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71 lines
2.3 KiB
71 lines
2.3 KiB
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shpproj |
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using the projection tools proj and invproj |
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we have implemented a shapefile projection utility |
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shpproj shp_file new_shp ( -i=in_proj_file | -i="in_params" | -i=geographic ) ( -o=out_info_file | -o="out_params" | -o=geographic ) |
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INPUT |
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Input can come from one of three sources. A projection parameter file, |
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directly through parameters or geographic. If the shapefile has an associated |
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prj file, name the same as the shapefile but ending in ".prj" it will be used |
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by default ignoring all other parameters. If input is omitted it defaults to |
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geographic, unless the default prj file exists.. |
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OUTPUT |
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Output can come from one of three sources. A projection parameter file, |
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directly through parameters or geographic. If output is omitted it defaults |
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to geographic. |
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PROJECTION PARAMETER FILE |
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This file MUST end with the extension ".prj". It has the form of one |
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projection parameter per line. Parameters can be in any order. |
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PROJECTION PARAMETERS |
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Are the same as used by proj and invproj. |
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use proj -lP to see available projections |
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proj -lu to see available units |
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proj -le to see available ellipsoid |
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USAGE |
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the following example projects file rowtest to row3, moving data from Stateplane NAD83 zone 1002 to utm zone 16 in meters |
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shpproj rowtest row -i="init=nad83:1002 units=us-ft" -o="proj=utm zone=16 units=m" |
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shpproj rowtest row3 -o="proj=utm zone=18 units=m" -i="zone=16 proj=utm units=us-ft" |
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shpproj rowtest row3 -o="proj=utm zone=18 units=m" |
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shpproj rowtest row3 -i=myfile.prj -o=geographic |
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shpproj rowtest row3 -is=myfile.prj |
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Datums |
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Stateplane data can be accessed by the init function |
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init=nad83:1003 |
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which is of the form |
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datum:FIPSzone |
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To move from NAD27 to NAD83 or otherwise the shpproj utility moves to |
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geographic coordinates and the back to the desired datum. proj can handle |
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direct datum to datum conversions but it is umimplemented here. |
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for a complete listing of FIPSZones by datum read nad/nad.lst in the PROJ4 |
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library |
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CAUTION |
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It is possible to get very poor results for projection values when using |
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coordinates VERY far away from the intended scope of the projection. |
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An example of a poor projection choice would be to move from nad83:1002 |
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(Georgia West) for data in California into utm. The resulting data will be |
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much less accurate than if it had started as geographic. |
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