# Resource files¶

A number of files containing preconfigured transformations and default parameters for certain projections are bundled with the PROJ distribution. Init files contains preconfigured proj-strings for various coordinate reference systems and the defaults file contains default values for parameters of select projections.

In addition to the bundled init-files the PROJ.4 project also distribute a number of packages containing transformation grids and additional init-files not included in the main PROJ package.

## External resources¶

For a functioning PROJ installation of the proj-datumgrid is needed. If you have installed PROJ from a package system chances are that this will already be done for you. The proj-datumgrid package provides transformation grids that are essential for many of the predefined transformations in PROJ. Which grids are included in the package can be seen on the proj-datumgrid repository as well as descriptions of those grids.

In addition to the default proj-datumgrid package regional packages are also distributed. These include grids and init-files that are valid within the given region. The packages are divided into geographical regions in order to keep the needed disk space by PROJ at a minimum. Some users may have a use for resource files covering several regions in which case they can download more than one.

At the moment three regional resource file packages are distributed:

## Transformation grids¶

Grid files are important for shifting and transforming between datums.

PROJ supports CTable2, NTv1 and NTv2 files for horizontal grid corrections and the GTX file format for vertical corrections. Details about the formats can be found in the GDAL documentation. GDAL reads and writes all formats. Using GDAL for construction of new grids is recommended.

Below is a given a list of grid resources for various countries which are not included in the grid distributions mentioned above.

### Free grids¶

#### Switzerland¶

Background in ticket #145

We basically have two shift grids available. An official here:

Swiss CHENyx06 dataset in NTv2 format

And a derived in a temporary location which is probably going to disappear soon.

Main problem seems to be there’s no mention of distributivity of the grid from the official website. It just tells: “you can use freely”. The “contact” link is also broken, but maybe someone could make a phone call to ask for rephrasing that.

#### Hungary¶

Hungarian grid ETRS89 - HD72/EOV (epsg:23700), both horizontal and elevation grids

### Non-Free Grids¶

Not all grid shift files have licensing that allows them to be freely distributed, but can be obtained by users through free and legal methods.

#### Austria¶

Austrian Grid for MGI

#### Brazil¶

Brazilian grids for datums Corrego Alegre 1961, Corrego Alegre 1970-72, SAD69 and SAD69(96)

#### Portugal¶

Portuguese grids for ED50, Lisbon 1890, Lisbon 1937 and Datum 73

#### South Africa¶

South African grid (Cape to Hartebeesthoek94 or WGS84)

#### Spain¶

Spanish grids for ED50.

### HARN¶

With the support of i-cubed, Frank Warmerdam has written tools to translate the HPGN grids from NOAA/NGS from .los/.las format into NTv2 format for convenient use with PROJ. This project included implementing a .los/.las reader for GDAL, and an NTv2 reader/writer. Also, a script to do the bulk translation was implemented in https://github.com/OSGeo/gdal/tree/trunk/gdal/swig/python/samples/loslas2ntv2.py. The command to do the translation was:

loslas2ntv2.py -auto *hpgn.los


As GDAL uses NAD83/WGS84 as a pivot datum, the sense of the HPGN datum shift offsets were negated to map from HPGN to NAD83 instead of the other way. The files can be used with PROJ like this:

cs2cs +proj=latlong +datum=NAD83

# input:
-112 34

# output:
111d59'59.996"W 34d0'0.006"N -0.000


This was confirmed against the NGS HPGN calculator.

### HTDP¶

This page documents use of the crs2crs2grid.py script and the HTDP (Horizontal Time Dependent Positioning) grid shift modelling program from NGS/NOAA to produce PROJ compatible grid shift files for fine grade conversions between various NAD83 epochs and WGS84. Traditionally PROJ has treated NAD83 and WGS84 as equivalent and failed to distinguish between different epochs or realizations of those datums. At the scales of much mapping this is adequate but as interest grows in high resolution imagery and other high resolution mapping this is inadequate. Also, as the North American crust drifts over time the displacement between NAD83 and WGS84 grows (more than one foot over the last two decades).

#### Getting and building HTDP¶

The HTDP modelling program is in written FORTRAN. The source and documentation can be found on the HTDP page at http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml

On linux systems it will be necessary to install gfortran or some FORTRAN compiler. For ubuntu something like the following should work.

apt-get install gfortran


To compile the program do something like the following to produce the binary “htdp” from the source code.

gfortran htdp.for -o htdp


#### Getting crs2crs2grid.py¶

The crs2crs2grid.py script can be found at https://github.com/OSGeo/gdal/tree/trunk/gdal/swig/python/samples/crs2crs2grid.py

It depends on having the GDAL Python bindings operational. If they are not

Traceback (most recent call last):
File "./crs2crs2grid.py", line 37, in <module>
from osgeo import gdal, gdal_array, osr
ImportError: No module named osgeo


#### Usage¶

   crs2crs2grid.py
<src_crs_id> <src_crs_date> <dst_crs_id> <dst_crs_year>
[-griddef <ul_lon> <ul_lat> <ll_lon> <ll_lat> <lon_count> <lat_count>]
[-htdp <path_to_exe>] [-wrkdir <dirpath>] [-kwf]
-o <output_grid_name>

-griddef: by default the following values for roughly the continental USA
at a six minute step size are used:
-127 50 -66 25 251 611
-kwf: keep working files in the working directory for review.

crs2crs2grid.py 29 2002.0 8 2002.0 -o nad83_2002.ct2


The goal of crs2crs2grid.py is to produce a grid shift file for a designated region. The region is defined using the -griddef switch. When missing a continental US region is used. The script creates a set of sample points for the grid definition, runs the “htdp” program against it and then parses the resulting points and computes a point by point shift to encode into the final grid shift file. By default it is assumed the htdp program will be in the executable path. If not, please provide the path to the executable using the -htdp switch.

The htdp program supports transformations between many CRSes and for each (or most?) of them you need to provide a date at which the CRS is fixed. The full set of CRS Ids available in the HTDP program are:

 1...NAD_83(2011) (North America tectonic plate fixed)

4...WGS_72                             16...ITRF92
6...WGS_84(G730) = ITRF92              18...ITRF94 = ITRF96
7...WGS_84(G873) = ITRF96              19...ITRF96
8...WGS_84(G1150) = ITRF2000           20...ITRF97
9...PNEOS_90 = ITRF90                  21...IGS97 = ITRF97
10...NEOS_90 = ITRF90                   22...ITRF2000
11...SIO/MIT_92 = ITRF91                23...IGS00 = ITRF2000
12...ITRF88                             24...IGb00 = ITRF2000
13...ITRF89                             25...ITRF2005
14...ITRF90                             26...IGS05 = ITRF2005
15...ITRF91                             27...ITRF2008
28...IGS08 = ITRF2008


The typical use case is mapping from NAD83 on a particular date to WGS84 on some date. In this case the source CRS Id “29” (NAD_83(CORS96)) and the destination CRS Id is “8 (WGS_84(G1150)). It is also necessary to select the source and destination date (epoch). For example:

crs2crs2grid.py 29 2002.0 8 2002.0 -o nad83_2002.ct2


The output is a CTable2 format grid shift file suitable for use with PROJ (4.8.0 or newer). It might be utilized something like:

cs2cs +proj=latlong +ellps=GRS80 +nadgrids=./nad83_2002.ct2 +to +proj=latlong +datum=WGS84


## Init files¶

Init files are used for preconfiguring proj-strings for often used transformations, such as those found in the EPSG database. Most init files contain transformations from a given coordinate reference system to WGS84. This makes it easy to transformations between any two coordinate reference systems with cs2cs. Init files can however contain any proj-string and don’t necessarily have to follow the cs2cs paradigm where WGS84 is used as a pivot datum. The ITRF init file is a good example of that.

A number of init files come pre-bundled with PROJ but it is also possible to add your own custom init files. PROJ looks for the init files in the directory listed in the PROJ_LIB environment variable.

The format of init files made up of a identifier in angled brackets and a proj-string:

<3819> +proj=longlat +ellps=bessel
+towgs84=595.48,121.69,515.35,4.115,-2.9383,0.853,-3.408 +no_defs <>


The above example is the first entry from the epsg init file. So, this is the coordinate reference system with ID 3819 in the EPSG database. Comments can be inserted by prefixing them with a “#”. With version 4.10.0 a new special metadata entry is now accepted in init files. It can be parsed with a function from the public API. The metadata entry in the epsg init file looks like this at the time of writing:

<metadata> +version=9.0.0 +origin=EPSG +lastupdate=2017-01-10


Pre-configured proj-strings from init files are used in the following way:

\$ cs2cs -v +proj=latlong +to +init=epsg:3819
# ---- From Coordinate System ----
#Lat/long (Geodetic alias)
#
# +proj=latlong +ellps=WGS84
# ---- To Coordinate System ----
#Lat/long (Geodetic alias)
#
# +init=epsg:3819 +proj=longlat +ellps=bessel
# +towgs84=595.48,121.69,515.35,4.115,-2.9383,0.853,-3.408 +no_defs


It is possible to override parameters when using +init. Just add the parameter to the proj-string alongside the +init parameter. For instance by overriding the ellipsoid as in the following example

+init=epsg:25832 +ellps=intl


where the Hayford ellipsoid is used instead of the predefined GRS80 ellipsoid. It is also possible to add additional parameters not specified in the init file, for instance by adding an observation epoch when transforming from ITRF2000 to ITRF2005:

+init=ITRF2000:ITRF2005 +t_obs=2010.5


which then expands to

+proj=helmert +x=-0.0001 +y=0.0008 +z=0.0058 +s=-0.0004
+dx=0.0002 +dy=-0.0001 +dz=0.0018 +ds=-0.000008
+t_epoch=2000.0 +convention=position_vector
+t_obs=2010.5


Below is a list of the init files that are packaged with PROJ.

Name Description
esri Auto-generated mapping from Esri projection index. Not maintained any more
epsg EPSG database
GL27 Great Lakes Grids
IGNF French coordinate systems supplied by the IGNF
ITRF2000 Full set of transformation parameters between ITRF2000 and other ITRF’s
ITRF2008 Full set of transformation parameters between ITRF2008 and other ITRF’s
ITRF2014 Full set of transformation parameters between ITRF2014 and other ITRF’s
nad27 State plane coordinate systems, North American Datum 1927
nad83 State plane coordinate systems, North American Datum 1983

## The defaults file¶

The proj_def.dat file supplies default parameters for PROJ. It uses the same syntax as the init files described above. The identifiers in the defaults file describe to what the parameters should apply. If the <general> identifier is used, then all parameters in that section applies for all proj-strings. Otherwise the identifier is connected to a specific projection. With the defaults file supplied with PROJ the default ellipsoid is set to WGS84 (for all proj-strings). Apart from that only the Albers Equal Area, Lambert Conic Conformal and the Lagrange projections have default parameters. Defaults can be ignored by adding the +no_def parameter to a proj-string.