Opinionated Json Converters for ESRI ArcObjects

This project is under development...

A nuget will be available soon.

This library aims to augment interoperability between ESRI ArcObjects and other projects. It provides custom JsonConverters for Newtonsoft.Json to export IGeometry objects to different json formats.

ArcObjects: The start line

ArcObjects are COM components with parameterless constructors, they cannot enforce strict format rules nor object constraints. Therefore, a geometry might be incomplete, incoherent or simply empty depending of where and how it was created. Also, IPolygon or IPolyline (but strangely not IPoint) can always become multi-parts by adding geometries to its collection without altering its geometry type. More over, IMultiPoint can be empty or contain a single point.

The opinions to a finish line

The converters work hard to make the serialization go as smooth and predictable as possible and always assume the worst case scenario: a half baked geometry.

Before serializing a geometry to json, a converter could (depending on GeoJsonSerializerSettings):

• serialize empty geometries as null
• remove paths with less than 2 points
• remove rings with less than 4 points
• change non-simple geometries to simple ones
• auto-correct self-intersections and segment overlaps
• adjust ring orientations: counter clock-wise for exterior rings, clock-wise for holes
• downgrade the geometry type to its "proper" value (see conversion table below)
• generalize paths/rings containing true curves when appropriate

At last, if nothing can be done to serialize the geometry, the converter will complain by throwing an exception.

Conversion Table for ArcObjects Geometries to GeoJson

Definitions

• invalid: denotes a state not appropriate for the type being serialized. For example:

  • a path with a single point
  • a path or ring length smaller than Tolerance
  • a ring with less than 4 coordinates
  • an unclosed ring
  • a polygon without an exterior ring
  • an empty geometry part

Serializer Settings

ForceMulti

Using ForceMulti=false will make the serializer ajust to input geometries. If a Multipoint, Polyline or Polygon contains a single part, the serializer will write a GeoJSON type of Point, LineString or Polygon.

If ForceMulti=true, all ArcObjects types will always be serialized as Multi*, even if they contain a single part, because ArcObjects does not make a distinction between single and multi-parts (excepting Point).

Simplify

Using Simplify=true will use ITopologicalOperator.Simplify() before serializing a geometry. Simplify may remove duplicate geometry parts and may reorient segments in paths and rings. See the official ESRI documentation for this setting.

ArcObjects	GeoJSON	ForceMulti	Simplify	ForceMulti + Simplify
empty or invalid geometry	null	null	null	null
Point	P	P	P	P
Multipoint (single point)	P	MP	P	MP
Multipoint (a point + invalid points*)	P	MP	P	MP
Multipoint (multiple different points)	MP	MP	MP	MP
Multipoint (copies of the same point)	MP	MP	P	MP
Polyline (single path)	L	ML	L	ML
Polyline (duplicated path)	ML	ML	L	ML
Polyline (multi path)	ML	ML	ML	ML
Polyline (single path + invalid paths*)	L	ML	L	ML
Polyline (only invalid paths*)	null	null	null	null
Polygon (single exterior ring)	P	MP	P	MP
Polygon (duplicate exterior ring)	MP	MP	P	MP
Polygon (many exterior ring)	MP	MP	MP	MP
Polygon (exterior ring + invalid exterior ring*)	P	MP	P	MP
Polygon (exterior ring + invalid interior ring**)	P	MP	P	MP
Polygon (only invalid rings)	null	null	null	null
Polygon (only interior rings)	null	null	null	null

Legend
P	Point
MP	MultiPoint
L	LineString
ML	MultiLineString
P	Polygon
MP	MultiPolygon

Notes:

• * Invalid parts are always removed.
• ** Polygon serialized without a hole

Notes

When true curves are present in Polyline and Polygon, the geometry is always generalized, even with Simplify=false. This will eventually be adjusted to only generalize the curved segments.

Licensing

This project is open source under the MIT license.