Back To Week 7 and Feature-level Data
Preparation | On to Week 9 and Arc Macro Language
Back To Week 7 and Feature-level Data
Preparation | On to Week 9 and Arc Macro Language
Overview:
Projection & Coordinate System
A projection is a mathematical model that takes coordinate data which are on a curved surface (the earth) and converts the data to Cartesian coordinates on a flat surface. Projections are necessary in placing geographic data on flat map sheets or 2-dimensional computer models.
A coordinate system references every place on the map plane with an easting (x-coordinate) and a northing (y-coordinate).
Data are complicated mathematical models which describe the shape of the earth (because the earth is not a perfect sphere).
The spatial data for your portfolio all need to be in a common map projection and coordinate system, on a common datum. For the sake of UVIEW, we choose to use the Universal Transverse Mercator (UTM) projection and coordinate system.
The Universal Transverse Mercator (UTM) projection is used to define horizontal, positions world-wide by dividing the surface of the Earth into 6 degree zones, each mapped by the Transverse Mercator projection with a central meridian in the center of the zone. UTM zone numbers designate 6 degree longitudinal strips extending from 80 degrees South latitude to 84 degrees North latitude. UTM zone characters designate 8 degree zones extending north and south from the equator.
Eastings are measured from the central meridian (with a 500km false easting to insure positive coordinates). Northings are measured from the equator (with a 10,000km false northing for positions south of the equator).
If your data are in a projection and coordinate system other than UTM, you will have to project the data before exporting. Please review the on-line documentation regarding the Arc PROJECT command.
Your data will most likely come in one of only a few projections and coordinate systems. The most common are geographic (technically unprojected), State Plane (also a combination of projection and coordinate), and UTM.
To list your data's projection and coordinate description, use the DESCRIBE command:
Usage: DESCRIBE <geo_dataset>
Arc: describe bnd4
Description of DOUBLE precision coverage bnd4
FEATURE CLASSES
Number of Attribute Spatial
Feature Class Subclass Features data (bytes) Index? Topology?
------------- -------- --------- ------------ ------- ---------
ARCS 49 92
POLYGONS 4 86 Yes
NODES 48 12
SECONDARY FEATURES
Tics 36
Arc Segments 678
Polygon Labels 3
TOLERANCES
Fuzzy = 1.157 V Dangle = 0.000 N
COVERAGE BOUNDARY
Xmin = 1181905.875 Xmax = 1203109.000
Ymin = 544661.250 Ymax = 562044.438
STATUS
The coverage has not been Edited since the last BUILD or CLEAN.
COORDINATE SYSTEM DESCRIPTION
Projection STATEPLANE
Zone 5626
Datum HPGN
Units FEET Spheroid GRS1980
Parameters:
This description shows that the coverage bnd4 is in State Plane projection & coordinate system, zone 10, horizontal datum HPGN (High-Precision GPS Network), spheroid GRS1980, and units feet.
If your data do not list coordinate system parameters, you will need to contact the source for your data and find out what the details are before you continue.
Arc: describe streams
Description of DOUBLE precision coverage streams
FEATURE CLASSES
Number of Attribute Spatial
Feature Class Subclass Features data (bytes) Index? Topology?
------------- -------- --------- ------------ ------- ---------
ARCS 698 194 Yes
NODES 630 12
ANNOTATIONS (blank) 0
LARGE 60
SMALL 60
HUGE 61
SECONDARY FEATURES
Tics 12
Arc Segments 12322
TOLERANCES
Fuzzy = 1.157 N Dangle = 0.000 N
COVERAGE BOUNDARY
Xmin = 1178242.375 Xmax = 1206271.375
Ymin = 541386.563 Ymax = 564516.563
STATUS
The coverage has not been Edited since the last BUILD or CLEAN.
NO COORDINATE SYSTEM DEFINED
If you know the coordinate system parameters, but the data set's description does not include the parameters, you can add them using PROJECTDEFINE.
Usage: PROJECTDEFINE <COVER | GRID | FILE | TIN> <target> Arc: projectdefine cover streams Define Projection Project: projection state Project: zone 5626 Project: units feet Project: datum hpgn Project: parameters
Once the data set has its coordinate system defined, you can project it to another system using PROJECT.
Arc: project cover streams stream_utm ************************************************** * The INPUT projection has been defined. * ************************************************** Use OUTPUT to define the output projection and END to finish. Project: output Project: projection utm Project: zone 10 Project: units meters Project: datum nad27 Project: parameters Project: end Warning: By selecting STATEPLANE as a projection, the datum will default to NAD27 if not specified.
Here is the coordinate description of the new coverage:
Arc: describe stream_utm
Description of DOUBLE precision coverage stream_utm
FEATURE CLASSES
Number of Attribute Spatial
Feature Class Subclass Features data (bytes) Index? Topology?
------------- -------- --------- ------------ ------- ---------
ARCS 698 194
NODES 630 12
ANNOTATIONS (blank) 0
LARGE 60
SMALL 60
HUGE 61
SECONDARY FEATURES
Tics 12
Arc Segments 12322
TOLERANCES
Fuzzy = 0.853 N Dangle = 0.000 N
COVERAGE BOUNDARY
Xmin = 549889.175 Xmax = 558423.510
Ymin = 5182873.992 Ymax = 5190390.995
STATUS
The coverage has not been Edited since the last BUILD or CLEAN.
COORDINATE SYSTEM DESCRIPTION
Projection UTM
Zone 10
Datum NAD27
Units METERS Spheroid CLARKE1866
Parameters:
You can project coverages coverages and grids in this way. You can also project ASCII files as long as they are in the format:
x1, y1 x2, y2 ... xn, yn
MOSS files are used to create the spatial Paradox databases in UVIEW. The MOSS files need to represent either point, line, or polygon data. Use the ARCMOSS command to create MOSS files from coverages.
Usage: ARCMOSS <in_cover> <out_moss_file> <UTM | LATLONG> {attribute_item}
{lookup_table} {POLY | LINE | POINT}
You will need to choose either UTM or LATLONG output type. This controls the output data format.
The UTM option creates an export file using the absolute values of the coordinates written with a 2F11.2 format, while LATLONG causes coordinates to be written using a 2F10.5 format with negative longitude values.
You should also use the {attribute_item} option to place attribute values in the MOSS file. These values, such as stand name or stream type, will allow UVIEW to display your data in different colors, based on the attribute value. The {lookup_table} uses standard ARC/INFO lookup tables for related attribute values. You will also need to specify coverage data type if you are exporting anything other than a polygon coverage.
For example, ARCMOSS the forest stands coverage with the age in 1998:
Arc: arcmoss tty4 timbr_98.mos utm age_1998
or the streams coverage with the DNR type:
Arc: arcmoss str13_utm stream.mos utm str2dnrty # line
In order to display landscape views in UVIEW, you will need to generate a USGS-format digital elevation model (DEM). If you have used Grid commands and functions to create an elevation grid whose extent is your study area, you can export this. Otherwise, you can simply use a USGS DEM which you have downloaded from the UW GIS Data Archive or from the USGS.
The command to create a USGS-format DEM is simple:
Usage: LATTICEDEM <in_lattice> <out_dem> {z_factor} {FLOAT | INT}
You can apply an optional z-factor if you want to apply a constant multiplier to the output values. Also, you can specify integer output, if your data represent a surface with integer values. An integer DEM will be smaller than a floating-point DEM.
In general, you only need to export tabular data from ARC/INFO to the extent that the data are necessary in LMS. This probably only includes inventory data that may be stored as part of the forest stands coverage.
Several commands exist to dump out tables from the proprietary INFO format to a more widely used format, such as dBase delimited ASCII text. Here is a brief overview of the commands, the modules in which they are used, and the advantages and disadvantages of each command.
| OUTPUT, PRINT | INFO | ASCII | very precise | difficult to use |
| UNLOAD | Tables | ASCII | easy to use | does not include item name headers |
| INFODBASE | Arc | dBase IV | easy to use; maintains item definitions | truncates item names to 10 characters; changes item names |
| csv.aml | Arc | ASCII | easy to use | contains OS dependencies |
The INFO commands OUTPUT and PRINT place output in an ASCII file. However, these commands should be placed in an AML, because of the complexity of the commands.
UNLOAD, available in Tables, is very easy to use, but it does not output item names as a header. You will end up with a delimited or columnar ASCII file, but you will not know what the columns of data represent.
INFODBASE is very handy, especially because dBase files can be imported
directly to other applications, such as Excel and Access. However, although
it maintains item definitions, INFODBASE does not maintain the same item
naming convention as does INFO. Item names are truncated to 10 characters.
Any item names that are duplicates the same within the first 10 characters
will result in only the first item being exported. Also, any item names
with "-" or "." characters
will have these characters substituted with "_".
I have written an AML for converting any INFO table to a comma-delimited ASCII file (csv.aml). It has been formatted to run under UNIX (SunOS) or NT. It simply creates a comma-delimited ASCII file, just like the UNLOAD command, but it includes item name headers. The AML is easy to use, but it does not allow you to specify which items to dump; it exports the entire table.
Create a set of output files for import into LMS. These should all be in UTM projection (units meters, zone 10, datum NAD83):
MOSS files:
Pack Forest Boundary (bnd4)
Forest Stands with stand name as attribute item
Roads (no trails) with road surface type as attribute item
Streams with DNR type as attribute itemUSGS-format DEM for Pack Forest
Comma-separated ASCII file of the forest stand cover (tty4) PAT
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