EPSG code 6140 for NAD83/CSRS GeogGeodeticDatumGeoKey?

Martin Isenburg

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Dec 5, 2016, 10:06:49 AM12/5/16

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Hello,

a client is requesting for LAStools to support one seemingly missing value for the GeoTIFF tag GeogGeodeticDatumGeoKey that is currently not implemented. Here is the "meaning" of GeographicTypeGeoKey.

https://trac.osgeo.org/geotiff/browser/trunk/geotiff/html/spec/geotiff6.html?rev=448#L390

The value 6140 seems to refer to a Datum that is Ellispoid only in the definition files and therefore not listed.

What are the correct codes for the NAD83 (CSRS) datum? It seems the listed GeoTIFF codes do not cover the current values and do not have an entry for NAD83 (CSRS). Is it different from NAD 83? The client states that EPSG 6140 is the code for the NAD83/CSRS datum according to https://epsg.io/6140-datum and it is a replacement of the previous NAD83 datum for Canadian region.

Here is what lasinfo currently reports:

variable length header record 1 of 3:

reserved 0

user ID 'LASF_Projection'

record ID 34735

length after header 136

description 'GeoTIFF GeoKeyDirectoryTag'

GeoKeyDirectoryTag version 1.1.0 number of keys 16

key 1024 tiff_tag_location 0 count 1 value_offset 1 - GTModelTypeGeoKey: ModelTypeProjected

key 1025 tiff_tag_location 0 count 1 value_offset 1 - GTRasterTypeGeoKey: RasterPixelIsArea

key 1026 tiff_tag_location 34737 count 27 value_offset 0 - GTCitationGeoKey: NAD83(CSRS) / UTM zone 20N

key 2048 tiff_tag_location 0 count 1 value_offset 4140 - GeographicTypeGeoKey: look-up for 4140 not implemented

key 2049 tiff_tag_location 34737 count 14 value_offset 27 - GeogCitationGeoKey: NAD83(CSRS98)

key 2050 tiff_tag_location 0 count 1 value_offset 6140 - GeogGeodeticDatumGeoKey: look-up for 6140 not implemented

key 2052 tiff_tag_location 0 count 1 value_offset 9001 - GeogLinearUnitsGeoKey: Linear_Meter

key 2054 tiff_tag_location 0 count 1 value_offset 9102 - GeogAngularUnitsGeoKey: Angular_Degree

key 2056 tiff_tag_location 0 count 1 value_offset 7019 - GeogEllipsoidGeoKey: Ellipse_GRS_1980

key 2057 tiff_tag_location 34736 count 1 value_offset 1 - GeogSemiMajorAxisGeoKey: 6378137

key 2058 tiff_tag_location 34736 count 1 value_offset 2 - GeogSemiMinorAxisGeoKey: 6356752.314

key 2059 tiff_tag_location 34736 count 1 value_offset 0 - GeogInvFlatteningGeoKey: 298.2572221

key 3072 tiff_tag_location 0 count 1 value_offset 2961 - ProjectedCSTypeGeoKey: NAD83(CSRS) / UTM zone 20N

key 3073 tiff_tag_location 34737 count 27 value_offset 41 - PCSCitationGeoKey: NAD83(CSRS) / UTM zone 20N

key 3074 tiff_tag_location 0 count 1 value_offset 16020 - ProjectionGeoKey: look-up for 16020 not implemented

key 3076 tiff_tag_location 0 count 1 value_offset 9001 - ProjLinearUnitsGeoKey: Linear_Meter

Regards from Costa Rica,

Martin @rapidlasso

Kirk Waters - NOAA Federal

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Dec 5, 2016, 1:37:57 PM12/5/16

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Try using www.epsg-registry.org. For NAD83 (CSRS) with ellipsoid heights (i.e. the 3D coord system) the EPSG code is 4955. For the horizontal only (2D) it's 4617.

Kirk Waters, PhD | NOAA Office for Coastal Management

Applied Sciences Program | 2234 South Hobson Ave
843-740-1227 | Charleston, SC 29405

coast.noaa.gov/digitalcoast

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Evon Silvia

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Dec 5, 2016, 1:38:55 PM12/5/16

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According to the EPSG registry, EPSG code 6140 is the NAD83 Geodetic Datum (GeogGeodeticDatumGeoKey) as implemented in Canada and known as NAD83(CSRS).

Its derivative geographic coordinate systems are 4617 (2D) and 4955 (3D).

Using 4617 as the base, the derivative projected UTM coordinate systems in Canada are 3154-3157 (UTM7-10N), 2955-2957 (UTM11-13N), 3158-3160 (UTM14-16N), 2958-2962 (UTM17-21N), 3761 (UTM22N).

There's more than just that, but that should about cover it for most people. CompoundCRS definitions with CGVD2013 also exist.

Evon

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Michael Perdue

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Dec 6, 2016, 5:28:51 PM12/6/16

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Hello,

A quick word of discretion for users of epsg NAD83CSRS codes…

IMHO the EPSG database has poor support for NAD83CSRS. The geodetic datum entry for 6140 explicitly defines the epoch of realization for this datum as 1998. The problem is that I don’t know of any official entities that use that realization. The most common realizations are epoch’s 1997, 2002 and 2010; none of which are found anywhere in the EPSG registry. Admittedly, the horizontal differences between these realizations are small and inconsequential for most users, but the vertical component can be meaningful as some parts of Canada are experiencing significant post-glacial rebound (Hudson Bay) and/or tectonic upheaval (St. Elias range). Since the new vertical datum (CGVD2013) is a gravimetric datum rather than being based on a levelling network (CGVD28), the epoch of realization becomes important. In some regions, the vertical difference between the 1997 and 2010 epochs is > 15cm.

This makes the SRS ambiguous whenever NAD83(CSRS) is referenced. You also need the epoch of realization in order to remove the ambiguity. Unfortunately, I don’t know of a better option. The situation is even worse for WGS84, which has at least 6 different realizations that I'm aware of, but uses the same geodetic datum entry for all (6326).

Cheers,

Mike

Sent from my iPad

Jean-François Bourgon

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Jan 6, 2017, 10:37:54 AM1/6/17

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I would suggest adding native support for following frequent projection definitions:

https://epsg.io/4617 - NAD83(CSRS) / Geodetic2D

https://epsg.io/2945 - NAD83(CSRS) / MTM zone 3

https://epsg.io/2946 - NAD83(CSRS) / MTM zone 4

https://epsg.io/2947 - NAD83(CSRS) / MTM zone 5

https://epsg.io/2948 - NAD83(CSRS) / MTM zone 6

https://epsg.io/2949 - NAD83(CSRS) / MTM zone 7

https://epsg.io/2950 - NAD83(CSRS) / MTM zone 8

https://epsg.io/2951 - NAD83(CSRS) / MTM zone 9

https://epsg.io/2952 - NAD83(CSRS) / MTM zone 10

https://epsg.io/2953 - NAD83(CSRS) / New Brunswick Stereographic

https://epsg.io/2954 - NAD83(CSRS) / Prince Edward Isl. Stereographic

https://epsg.io/2955 - NAD83(CSRS) / UTM zone 11N

https://epsg.io/2956 - NAD83(CSRS) / UTM zone 12N

https://epsg.io/2957 - NAD83(CSRS) / UTM zone 13N

https://epsg.io/2958 - NAD83(CSRS) / UTM zone 17N

https://epsg.io/2959 - NAD83(CSRS) / UTM zone 18N

https://epsg.io/2960 - NAD83(CSRS) / UTM zone 19N

https://epsg.io/2961 - NAD83(CSRS) / UTM zone 20N

https://epsg.io/2962 - NAD83(CSRS) / UTM zone 21N

https://epsg.io/3153 - NAD83(CSRS) / BC Albers

https://epsg.io/3154 - NAD83(CSRS) / UTM zone 7N

https://epsg.io/3155 - NAD83(CSRS) / UTM zone 8N

https://epsg.io/3156 - NAD83(CSRS) / UTM zone 9N

https://epsg.io/3157 - NAD83(CSRS) / UTM zone 10N

https://epsg.io/3158 - NAD83(CSRS) / UTM zone 14N

https://epsg.io/3159 - NAD83(CSRS) / UTM zone 15N

https://epsg.io/3160 - NAD83(CSRS) / UTM zone 16N

https://epsg.io/3761 - NAD83(CSRS) / UTM zone 22N

https://epsg.io/3979 - NAD83(CSRS) / Canada Atlas Lambert

J-F

Jeff McKenna

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Jan 6, 2017, 11:26:30 AM1/6/17

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On 2017-01-06 10:34 AM, Jean-François Bourgon wrote:
>
> https://epsg.io/3979 - NAD83(CSRS) / Canada Atlas Lambert
>

Happy to see 3979 floating around finally: this was filed by me back in
2009 to the EPSG geodetic group, for acceptance :)

-jeff

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Perdue, Michael

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Jan 6, 2017, 12:59:56 PM1/6/17

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Hi,

These are all supported by lastools already and have been for some time.

The only exception are 2953 and 2954. AFAIK, LAStools does not support Stereographic projections at this time. As a result, you can embed projection information into the file for those two CRS, but you can’t re-project your data from/to 2953/2954.

Cheers,

Mike

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Martin Isenburg

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Jan 8, 2017, 2:39:29 PM1/8/17

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Hello,

the missing implementation was mostly in the lasinfo textual output that did not recognize all fields. As of LAStools version 170108 it does that all properly (I hope). Please check the generated OGC WKT string below.

>> las2las -i 0245070064160_2013_ALLHITS_utm_20N.las ^

-set_ogc_wkt ^

-odix _new -olaz

>>lasinfo -i 0245070064160_2013_ALLHITS_utm_20N_new.laz

lasinfo (170108) report for 0245070064160_2013_ALLHITS_utm_20N_new.laz

reporting all LAS header entries:

file signature: 'LASF'

file source ID: 0

global_encoding: 0

project ID GUID data 1-4: 00000000-0000-0000-EA00-50B89D0B2E3A

version major.minor: 1.2

system identifier: 'LAStools (c) by rapidlasso GmbH'

generating software: 'las2las (version 170108)'

file creation day/year: 155/2013

header size: 227

offset to point data: 1314

number var. length records: 4

point data format: 1

point data record length: 28

number of point records: 1723759

number of points by return: 1497942 127539 63600 25703 7329

scale factor x y z: 0.0001 0.0001 0.0001

offset x y z: 408013.951 4992001.7916999999 0

min x y z: 407091.2989 4991361.0830 -42.4459

max x y z: 408701.3410 4992512.9457 1061.7390

variable length header record 1 of 4:

reserved 0

user ID 'LASF_Projection'

record ID 34735

length after header 136

description 'GeoTIFF GeoKeyDirectoryTag'

GeoKeyDirectoryTag version 1.1.0 number of keys 16

key 1024 tiff_tag_location 0 count 1 value_offset 1 - GTModelTypeGeoKey: ModelTypeProjected

key 1025 tiff_tag_location 0 count 1 value_offset 1 - GTRasterTypeGeoKey: RasterPixelIsArea

key 1026 tiff_tag_location 34737 count 27 value_offset 0 - GTCitationGeoKey: NAD83(CSRS) / UTM zone 20N

key 2048 tiff_tag_location 0 count 1 value_offset 4140 - GeographicTypeGeoKey: GCSE_NAD83_CSRS

key 2049 tiff_tag_location 34737 count 14 value_offset 27 - GeogCitationGeoKey: NAD83(CSRS98)

key 2050 tiff_tag_location 0 count 1 value_offset 6140 - GeogGeodeticDatumGeoKey: Datum_NAD83_CSRS