Make your own free website on Tripod.com
GIS Developer
Navigation:
 Main Page
 
GIS Tools:
 AVPython
 NTXShape
 SHPTRANS
 
Other Tools:
 SciTE
 
Background:
 About Me

SHPTRANS: Shapefile Coordinate Transformation Utility

SHPTRANS is a high-precision, ultra-high-performance NTv2 datum transformation and projection utility which reads and writes shapefiles. SHPTRANS is intended to complement, not replace, existing projection tools such as those within ArcView GIS 3.x and ArcGIS 8.x.

Datum Support: SHPTRANS supports three datums / spheroids: NAD83 (GRS 1980 / WGS 1984), NAD27(Clarke 1866), and ATS77 (roughly, WGS 1972). If you want to transform between datums (the main purpose of SHPTRANS), a grid-shift file is required in NTv2 format. The Canadian NTv2 grid-shift file, used to transform between NAD27 and NAD83, is available for purchase from Natural Resources Canada. ESRI Canada has an agreement with NRCan, so that ESRI customers may obtain the grid-shift file for free.

There is a grid-shift file to transform between ATS77 and NAD83 for Atlantic Canada. This may be available from Nova Scotia Geomatics Centre, although I couldn't find it online. A much more detailed ATS77<->NAD83 grid-shift file covering only the province of New Brunswick is available from Service New Brunswick as part of NBGeoCalc. An updated grid-shift file is also available for PEI, and I understand the Nova Scotia high-res gridshift file is in the works.

If you have both the NAD27-NAD83 grid-shift file and an appropriate ATS77-NAD83 grid shift for your study area, SHPTRANS will convert in either direction between all three datums. If you have neither grid-shift file, you will not be able to convert between datums, but you can still use SHPTRANS to reproject without changing the datum.

Projection Support: SHPTRANS supports the following projections: UTM (tested for North America; intended to support all 60 zones in both hemispheres), MTM 3-degree (tested for Atlantic Canada; intended to also support Quebec), and New Brunswick and PEI Double Stereographic. The input and output coordinate system can be any of these projections, or lat/long decimal degrees. If a projection is specified, the map units are taken as metric (sorry, Americans).

This program was written for Windows NT, and should also run on other Win32 platforms. It includes a command line utility for use in batch conversions, and an ArcView 3.x extension to provide an interactive front-end. [DOWNLOAD]

Version 1.1 of the ArcView 3 extension did not work on newer versions of Windows (ME, 2000, and probably XP). Correcting this problem has been the focus of the 1.1a release. In the event that the ArcView extension is still broken on some OS, please try the command line version of the utility. The command line tool works on all known Win32 platforms.

ArcGIS 8.1 Projection Engine: ArcGIS 8.1 does not require SHPTRANS in order to perform NTv2 datum conversions. The NTv2 capability, and the Double Stereographic projection, have been integrated into the core ArcGIS projection engine. This means that ArcGIS can not only reproject ahead of time like SHPTRANS does (saving the result to a new file), but can also transform and project GIS layers on the fly.

SHPTRANS, the Future: So where does this leave SHPTRANS? ArcGIS's built in capabilities go far beyond what the old SHPTRANS GUI for ArcView could do, so that extension will never be ported to ArcGIS. However, SHPTRANS seems to be faster than ArcGIS at this point in time, and this makes it the best tool for converting a large amount of data in a batch job. Future work on the SHPTRANS command line tool might include having it use a .prj file if one is available, and on systems where ArcGIS is installed, it might integrate the projection engine to support a wider range of datums and projections.