Projections Workshop Basic Projection Steps NZ Transverse Mercator

Projections Workshop • Basic Projection Steps • NZ Transverse Mercator • Projections in Arc. GIS 8. 2 • Reprojecting Images • Discussion OLLIVIER & CO New Zealand Projections

Moving between Projections Projection: NZMG Units: metres Unproject Projection: Geographic Datum: Geodetic 1949 Units: lat/long degrees Datum Transformation 3 or 7 parameter equation or Distortion Grid (NTv 2) or None if same datum Projection: NZTM Unproject Units: metres Project OLLIVIER & CO New Zealand Projections Projection: Geographic Datum: NZGD 2000 Units: lat/long degrees

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 WGS 84 ~ NZGD 2000 OLLIVIER & CO New Zealand Projections

NZTM - New Sheet Layouts New Zealand Transverse Mercator Metric Topographic Sheets 1: 500 - 1: 50, 000 series Useful for NZTM Aerial photo tiles OLLIVIER & CO New Zealand Projections

NZTM Sheet Names • Similar concept to NZMG • Portrait A 1 1: 50, 000 base (prime rectangle) • Corrected row x col numbering order • 1: 500 - 1: 50, 000 series • height/width ratio 3: 2 OLLIVIER & CO 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 OLLIVIER & CO 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 www. gisuser. co. nz or Corax CD * Never use North or South Island Yard Grids OLLIVIER & CO 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. . . OLLIVIER & CO 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. OLLIVIER & CO New Zealand Projections

Using Arc. Map 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 OLLIVIER & CO New Zealand Projections

Does it work? YES • Remove the layer from Arc. Map • Assign the coordinate system of the Data Frame to the layer in Arc. Catalog or Arc. Toolbox • Add the layer back into Arc. Map OLLIVIER & CO New Zealand Projections

Geodatabase Coordinate Systems • • Properties Fields tab Click on ‘Shape’ Spatial Reference is listed below OLLIVIER & CO New Zealand Projections

Shapefile Coordinate Systems • • Properties Fields tab Click on ‘Shape’ Spatial Reference is listed below OLLIVIER & CO New Zealand Projections

CAD Data Coordinate Systems • Properties • Spatial Reference tab OLLIVIER & CO 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 OLLIVIER & CO 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 OLLIVIER & CO 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. OLLIVIER & CO New Zealand Projections

Removing a coordinate system • Start Arc. Catalog • Browse to the dataset and open its Properties • Locate the Coordinate System tab • Select Clear • Click OK OLLIVIER & CO New Zealand Projections

“Missing spatial reference” message • When you add data to Arc. Map, a warning appears that the data cannot be re-projected. • Do not ignore this OLLIVIER & CO 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 Arc. Map • Has no defined transformations OLLIVIER & CO New Zealand Projections

Warning: “geographic coordinate system differs”… OLLIVIER & CO New Zealand Projections

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

Arc. GIS Datum Transformation Parameter Files Name LINZ parameters New_Zealand_1949_To_NZGD_2000_1_3 PAR 54. 4 New_Zealand_1949_To_NZGD_2000_2_7 PAR -59. 47 -5. 04 187. 44 -0. 47 0. 10 -1. 024 -4. 5993 New_Zealand_1949_To_NZGD_2000_3_NTv 2 20 km Distortion Grid Type Accuracy 3 parameter 5 metres 7 parameter 4 metres Distortion Grid 0. 2 metres OLLIVIER & CO -20. 1 183. 1 New Zealand Projections

Arc. Info Projection Files 7 Parameter conversion example /* nzmg_nztm 7. prj /* APPROXIMATE NZMG to NZTM (~4 metre error) input projection NEWZEALAND_GRID units meters datum USER_DEFINED 59. 47 -5. 04 187. 44 -0. 47 0. 10 -1. 024 -4. 5993 parameters output projection TRANSVERSE units meters datum WGS 84 SEVEN parameters 0. 9996 173 00 00 00 1600000 10000000 end OLLIVIER & CO New Zealand Projections

Datum Adjustment outside Arc. GIS • Equivalent NTv 2 adjustment can be done using Arc: ADJUST with a cover of links created from the distortion grid. • Arc. View 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 nzgd 2000. exe to handle single values and bulk text files. OLLIVIER & CO 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 South Island definitions because Arc. GIS and Arc. Info 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. OLLIVIER & CO New Zealand Projections

New Sheet Layouts New Zealand Transverse Mercator Metric Topographic Sheets 1: 500 - 1: 50, 000 series Aerial photographs OLLIVIER & CO New Zealand Projections