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Diffstat (limited to 'docs/source/usage/transformation.rst')
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1 files changed, 8 insertions, 8 deletions
diff --git a/docs/source/usage/transformation.rst b/docs/source/usage/transformation.rst index fd1f2f94..bd32bcd9 100644 --- a/docs/source/usage/transformation.rst +++ b/docs/source/usage/transformation.rst @@ -6,11 +6,11 @@ Geodetic transformation PROJ can do everything from the most simple projection to very complex transformations across many reference frames. While originally developed as a -tool for cartographic projections, PROJ has over time evolved into a powerfull +tool for cartographic projections, PROJ has over time evolved into a powerful generic coordinate transformation engine that makes it possible to do both large scale cartographic projections as well as coordinate transformation at a geodetic high precision level. This chapter delves into the details of how -geodetec transformations of varying complexity can be performed. +geodetic transformations of varying complexity can be performed. In PROJ, two frameworks for geodetic transformations exists, the *cs2cs* framework and the *transformation pipelines* framework. The first is the original, @@ -69,7 +69,7 @@ solutions for a wide spectrum of geodetic tasks. As a first example, let us take a look at the iconic *geodetic → Cartesian → Helmert → geodetic* case (steps 2 to 4 in the example in -the itroduction). In PROJ it can be implemented as +the introduction). In PROJ it can be implemented as :: @@ -161,11 +161,11 @@ specified in the input proj-string. The most common is ``+towgs84``, which is us define a 3- or 7-parameter Helmert shift from the input reference frame to WGS84. Exactly which realization of WGS84 is not specified, hence a fair amount of uncertainty is introduced in this step of the transformation. With the +nadgrids -parameter a non-lineaer planar correction derived from interpolation in a +parameter a non-linear planar correction derived from interpolation in a correction grid can be applied. Originally this was implemented as a means to -transform coordinates between the american datums NAD27 and NAD83, but corrections -can be applied for any datum for which a correction grid exists. The inverse -transform for the horizontal grid shift is "dumb", in the sense that the +transform coordinates between the North American datums NAD27 and NAD83, but +corrections can be applied for any datum for which a correction grid exists. The +inverse transform for the horizontal grid shift is "dumb", in the sense that the correction grid is applied verbatim without taking into account that the inverse operation is non-linear. Similar to the horizontal grid correction, ``+geoidgrids`` can be used to perform grid corrections in the vertical component. @@ -203,7 +203,7 @@ using an approximated 7 parameter transformation. Grid Based Datum Adjustments +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -In many places (notably North America and Austrialia) national geodetic +In many places (notably North America and Australia) national geodetic organizations provide grid shift files for converting between different datums, such as NAD27 to NAD83. These grid shift files include a shift to be applied at each grid location. Actually grid shifts are normally computed based on an |