If the specified source coordinate system is “Read from feature” or blank, the input feature’s coordinate system is used as the source. In this case, if the input feature doesn’t have a coordinate system, this transformer only sets the coordinate system of the feature to the destination coordinate system, and the coordinates of the feature remain unchanged.
This parameter specifies what geographic transformation will be used to convert points from the source datum to the destination. If set to <Auto>or left blank, FME will attempt to choose an appropriate transformation. If set to <None>, the NULL_FME transformation will be used which does not alter the value of any coordinates.
Note: <Auto> and <None> are GUI only values. Use the alternative blank string and NULL_FME respectively when passing in as an attribute.
This parameter determines how Z values will be handled:
- Ignore heights and leave them unchanged: Z values will not affect the reprojection and will not be changed. This is the traditional behavior of the Reprojector transformer when the selected reprojection engine is “FME”.
- Heights are relative to the ellipsoid(s) or geocentric: Z values will be treated as ellipsoid heights with the same units as the horizontal units (or meters, for geographic coordinate systems). If the source coordinate system is geocentric, coordinates will be converted to geographic+ellipsoid height before being processed. If the destination coordinate system is geocentric, coordinates will be converted to geocentric after being processed.
Geocentric or ellipsoid height -> Orthometric height: Z values will be converted from ellipsoid height to orthometric (sea level) height given the specified geoid height grid. Z units will be the same as the horizontal units (or meters, for geographic coordinate systems). If the source coordinate system is geocentric, coordinates will be converted to geographic+ellipsoid height before being processed.
Example: [Geocentric (datum A) ->] LL + ellipsoid height (datum A) -> LL + ellipsoid height (datum B) -> LL + orthometric height (datum B)
Orthometric height -> Geocentric or ellipsoid height: Z values will be converted from orthometric (sea level) height to ellipsoid height given the specified geoid height grid. Z units will be the same as the horizontal units (or meters, for geographic coordinate systems). If the destination coordinate system is geocentric, coordinates will be converted to geocentric after being processed.
Example: LL + orthometric height (datum A) -> LL + ellipsoid height (datum A) -> LL + ellipsoid height (datum B) [-> Geocentric (datum B)]
- NAD27 heights in NGVD29; NAD83 heights in NAVD88: VERTCON will be used to convert between NAD27 (NGVD29) and NAD83 (NAVD88). Z values have the same units as the horizontal units (or meters, for geographic coordinate systems).
Note: Note that rasters can only be reprojected in 2D (that is, with Ignore heights and leave them unchanged).
This parameter determines which geoid height grid will be applied to the Z values of coordinates.
FME supports the following vertical grid formats:
- Geoid96 (GEO)
- Geoid99 (bin)
- OSGM91 (txt)
- Byn (byn)
- Egm96 (grd)
The CsmapReprojector can apply grids in any of these formats via a .gdc file, which is a text file that list one or more grid files in the formats listed above. Grids will be tried in order until one is found that provides coverage for the point being transformed. Grid files may be listed with absolute paths, or by paths relative to the .gdc file.
Example .gdc file contents for a grid file in the same folder as the .gdc:
# comments start with '#' ./CGG2000.byn
Some of the .gdc files shipped with FME reference grid files that are not included in the Desktop installer. You can download those grid files from at http://www.safe.com/support/support-resources/fme-downloads/beta/.
See Vertical Grids for more information.
The Interpolation Type affects only raster data. Cell values are interpolated in order to change the raster to the specified size.
- Nearest Neighbor is the fastest but produces the poorest image quality.
- Bilinear provides a reasonable balance of speed and quality.
- Bicubic is the slowest but produces the best image quality.
- Average 4 and Average 16 have a performance similar to Bilinear and are useful for numeric rasters such as DEMs.
The Cell Size applies only to raster features.
- Stretch Cells: The cell size of the raster will be adjusted to maintain the same number of rows and columns in the reprojected raster as there were in the input raster.
- Square Cells: The number of rows and columns as well as the spacing will be changed to maintain approximately the same cell ground area and form square cells where the horizontal and vertical cell sizes are equal.
- Preserve Cells: Like the Square Cells option, this option will change both the number of rows and columns and the spacing to maintain cell ground area, but will also try to preserve the original cell aspect ratio, taking into account any warping caused by the reprojection.
Sets the tolerance, in cells, for approximating cell locations for raster reprojection.
If a value of 0.0 is specified, every cell location in the raster will be reprojected. This is the default.
If a value > 0.0 is specified, rather than reprojecting every single cell location in the raster, some cell locations will be approximated. The difference between an approximated cell location and the true cell location should be at most the tolerance value. For example, if a value of 0.5 is specified, each approximated cell location should be at most half a pixel away from its true location. Specifying a value > 0.0 may improve performance.
Dynamic Coordinate Systems
If the destination coordinate system is specified as "_AZMEA_" or "_AZMED_", each input feature is reprojected to either an equal area or equal distance projection appropriate for that feature, respectively. In general, this causes a new coordinate system to be defined for each input feature.
Each feature remembers which specific equal distance or equal area coordinate system it has, and can be safely reprojected back to a normal (non-dynamic) coordinate system.
There is an input feature representing a point on the earth in LL-WGS84 (normal lat/long).
- The point is reprojected to _AZMED_ via a CsmapReprojector transformer. The Source Coordinate System parameter is set to LL-WGS84 and the Destination Coordinate System parameter is set to _AZMED_.
- The x and y coordinates of the point are extracted into x1, y1.
- Set x2 = x1 + 1000, and y2 = y1.
- Add a vertex to the point to make the line (x1,y1) -> (x2,y2).
- Reproject back to LL-WGS84 via a CsmapReprojector with the Source Coordinate System parameter set to ”Read from feature” and the Destination Coordinate System parameter set to LL-WGS84.
You have now changed the point into a line extending 1km east of the original point, in lat/long.
Dynamic coordinate systems have the following limitation:
- Z is not considered, so areas or distances are best preserved for geometry at an ellipsoid height of 0 meters.
- This transformer works with raster, vector, and point cloud data.
- This transformer is unaffected by raster band and palette selection.
Editing Transformer Parameters
Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click beside the applicable parameter. For more information, see Transformer Parameter Menu Options.
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