Collect Features task

Working in the field, you think about the individual objects or types of objects that you need to collect, search for, and update. These objects are called features in the ArcGIS Mobile application. They are organized by their type and can be grouped based on a mapping classification called a layer.

Using the Collect Features task, you can choose from a dictionary of feature types that were prepared for you and collect a new instance of one by either using the stylus or rocker on your device, using a GPS receiver, or entering coordinates directly if you have a separate handheld GPS or laser rangefinder device.

The Collect Features task provides you with a dictionary of feature types to choose from when you need to collect a new object or feature in the field. Your GIS staff has defined the set of feature types that you are using and assigned each type with some rules regarding the way that you collect both the shape of the feature and the attributes. All these settings are defined within the project that you are working with.

The task will guide you through the collection process using these three primary steps.

Choosing a feature type to collect

To collect a new GIS feature, first tap the Collect Features task. Note that when your GIS staff created this project for you, they may have renamed the project to something else like Create Incident Report or Locate Infrastructure. However it was named and described, you can identify the Collect Features task by its graphic icon.

The first step in the collection task is to specify the type of feature you want to collect. The list of presented feature types on the Choose Feature Types page is organized in alphabetical order. However, as mentioned above, each feature type has been organized or grouped by your GIS staff into a layer, and you can, therefore, group the list of feature types based on the layer they are contained within if that organization makes more sense to you.

Each type is defined by both the symbol that is used to draw features of that type on the map and a name.

Sometimes the list of feature types that can be collected in the field gets quite long based on what type of fieldwork you perform and how your GIS staff organized the project. For example, if you are managing a tree species inventory, the list of feature types can include every type of tree species you encounter in the field. To quickly find the feature type you need to collect, there are several ways to organize and filter the list of types that appears on the Collect Features page.

To quickly find the feature type you need to create, you can do the following:

Search for feature types

Using the handheld version of the field application, lists get long quickly. For this version of the application, You can search through the list of feature types to find the one you are interested in by typing in a search box. As you start to type, the list of feature types will be reduced to display only the types that contain the letters that you typed in. You can clear the search list by tapping the Clear button.

Group feature types by layer

By default, the feature types are displayed in alphabetical order; however, you can group the list of feature types based on their layer name.

This will help to organize the list based on how the feature types are managed using layers in the map that has been created for your project. You will need to choose a feature type to continue the collection process.

Filter the list of feature types

Searching for a feature type will reduce the list based on the letters that you type, but you can also choose for which layers you want to display feature types. If you have to collect a lot of different feature types, this reduces the list to a more manageable size.

To filter the list based on layers, tap Choose Layers and pick the layers for which you want to display feature types.

If the list of feature types is still difficult to manage, or if the feature type you are looking for is not in the list, it is recommended that you contact your administrator and either have the project updated or a new one created that is more manageable.

Collecting the feature's shape

Once you have chosen the feature type you want to collect, you can either collect the geometry of the feature or the attributes for the feature. You will see a check mark next to Geometry and/or Attributes when the collection for each is satisfied. Note that you may not need to collect any attributes to finish the task.

When collecting the shape, there are several collection methods you can choose from:

What you need to know about collecting data using a GPS receiver

When you are using a GPS receiver to collect the shape of a feature, you need to be aware of the quality of the GPS positions that you are receiving. Depending on your field conditions, the time of day, and a host of other variables, you might encounter problems using your GPS receiver that you could not predict before going to the field. In these circumstances, it is important that you are able to understand how ArcGIS Mobile works with a GPS receiver and how you can alter the GPS collection settings so that you can accomplish your work.

GPS data collection in ArcGIS Mobile uses the concept of a quality filter to help you in getting the best accuracy from your receiver. The GPS quality filter is set for each feature type you can collect in your project and is based on two key factors: GPS fix type and Position Dilution of Precision (PDOP). When you choose a feature type and GPS collection method, you will see a visual indicator determining if the quality filter settings are met with your current GPS fix or if they are not. If the quality is good, you will see a green indicator. If the quality is bad, you will see a red indicator and will not be able to collect data using this method. When red, you may be able to alter the quality settings however it is recommended that you have a good understanding of GPS concepts and data capture best practices before doing so.

GPS fix type

Depending on the GPS receiver in use and the type of GPS data collection you are performing, you might want to filter the positions received from the GPS receiver based on a certain fix type. For example, you might want to ensure that only differentially corrected GPS locations are used in the averaging process, ignoring all autonomous read positions when using a WAAS-enabled receiver.

If the GPS fix type from your receiver is different from the GPS fix type that you established when setting the quality filter, you might still be able to average GPS positions. This can occur if the fix type you are receiving is of higher quality than what the filter will accept. The hierarchy of fix types is as follows:

  • GPS fix
  • Differential GPS fix
  • Real-time kinematic
  • Float real-time kinematic
  • Estimated fix

For example, if the GPS receiver fix type is differential GPS (DGPS) fix and the filter setting is GPS fix, you will be able to average positions.

PDOP

In addition to the type of fix that you are receiving, you might also want to filter positions based on the geometric strength of the GPS satellite configuration. PDOP is a numeric value representing the amount of error in the position read. Setting a PDOP value as part of the GPS quality filter will ensure that only positions with a PDOP equal to or less than the set value will be used to create the average.

You can always see what the current quality filter settings are by tapping Quality Filter from the GPS Collection Settings page. If the values cannot be changed, it means that when the project was defined it was determined that the settings specified must be met and cannot be changed in the field. If they are editable, you can change both the required fix type and the PDOP settings within the application.

When ArcGIS Mobile receives positions from the GPS receiver, it will only use positions that meet the quality filter standard that you put in place when calculating a location from averaging or creating vertex locations for lines and polygons when streaming.

For your field workflows, you will know if your GPS is receiving positions that meet the quality filter before you start data collection. A green circle will indicate that the quality filter standards have been met or a red circle will indicate that the quality filter standards have not been met.

If quality filter standards are not met, you should first look at the GPS status to identify what the GPS fix type is and what the PDOP value is. From there you can access the GPS collection settings and start troubleshooting. If your GIS staff has allowed you to change the GPS quality filter settings, you can alter the maximum PDOP value and change the fix type. An example of what you could encounter is that your quality filter has established that DGPS is the fix type required for collection but you cannot acquire a DGPS signal from your receiver given your current time of day or field location.

GPS collection settings are established for each feature type that is set up for collection.

GPS averaging collection method

You can use a technique called GPS averaging to collect vertex locations using a GPS receiver. This technique provides the most accuracy possible when collecting point, line, and polygon shapes. It involves the act of physically standing at or near the location for which you need to capture a point or vertex, receiving a set interval of GPS positions from the receiver that meet specified quality standards for the feature type, then averaging the results of all positions collected.

When you choose the Collect Using GPS Averaging method, you are presented with a very simple experience of starting and stopping the averaging process. If you haven't yet connected to your GPS receiver inside the application, you can quickly do so from the settings page. After acquiring a GPS signal that meets the quality standards set for the feature type, you can start the averaging process. Doing so, you see a counter that updates as positions are read from the GPS receiver for use in calculating an average.

Once you have captured the required number of positions, the averaging process stops. If it does not stop, your GIS staff has determined that you should continue to collect positions until you manually stop the averaging process. If you are having trouble receiving enough GPS positions, check to see if the quality settings are being met. If the quality settings are good, there is a green indicator on the page. If they are bad, there is a red indicator on the page.

The recommended number of positions that were set for GPS averaging, along with the application behavior of stopping the averaging process, is initially set when the project is created in the office. However, you have the ability to change these settings by clicking Averaging Settings.

If you are collecting a line or area feature, starting the averaging process creates the next vertex in the feature. If you are unhappy with the shape of the vertex you just collected, click Remove Last Location.

The number of positions that need to be received to compute an average is a property of the GPS collection settings. Depending on field conditions, you might need more or less than the value specified. The value is therefore a recommended minimum. At any time you can stop the collection process. If you stop the averaging process before collecting the minimum value, you are notified that you have captured fewer than the minimum number of positions required, but you still have the option to accept.

During the collection process, you might also encounter problems acquiring a GPS signal. If this happens when collecting positions using GPS, the GPS display icon begins to flash. GPS positions received during this time will most likely not match your GPS quality filter settings. If problems persist, you should either lower the filter constraints or consider using an alternative method for collecting the location. For example, if you cannot acquire a good GPS signal because you are too close to a building, pace off from where you are standing to a location where you can receive a good fix and use the Offset Location tool to locate the averaged GPS location to the desired location.

GPS streaming collection method

The GPS streaming collection method can be used for the creation of line or area features and is useful for GPS-based data collection while in motion (walking, driving). GPS positions that meet the quality filter standard set by your GIS staff when authoring your mobile project are used to create vertices of line and area features at a set time or distance interval.

GPS receivers acquire a GPS position roughly once per second, so it is important that you filter the number of positions that are used to construct your line or area features. If you do not, the shape will be too complex and difficult to manage once synchronized to the server.

GPS streaming settings are used to define the method for filtering the number of positions from the receiver. You can filter based on either a distance or time measurement. As with GPS averaging, the streaming settings are per feature type, so you have a great deal of control based on what you are collecting. With that said, however, the shape and size of the feature you need to collect influences the interval as well. For example, if you need to collect a track or trail that you are walking, you might want to choose a time interval that best suits the speed you are walking.

Using the map

You can collect the shape of the new feature using an input device or tapping on the map to set the location. The current location of the cursor indicates the location of the vertex that will be collected if you tap on the map.

From the map page, you can remove or undo the last location that you entered on the map or offset the location entered. Note that within the application settings you can enable snapping. By default snapping is turned off.

Using x,y coordinates

If you are collecting vertices, you can directly enter an x,y location for a point. This can be quite useful if you are using a GPS receiver that is not connected to or compatible with your mobile device. Most of these receivers have their own display and can represent location in decimal degrees. Note that the Using XY Location method is looking for coordinates stored in WGS84 format. You should check your GPS receiver to make sure it is displaying coordinates using WGS84.

Coordinate types include decimal degrees using the WGS84 transformation. You should always use WGS84 if you are receiving longitude and latitude readings from an external GPS unit.

By default, the longitude and latitude values that are displayed on the dialog box represent the location at the center of the map display.

Geometry options

Once you define the shape of the feature you are collecting, there are options that can be performed on the geometry itself; for example, you can offset the geometry or remove the last location collected.

Setting field values

Each feature type in the Collect Features list has a set of default values that are applied to a newly constructed feature based on how your GIS staff defined the map. After setting the location of the feature, the Edit Attributes page displays a list of fields and a set of entry boxes into which you can enter values.

Depending on the type of information you need to enter, you could see a different entry dialog box. Where possible, a list of values appears so you do not need to type. This will help you avoid typing mistakes. Also, certain field values may require that you input a value. Required values were established by your administrator.

Once you are finished setting field values, you are presented with a number of options. You can choose to collect another feature of the same type and retain the values that you have just set for the feature you constructed, choose another feature type, view the results of your collection on the map, or simply finish your collection.

Finishing page

Once you have collected a new feature, you can choose what to do next:


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6/15/2011