O LLIVIER & C O New Zealand Projections Projections Workshop 2004 Basic Projection Steps NZ Transverse Mercator Projections in ArcGIS 9.0 Reprojecting.

Presentation on theme: "O LLIVIER & C O New Zealand Projections Projections Workshop 2004 Basic Projection Steps NZ Transverse Mercator Projections in ArcGIS 9.0 Reprojecting."— Presentation transcript:

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2 O LLIVIER & C O New Zealand Projections Projections Workshop 2004 Basic Projection Steps NZ Transverse Mercator Projections in ArcGIS 9.0 Reprojecting Images Discussion

3 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 The key is getting the datum transform working

4 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 new series (for identification) There is no easy or exact conversion 1949 2000 NZMG and 1949 circuits are same datum [GEO 1949] NZTM and 2000 circuits are same datum [NZGD2000] GPS coordinates are in WGS84 ~ NZGD2000

5 O LLIVIER & C O New Zealand Projections NZTopo50 - New Sheet Layouts New Zealand Transverse Mercator Metric Topographic Sheets 1:500 - 1:50,000 series Useful for NZTM Aerial photo tiles Not promoted by LINZ yet but coming….

6 O LLIVIER & C O New Zealand Projections Recognising the projection or datum Distinguish lat/long datum coords by 200 m offset North East (10,190) Distinguish projected coordinates by different false origins and ranges! X is always less than Y

7 O LLIVIER & C O New Zealand Projections NZTM Sheets & Names Similar concept to NZMG Portrait A1 1:50,000 base (prime rectangle) Corrected row x col numbering order 1:500 - 1:50,000 series height/width ratio 3:2

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

9 O LLIVIER & C O New Zealand Projections Why not? Do any layers have unknown coordinate systems? Are layers from different datums? If the datasets differ by thousands or millions of units *Usually the data is in completely different coordinate systems All projection parameter files are correct at ArcGIS 9.0 *Including North or South Island Yard Grids If two datasets are close ( < 200 metres ) *Usually different geographic coordinate systems (datums), or * WGS84 is not recognised as equivalent to NZGD2000, or *an approximate datum conversion is being used

10 O LLIVIER & C O New Zealand Projections Checking for layers with an unknown coordinate system A layer does not line up with the other layers Open Data Frame Properties Click Coordinate System tab...

11 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.

12 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 it works… 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

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

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

15 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 Projection and datum data is kept for file based images in the *.aux file. The world file is obsolete.

16 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 You cannot define NZGD2000 as a datum at 9.0 so NTv2 cannot be used to transform back to Geodetic

17 O LLIVIER & C O New Zealand Projections Does it work now? NO Research for more information: Did someone else use an approximate conversion? Data provider or source or age? Captured at different resolutions? 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.

18 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

19 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 if you want to use a transform or projection

20 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 approximately projected in ArcMap Has no defined transformations, uses a sphere Just as bad as no projection in practice Likely to occur in GPS data from other software Never leave the datum undefined for lat/long layers

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

22 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

23 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

24 O LLIVIER & C O New Zealand Projections NameLINZ parameters New_Zealand_1949_To_NZGD_2000_1_3PAR 54.4 -20.1 183.1 New_Zealand_1949_To_NZGD_2000_2_7PAR -59.47 -5.04 187.44 -0.47 0.10 -1.024 -4.5993 New_Zealand_1949_To_NZGD_2000_3_NTv220km Distortion Grid TypeAccuracy 3 parameter5 metres 7 parameter4 metres Distortion Grid0.2 metres If your data is at a resolution of less than the accuracy of the transform, then its nearly OK ArcGIS Datum Transformation Parameter Files

25 O LLIVIER & C O New Zealand Projections 7 Parameter coverage conversion example /* nzmg_nztm7.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 WGS84 SEVEN parameters 0.9996 173 00 00 00 00 00 1600000 10000000 end ArcInfo Projection Files

26 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. User group download script. 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.

27 O LLIVIER & C O New Zealand Projections Rearrange the parameter lists Re-arrange the coordinate folders to make them easier to find, move all the others to an Other. Different parameter conventions between ArcInfo & ArcGIS, especially conversion units for yards

28 O LLIVIER & C O New Zealand Projections ArcIMS Can set a datum manually in AXL See Australian Spatial newsletter

29 O LLIVIER & C O New Zealand Projections Reprojecting Images - a key barrier to change All new images will default to NZTM (photo control) Converting old images is more difficult than vector, as last year’s paper by Dave Horry Tiled images have to be merged with adjacent sheets Resampling degrades colours and resolution No quality assurance on the results Just reproject the world file??

30 O LLIVIER & C O New Zealand Projections Discussion FAQ at www.ollivier.co.nz/projection