I'm doing some coding in Python with ArcPy with fishnets, and I'm trying to understand more about the tool.
Specifically, the documentation refers to:
The starting pivot point of the fishnet.
The Y-axis coordinate is used to orient the fishnet. The fishnet is rotated by the same angle as defined by the line connecting the origin and the y-axis coordinate.
I'm having trouble understanding, visually, what the origin coordinate is and what the y_axis_coord is. How does this work?
Secondly, I'd like to be able to specify the extent of the fishnet using latitude and longitude, which is an option (I think):
Specify the extent of the fishnet. The extent can be entered by specifying the coordinates or using a template dataset.
How does this option interact with the required parameters of origin_coord and y_axis_coord?
origin_coord is the bottom left corner of your intended output fishnet grid.
y_axis_coord is used to orient the fishnet output. If you want a 'normal' rectangular fishnet you would just take the same x value of the origin_coord and add 1 unit of measure to the y value of the same origin_coord.
you would set a geographic coordinate system output for the fishnet as an environment setting:
env.outputCoordinateSystem = arcpy.SpatialReference([WKID])
and doing the same with the y_axis_coord as per a planimetric CRS you would have the grid formed of lines of lat long, seen as 'rectangular' in the plate carree/equirectangular proj.
Not used it myself but I think the extent would set the maximum bounding extent of the output if the corner_coord is not specified.
"y_axis_coord is used to orient the fishnet output. If you want a 'normal' rectangular fishnet you would just take the same x value of the origin_coord and add 1 unit of measure to the y value of the same origin_coord."
Why does adding one unit of measure make it rectangular?
the orientation of the fishnet is formed from the imaginary straight line drawn between the origin and y axis coord.
In the beautiful picture I've attached, the line is at 0 degrees, meaning no rotation of the fishnet is to be applied.
The second example is a 45 degree angle being formed between the coordinates, and a resultant 45 degree skew being applied.