Go to ET GeoWizards 12.x User Guide
ET GeoWizards and
Projections
Some short definitions(compiled from ArcGIS desktop help)
- Projection - The
two-dimensional representation of the three-dimensional space.
- Coordinate System - a reference
system for measurements defined by the projection
- Geographic Coordinate System
- measures locations in degrees - latitude and longitude. Since latitude and
longitude are angular measurements they are not suitable for measuring distances. The
major parameter of a Geographic Coordinate System is its datum
- Projected Coordinate System - uses a projection to transform the latitude and longitude
to X and Y coordinates and makes the linear measurements more accurate. Each projected
coordinate system is based on a Geographic Coordinate System
- Spatial Domain - the range and precision of coordinates that can be stored in a
feature dataset
- Spatial Reference - contains information for the coordinate system and spatial domain
extent for a feature dataset
Projections of the data ( for feature classes the projection information is
stored in the feature classname.prj file)
- Projected data - the data is explicitly projected in a Projected Coordinate System
- Unprojected data - the data is in a Geographic Coordinate System
- Data with unknown projection - the
projection information ( in the case of feature classes - "feature classname.prj")
is missing
Projections of the dataframe (View)
- No projection - the data is displayed as is
- Assigned projection - the data is reprojected on the fly and displayed in the data
frame's projection.
ET GeoWizards works with data in any projection and view frame in any
projection
Notes:
- All the wizards preserve the Spatial Reference of the input data source. The assumption
is that if the user keeps a dataset in certain projection he has reasons for that,
and all the products of this data set must be in the same projection.
- When a distance input is required ( Fuzzy tolerance, Dangling tolerance etc. )
best results will be achieved if the data is projected in a specific projection and the
data frame does not have projection (or has the same projection as the data), because the
tolerance is compared directly with the data.
- The Wizards will not work if the data frame contains one or more layers that have
projection with Geographic Coordinate System different from the Geographic Coordinate
System of the data frame's projection. ArcMap gives a warning in such a case, but allows
it.
- Although possible, it is not recommended to manipulate Unprojected data (data in a Geographic Coordinate System) for reasons
mentioned above
- If the projection information is
missing, the data can be manipulated only in a data frame with no projection assigned.
Copyright © Ianko Tchoukanski |