o llivier & c o new zealand projections projections workshop basic projection steps nz...
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OLLIVIER & CO New Zealand Projections
Projections Workshop
• Basic Projection Steps
• NZ Transverse Mercator
• Projections in ArcGIS 8.2
• Reprojecting Images
• Discussion
OLLIVIER & CO 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 Transformation3 or 7 parameter equationor Distortion Grid (NTv2)or None if same datum
Unproject
Project
Unproject
Project
OLLIVIER & CO 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
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 A1 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 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
OLLIVIER & CO 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
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 ArcCatalog• 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 ArcMap, 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 ArcMap• 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
Name LINZ 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_NTv2 20km Distortion Grid
Type Accuracy
3 parameter 5 metres
7 parameter 4 metres
Distortion Grid 0.2 metres
ArcGIS Datum Transformation Parameter Files
OLLIVIER & CO New Zealand Projections
7 Parameter conversion example
/* nzmg_nztm7.prj/* APPROXIMATE NZMG to NZTM (~4 metre error)input projection NEWZEALAND_GRIDunits metersdatum USER_DEFINED 59.47 -5.04 187.44 -0.47 0.10 -1.024 -4.5993parametersoutputprojection TRANSVERSEunits metersdatum WGS84 SEVENparameters0.9996173 00 0000 00 00160000010000000end
ArcInfo Projection Files
OLLIVIER & CO 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.
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 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.
OLLIVIER & CO New Zealand Projections
New Sheet Layouts
New Zealand Transverse Mercator
Metric Topographic Sheets
1:500 - 1:50,000 series
Aerial photographs
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