Most geospatial data types support points, lines and polygons only. When Bentley Map exports or post features it converts the various MicroStation geometries into one of those types. When there are curves or arcs in the linear or polygon element or when circles or ellipses are transferred these are stroked into line strings using a defined tolerance.
What can occur is that the tolerance (distance between the original arc and stroked line string) may appear to vary or simpler stated, the transferred element looks very different from the original one. The problem is illustrated in the figure below where the element in blue is stroked with very few line segments (edges) and it doesn’t look any close to the original element in red. For example measurements of the area can be altered in case of polygons if this occurs.
Bentley Map uses a variable to define the stroke tolerance. This tolerance can be adjusted with ECSDK_GEOMETRY_STROKING_TOLERANCE. It represents the maximum distance between the actual element and the approximating line in master units. This configuration variable can be set at environment or workspace level and is used to change the stroking tolerance.
The problem described above can occur for example when exporting to a TAB file or when the data is stored in an Oracle spatial database, if a non-supported non-linear geometry is encountered while posting to the spatial database (in this example a 3D Arc), the geometry is stroked before being inserted in the database.
The stroking tolerance is computed based upon the layer tolerance so the variable ECSDK_GEOMETRY_STROKING_TOLERANCE should be set as an optional override to the default stroking tolerance in the Interoperability application.
In an Oracle spatial project we can set this variable at the workspace level in the Bentley Map Geospatial Administrator under Workspace > Macro.
The figure below represents as in the first figure the original element in red and the data that was posted and later is queried in blue. This turn when using the stroking tolerance of 0.01 where the original is the red arc and the approximating line is blue the result is considerable improved. In practice, a much smaller stroking tolerance will yield better results.
More information about the exporting features can be found in the Bentley Map Help documentation