O LLIVIER & C O New Zealand Projections Projections Workshop Basic Projection Steps NZ Transverse Mercator Projections in ArcGIS 8.2 Reprojecting Images Discussion

O LLIVIER & C O New Zealand Projections Moving between Projections Projection: NZMG Units:metres Projection: Geographic Datum: Geodetic 1949 Units: lat/long degrees Projection: NZTM Units:metres Projection: Geographic Datum: NZGD2000 Units: lat/long degrees Datum Transformation 3 or 7 parameter equation or Distortion Grid (NTv2) or None if same datum Unproject Project Unproject Project

O LLIVIER & C O New Zealand Projections Survey Local Circuits They are all Transverse Mercator projections A different series for each datum (1949 and 2000) A different origin for each circuit (28 trig points) A different scale factor for some (Mt Eden and Taieri) Different false origins for each series There is no easy or exact conversion between them NZMG and 1949 circuits are same datum NZTM and 2000 circuits are same datum GPS coordinates are in WGS84 ~ NZGD2000

O LLIVIER & C O New Zealand Projections NZTM - New Sheet Layouts New Zealand Transverse Mercator Metric Topographic Sheets 1: :50,000 series Useful for NZTM Aerial photo tiles

O LLIVIER & C O New Zealand Projections NZTM Sheet Names Similar concept to NZMG Portrait A1 1:50,000 base (prime rectangle) Corrected row x col numbering order 1: :50,000 series height/width ratio 3:2

O LLIVIER & C O New Zealand Projections Using NZ Map Projections or Help! My data doesn’t line up Adapted by permission from an OZRI 2002 presentation by Rose Read, Brisbane ESRI Australia

O LLIVIER & C O New Zealand Projections Why not? Do any layers have unknown coordinate systems? Are layers from different datums? Have you loaded the correct projection files? If two datasets are close ( < 200 metres ) *Usually different geographic coordinate systems (datums). If the datasets differ by thousands or millions of units *Usually the units differ, or *The data is in completely different coordinate systems, or *There are critical bugs in the default NZ projection definitions Load in the patches from or Corax CD *Never use North or South Island Yard Grids

O LLIVIER & C O New Zealand Projections Do any layers have an unknown coordinate system? When zoomed to full extent, a layer does not line up with the other layers Open Data Frame Properties Click Coordinate System tab...

O LLIVIER & C O New Zealand Projections Checking the coordinate systems of the layers Expand Layers. Each layer is listed. Select a layer to see its coordinate system name. Road Centrelines projection is unknown. Data Frame projection defaults to first layer added.

O LLIVIER & C O New Zealand Projections Using ArcMap to identify the unknown coordinate system Set the Data Frame to a new coordinate system and see if the known datasets line up with the unknown dataset If the first one doesn’t work, try some other likely candidates

O LLIVIER & C O New Zealand Projections Does it work? YES Remove the layer from ArcMap Assign the coordinate system of the Data Frame to the layer in ArcCatalog or ArcToolbox Add the layer back into ArcMap

O LLIVIER & C O New Zealand Projections Geodatabase Coordinate Systems Properties Fields tab Click on ‘Shape’ Spatial Reference is listed below

O LLIVIER & C O New Zealand Projections Shapefile Coordinate Systems Properties Fields tab Click on ‘Shape’ Spatial Reference is listed below

O LLIVIER & C O New Zealand Projections CAD Data Coordinate Systems Properties Spatial Reference tab

O LLIVIER & C O New Zealand Projections Raster Coordinate Systems Properties Spatial Reference tab Images will be reprojected on the fly, it may be slower, but it’s a cool feature

O LLIVIER & C O New Zealand Projections Coverage Coordinate Systems Properties Projection tab Can show spatial reference or PRJ file format Update your projection files to include a DATUM

O LLIVIER & C O New Zealand Projections Does it work now? NO Research for more information: Metadata? Data provider or source or age? Similar data types (Map series)? Common coordinate systems used in the area? Check the coordinate extents, each NZ series uses a different range as a hint.

O LLIVIER & C O New Zealand Projections Removing a coordinate system Start ArcCatalog Browse to the dataset and open its Properties Locate the Coordinate System tab Select Clear Click OK

O LLIVIER & C O New Zealand Projections “Missing spatial reference” message When you add data to ArcMap, a warning appears that the data cannot be re-projected. Do not ignore this

O LLIVIER & C O New Zealand Projections What is GCS_Assumed_Geographic_1? Assigned to shapefiles if the coordinate values are between +/-180 for X and +/-90 for Y Allows data to be projected in ArcMap Has no defined transformations

O LLIVIER & C O New Zealand Projections Warning: “geographic coordinate system differs”…

O LLIVIER & C O New Zealand Projections Setting a geographic transformation (to change the Datum) Open Data Frame Properties Select Coordinate System tab Click Transformations

O LLIVIER & C O New Zealand Projections Setting a transformation, continued Convert from: –Lists the geographic coordinate systems of the layers in the data frame Into: –Data Frame’s geographic coordinate system Using: –Predefined transformations

O LLIVIER & C O New Zealand Projections NameLINZ parameters New_Zealand_1949_To_NZGD_2000_1_3PAR New_Zealand_1949_To_NZGD_2000_2_7PAR New_Zealand_1949_To_NZGD_2000_3_NTv220km Distortion Grid TypeAccuracy 3 parameter5 metres 7 parameter4 metres Distortion Grid0.2 metres ArcGIS Datum Transformation Parameter Files

O LLIVIER & C O New Zealand Projections 7 Parameter conversion example /* nzmg_nztm7.prj /* APPROXIMATE NZMG to NZTM (~4 metre error) input projection NEWZEALAND_GRID units meters datum USER_DEFINED parameters output projection TRANSVERSE units meters datum WGS84 SEVEN parameters end ArcInfo Projection Files

O LLIVIER & C O New Zealand Projections Datum Adjustment outside ArcGIS Equivalent NTv2 adjustment can be done using Arc: ADJUST with a cover of links created from the distortion grid. ArcView 3.2 has an extension datum.avx for 3 parameter conversions. Warning: it uses a table of out- of-date 7 parameter figures, but only uses a 3 parameter equation, correct them first. LINZ have a stand-alone nzgd2000.exe to handle single values and bulk text files.

O LLIVIER & C O New Zealand Projections Update your coordinate systems Download the coordinate definition files to overwrite all the NZ files which have the latitude and longitude origins reversed or get from Corax demo CDROM. Delete the North Island and South Island definitions because ArcGIS and ArcInfo projections do not work properly for yards. (Convert them to metres and define some Metric Yard parameter files) Re-arrange the coordinate folders to make them easier to find, move all the others to an Other.

O LLIVIER & C O New Zealand Projections New Sheet Layouts New Zealand Transverse Mercator Metric Topographic Sheets 1: :50,000 series Aerial photographs