only vaild for a single projection - change the projection and .wld breaks.

For your last part to precalulate the .wld file values, I can only say this is way outside my mathematical ability to answer. OSGEO has a discussion of the linear algebra steps that may help your inquiry. https://trac.osgeo.org/postgis/wiki/DevWikiAffineParameters

Craig_Eissler_Iceman · Answer

Thanks, and yes, I understand that concept. With that, I am trying to relate the World File to the Control Points table after Georeferencing the CAD Data in my screenshot. I totally understand the Control Points because these are the geospatial coordinates for the projected coordinate system I'm using. But, I still don't understand what coordinate system the World File values are referencing (especially columns 4 and 5) because I've never seen those values before in GIS. ...If they're just CAD Cartesian coordinates referencing 0,0 somewhere, then I guess I'm wondering what "units" are these in? Another way of asking would be "if I was creating this World File myself (to load into the Georeferencing tool) how would I know what values to use for any of the inputs, including columns 4 and 5?"

ThomasHoman · Answer

Hi Craig,

Sorry for the late response, it took some digging to remember where I had seen the answer. The .wld file is  the information necessary to implement a linear affine process "to move scale and rotate the CAD data from where it was drawn to the proper coordinates..."

https://pro.arcgis.com/en/pro-app/latest/help/data/cad/about-cad-coordinate-systems.htm#ESRI_SECTION1_1A713704A5FA447D839D23E9C9EBC2FB

Hope this helps

Tom