Tag: Grid

ArcGIS Pro Tips: Group Templates, Galleries, & Grids Make Editing a Snap

ArcGIS-Pro-Tips

ArcGIS Pro includes a wide variety of editing tools right out of the box. These interactive tools can be used to create, modify, or delete the features and related data on layers in 2D and 3D. You can use the … Continue reading

Posted in 3D GIS, ArcGIS Pro, Editing, Mapping, Uncategorized | Tagged , , , , , , , , , , | 1 Comment

Using Statistical Sampling with Positional Accuracy Assessment Tool

A common question when using Data Reviewer’s Positional Accuracy Assessment Tool (PAAT) is what sample size should be used when evaluating a geospatial data layer. Sometimes the sample size is mandated by a specification; but when it’s not, Data Reviewer’s Sampling check can be used to provide the sample size. In this blog, I’ll discuss how you can use the Sampling check to generate a statistically valid sample size and then explore two options for using it with the PAAT.

The steps include:

1. From the Data Reviewer toolbar, select the Select Data Check dropdown.

2. Expand the Advanced Checks category and select Sampling Check

3. In the Sampling Check Properties dialog, select Auto Calculate.


4. Under Auto Calculate, select your Confidence Level and Margin of Error.

Note: The question you’re looking to answer: given a population size (number of features), what sample size do I need so that I’m “X” percent confident the sample size is statistically significant within a “Y” percent margin of error?

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For those using Esri Grid

The Esri Grid format for storing raster data has been around for…well, longer than this writer has been doing GIS. But we keep learning about things that need to be added to the documentation.  I’m sure those original Grid users could probably tell me more than I ever wanted to know about the format, but here’s a limitation that was news to me.

The name of a Grid has certain limitations, but did you also know that there’s a limit to the number of Grids that can be stored in a workspace? The following lists the theoretical maximum number of Grid datasets that can be stored in a single workspace directory:

  • less than 5000 floating point Grids, or
  • less than 3333 integer Grids, with VATs (less than 5000 if no VATs), or
  • less than 10000 Grid stacks

The preceding numbers are the theoretical maximums. If you have a process that will create interim Grids (and therefore files in the INFO directory) these numbers will be less. Additionally, if you are storing a mix of files, such as Grids and coverages, you will store fewer.

These numbers relate to the number of files in the Grid folder that store information in the INFO directory. The limit is 10,000 (well, 9,999), but it’s not the total number of files in an INFO directory, it’s the number of files pointing to the files in the INFO directory. For each Grid, there are two files in the Grid’s folder pointing to files in the INFO folder: the BND (boundary) files, and STA table (statistics) files (9999/2?5000). When a Grid has a VAT, this also points to files in the INFO directory, so the number that can be stored is reduced again (9999/3?3333). A Grid stack only has a single file which points to the INFO directory (9999/1?9999).

You can get a count of the number of files in an INFO directory using Windows Explorer.

  1. Navigate to the INFO directory.
  2. Select all the *.dat files (each Grid file points to a .nit and a .dat file).
  3. Right-click and select Properties.

This will give you the count of files. Regardless of the data is in the directory (Grids, stacks, coverages, etc.), when that number gets to 9999, the INFO directory is full and you’ll get an error message to the effect of: “Fatal Error: (INFDEF) directory full”. If you happen to come across this limit, you can either create a new workspace to work in, or remove any data that is no longer needed.

Melanie Harlow

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Converting and Displaying Coordinates in ArcGIS 10

There are many ways of representing locations.  One of the most common uses angular latitude and longitude coordinates to specify the location of a point.  These Geographic coordinates may be expressed in several different notations, including Decimal Degrees (DD), Degrees Decimal Minutes (DDM), and Degrees Minutes and Seconds (DMS). The formula for converting Degree Minutes and Seconds to Decimal Degrees is discussed in the ArcGIS 10 Help.  Another common method is to use a projected coordinate system and X and Y coordinate pairs, that is, two sets of numbers in a planar Cartesian system.

Gridded systems, like Universal Transverse Mercator (UTM), United States National Grid (USNG), Military Grid Reference System (MGRS) divide the world into zones which are projected and then overlaid with one or more grids.  Within the grids, point locations are specified by their position East and North the zone origin or the southeast corner of the cell. For USNG and MGRS the numeric values of the northing and easting can vary from 1 to 5 digits, depending on the precision of the location (they must both use the same number of digits) and then the values are concatenated.

Two less frequently used systems, the Global Area Reference System (GARS) and Geographic Reference System (GEOREF), divide the world into polygonal areas based on different sets of nested grids and encode locations as a string of grid ID values.

Philadelphia coordinatesEach of these ways of representing a location results in different strings of characters with a variety of formats.  This table shows the coordinate representation for Philadelphia, Pennsylvania in the US (75° 9’ 18.382” West longitude by 39° 59’ 0.637” North latitude) in each of these systems.  This is not an exhaustive list of the delimiters and hemisphere indicators that are used in each system.

ArcGIS 10 can convert coordinates expressed in each of these systems into the others, and provides ways of displaying and accepting coordinate input in most of them.

Displaying Coordinates

Status bar coordinate displayYou can see the coordinate value for a place on a map in the ArcMap status bar, at the bottom right of the application. The default coordinate format in the status bar is based on the units of the first layer added to the map, often feet, meters, or degrees of longitude/latitude.

Status bar showing MGRS

 

You can change the coordinate display to use any of these systems (except GARS and GEOREF) by right-clicking Layers in the table of contents and selecting Properties. On the General tab, under Units, you can select the type of coordinates you would like to see, for example MGRS.

Go To XY Coordinates

Go To XY tool locationIf you have a set of coordinates and you want to find their location on the map, you can use the Go To XY tool. Go To XY tool dialog box

 

 

Open the tool from the toolbar, then select a coordinate format. Type (or paste) the coordinates into the text box and click one of the buttons to Pan to, Zoom to, Flash, Add a Point, Add a Point Labeled with Coordinates, or Add a Callout.

The Go To XY tool also keeps a record of recent locations, which you can return to by clicking the Recent button and selecting the location. You can use this to manually convert coordinates from one format to another. To do so, select your input coordinate notation, input your coordinates and pan to the location. Then select your new output format and select the coordinates from the Recent button.

Find MGRS coordinates

Find tool locationsIf you work with MGRS coordinates, the Find tool has an MGRS Locator that works like the Go To XY tool, but provides additional capabilities tailored to the MGRS system.

Find tool dialog box

 

 

To use these, open the Find tool on the Tools toolbar.  In the Find tool dialog box, click the Locations tab, select MGRS from the locator drop-down list.  Then type (or paste) the coordinate into the MGRS box and click Find.

Find tool options

 

 

 

 

The tool will return a list of location matches (in our case there should only be one). If you right-click on the coordinate you have various options for marking the location.

So what’s different about the MGRS Locator?

The locator has options for matching shortened MGRS coordinates when you work in the same Grid Zone Designator (GZD).  It has options to pull the GZD and 100,000 meter square identifier from the current map center, a default value, or use the last one used. This is convenient if you work in the same GZD over and over again, you can type “8675725939” or “VK8675725939” rather than “18SVK8675725939”, which will save you a few extra key strokes when entering your coordinates.

Converting Tables of Coordinates

Table of coordinatesThere may be times when you have a lot of coordinates that you need to convert to another system.  If you have the coordinates in a table, you can convert all of them by running the Convert Coordinate Notation (CCN) geoprocessing tool. 

For example, you might convert a table of longitude and latitude values in decimal degrees (DD) to MGRS.

 

CCN tool dialog

 

With the CCN tool you can convert between DD, DDM, DMS, UTM, USNG, MGRS, GARS, and GEOREF.

The tool takes your table of coordinates and converts them to point features with an attribute containing the new output notation.

It is important to note that the CCN tool is a geoprocessing tool and represents a single-focus process of converting a table of coordinates; its only function is to do the conversion. The output point features do not have the same fields as the input table.

If you want the output points to have  all of the attributes of the input table (in addition to the new notation field) you must put the tool in a Model Builder model that uses the Join Field tool to attach the original fields.

 

 

The model would look something like this:

CCN with Join

 

 

 

 

 

 

 

 

This table lists the coordinate notations mentioned above, and shows the different tools and functions that support them.

System and Tool matrix

 

 

 

 

 

 

 

Content provided by Matt Funk

 

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ArcInfo Workstation to ArcGIS Desktop Command Glossaries

Have you ever wondered what is the equivalent ArcGIS desktop command for an ArcInfo workstation command?  Have you ever wondered what the equivalent python command is for an AML function or Directive?

The Geoprocessing team has created the following glossaries to allow workstation users find corresponding ArcGIS Desktop commands.  In many cases the mapping of functionality and commands between Workstation and ArCGIS Desktop is straight forward and obvious.  Sometimes, however, finding the corresponding Geoprocessing tool in Desktop is not straight forward and obvious, and these glossaries are a helpful resource for those of you that are using workstation in conjunction with Desktop.

Workstation to Desktop Glossaries:

In addition to these glossaries, in 9.4, you will be able to use the new search functionality with Arcmap to search for Workstation commands and the corresponding Geoprocessing tool will be returned if there is a match.  These glossaries will be used as a source for populating the keywords to ensure the search mechanism is as accurate as possible. 

Keep in mind; we recognize that these glossaries do not show every alternative for workstation functionality within Desktop.  As a result, we will continue to update these documents and if you have suggestions or alternatives, please let us know.

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