ArcGIS tips

Choose your North Arrow wisely; it implies Magentic or True North.

Submitted by emarsh on Wed, 2009-02-25 11:35
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I always chose my north arrow based on style. However, my advisor reminded me to be more careful, as explained here: http://www.cavesurvey.com/north_arrows.htm

Basically, a north arrow with two sides indicates true north, while an arrow with one side indicates magnetic north. Choose wisely.

On a related topic, you can calculate the magnetic declination of your location here: http://www.ngdc.noaa.gov/geomag/

 

Workshop 2008 - Maps Linking GPS and Lab Results

in
Archaeological Research Facility at UC Berkeley
PRACTICAL WORKSHOP
Working with Archaeological survey data in Arcmap 9.2:
Making maps that link GPS point locations with artifact-level lab data
Friday Feb 22, 2008
N. Tripcevich
If images are absent in the webpage below, please Reload the webpage and allow it to load completely.

Data used in workshop:

The Effects of the Curvature of the Earth, the Refraction of Light in Air, and Fuzzy Viewsheds in ArcGIS 9.2

Submitted by emarsh on Sun, 2008-01-27 19:24
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In making viewshed calculations, the earth's curve and the refraction of light in air have an impact (albeit minor) on lines of sight. I this post, I provide some links describing how Arc calculates both variables. I would love to find out how to recalculate the "refractivity coefficient" of 0.13 to other situations. I also put a plug in for fuzzy viewsheds, a drastic improvement that was first suggested 15 years ago, to be mostly ignored in practice until very recently.

Corrections for the Curvature of the Earth

Finding the right transformation when re-projecting data in ArcGIS 9.2

Submitted by emarsh on Wed, 2008-01-16 22:45
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So you're using the Project Tool to re-projecting a map into a new projection.

Before you can start the process, you have to choose from the many transformations. The attached file (World Projections.xls) lists where in the world each projection transformation should be used.

For example, if your map is in PSAD56, and you want to project it to WGS84, the Project Tool will ask you which transformation you want. Checking the lists for Bolivia, I find: PSAD_1956_To_WGS_1984_2

Finding the right transformation when re-projecting data in ArcGIS 9.2

Submitted by emarsh on Wed, 2008-01-16 22:43
in

So you're using the Project Tool to re-projecting a map into a new projection.

Before you can start the process, you have to choose from the many transformations. The attached file (World Projections.xls) lists where in the world each projection transformation should be used.

For example, if your map is in PSAD56, and you want to project it to WGS84, the Project Tool will ask you which transformation you want. Checking the lists for Bolivia, I find: PSAD_1956_To_WGS_1984_2

 

Batch DEM -> GRID AML for ArcGRID

Submitted by nico on Sat, 2007-04-14 17:19
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When you get many small tiles of data from sources like
http://data.geocomm.com/catalog/index.html

(a source of 1:24,000 DEMs for the contiguous US states)

You often need to batch convert these files to a native ESRI format.

Here's an AML to run at the GRID command to convert all DEM files in the folder to GRID

Creating LZW compressed TIFF files outside of a Geodatabase

Submitted by nico on Fri, 2007-03-23 05:50
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generating a compressed GeoTIFF for ArcGIS that is outside of a Geodatabase

Software: ArcGIS 9.2, Adobe Photoshop

Question

Experimenting with raster compression formats with a scan of a ~D sized paper map (300 dpi) I found that after georeferencing (using Lat/Long) I could create a 18mb JPG file together with its JGW worldfile at about 80% JPG compression. How large would this file be in a non-lossy format that is widely readable by non-GIS users?

Setup Batch processing in ArcGIS 9.2 with Excel

Submitted by nico on Thu, 2007-02-22 08:52
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Setup Batch processing in ArcGIS 9.2 with Excel

With v9.2 ESRI has brought a useful batch processor to most of the toolbox functions.

Right-clicking the item in the toolbox view shows the "Batch..." command.

The matrix of cells that appear in the Batch command can be difficult to fill-in, however I've found that you can construct a more elaborate batch in MS Excel and then paste those values back in to the ArcGIS batch window.

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Cartographic transformations in ArcGIS for South America

Submitted by nico on Fri, 2006-11-03 11:10
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ArcGIS offers a number of geographic transformations between coordinates in the older Prov South American Datum of 1956 (PSAD56) and the modern WGS 1984 datum.

Finding the PSAD1956 datum in ArcGIS

The PSAD1956 datum is supported in ArcGIS. The coordinate system settings are found under Coordinate System menus under UTM (Universal Transverse Mercator)

Predefined > Projected Coordinates > UTM > Other GCS > Prov. S. Amer Datum, UTM Zone X (Northern or Southern hemisphere).

Vector-border Technique for Reprojecting Rasters

Submitted by nico on Wed, 2006-11-01 07:43
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Vector-border Technique for Reprojecting Rasters

Summary: This technique allows a user to bring scanned maps and other rasters from a variety of projections and coordinate systems into a common reference system. The idea is that a vector file can be transformed more easily than a raster file, so a vector border of a raster map is transformed (in lieu of the raster itself), and then the raster is re-georeferenced to the new vector position.

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