arcgis-10.4arcgis-desktopbufferellipsepolygon
I'm using ArcMap to draw polygons around some geologic features. I want to know the length of the semi major and semi minor axes of the smallest ellipse that would fit around the polygons.
I'm a new Arc user, so it's possible that there's a simple way to do this, but not that I've yet found. Maybe the buffer tool could do the trick, but I'm not sure how.
I've done similar work before, for rotation, there is rotate function for polygons. In your case, add following line before adding feature to the layer:
var originPoint = new OpenLayers.Geometry.Point(xCent, yCent).transform(map.displayProjection, map.projection); //center point for rotation
polygonFeature.geometry.rotate(rot, originPoint);
You can find full documentation about rotate function here
I'm not sure about your calculation for the ellipses(you might have used some mathematical transformations), but I would suggest to use the polar system to get those points coordinates.
Get the distance from the point on ellipse at direction θ to the origin using following formula:
The coordinates of the point are:
x = r(θ) * cos(θ)
y = r(θ) * sin(θ)
While arcpy Geometry objects do not support true curves, at 10.3, Esri implemented True Curves in the REST API, and therefore had to implement JSON support for them in FeatureSets. So you can "trick" arcpy into doing this for you if you create a curve in a JSON structure.
Here's an example: create a JSON file with true curves (this uses a circular arc and a Bezier curve), something like this:
{ 'fieldAliases': {
'Id': 'Id',
'FID': 'FID'
},
'fields': [{
'alias': 'FID',
'type': 'esriFieldTypeOID',
'name': 'FID'
}, {
'alias': 'Id',
'type': 'esriFieldTypeInteger',
'name': 'Id'
}],
'displayFieldName': '',
'spatialReference': {
'wkid': 103734,
'latestWkid': 103734
},
'geometryType': 'esriGeometryPolyline'
'features': [{
'geometry': {
"curvePaths":[[
[6,3],[5,3],
{"b":[[3,2],[6,1],[2,4]]},
[1,2],
{"a":[[0,2],[0,3],0,0,2.094395102393195,1.83,0.33333333]}
]]
},
'attributes': {
'Id': 0,
'FID': 0
}
}],
}
Then, load that into a feature set and save it out to a Feature class.
fs = arcpy.FeatureSet()
fs.load(r'C:\path_to_your_json_file.json')
arcpy.management.CopyFeatures(fs, r'in_memory\test_curve')
And boom, you have true curves! This is what it created in ArcMap:
So in your case, maybe you can build a json structure by either casting the original features to a feature set and playing with the JSON, or as you iterate through rows in a search cursor. The math may be a little tricky to get what you want, but definitely is doable.
I should also mention that you don't have to form a full feature set, you can just pass the JSON geometry directly into the arcpy.AsShape(geojson, True) as well to get a geometry object back.
Best Answer
You could refer to Esri's documentation Creating an ellipse feature
Alternatively, you may try as this user Make a minimum bound ellipse? suggests, you would need an extension via ArcMap
To add from my comments:
Here is an Esri idea page [Minimum bound ellipse](https://community.esri.com/ideas/6118