Collecting Data

Collecting data refers to adding features and attributes. It is normally done either by reference points on the map or by using GPS and is one of the primary functions of the app. Because this is an inherently mobile task it is very well suited to iOS devices due to their mobility, GPS, cameras, and touchscreen displays.

From a workflow perspective, you would want to have your feature classes prepared before collecting the field data. You would also want to download offline maps and any raster imagery beforehand in the case where you might not have a data connection at the collection site. Workflow is discussed at greater length here.

To add a feature, press the "+" button at the top left of the map. The first time you do this you will be presented with list of feature class datasets. Those that are not enabled for your current project will not be displayed. The next time you visit this dialog it will remember your selection and automatically select the dataset you chose the last time. However, if you need to change the dataset you are choosing from you can still back up any time using the back button in the top left of the dialog.

There is also a special set at the top of the list that only includes feature classes used in the current project. This is another method to save some time if you will be using the same ones repeatedly.

Adding Points

To add a point, simply select the point-based feature class you would like and then position the map so the crosshairs indicate where you would like to place it. You can use any of the typical pinch or swipe gestures to navigate the map to where you need it to be. We found that using the center of the map is more accurate than placing with your finger. It also can be very convenient when combined with any of the other features that position the map such as search or the "Center on Me" button. For example, double-tapping on the spot where you would like to place your point will zoom and also center the map at that location. If you were exactly where you wanted to place the point then you are all set. Press the "Place" button in the lower right corner when you are ready to create the feature.

After you have added the point it will automatically select, which will bring up its attributes in the menu. Since the menu is not visible on the iPhone, an "Attributes" button appears in the bottom toolbar for convenience. Editing the attributes will be discussed later.

Adding Lines and Polygons

Adding lines and polygons is very similar to adding points--you start with the add feature dialog, and after you have selected a feature class will be in the line creation mode on the map.

You will notice a few new times, such as the distance display at the top. This shows the distance of all the points that have been placed so far. Adding new points is again fairly straightforward. Center the map on your next point and press the "Add Point" button that is floating over the map. If you would like to remove the last point placed simply press the floating "Undo" button. If you feel like you need more room on the iPhone, you can rotate it to a landscape mode and continue adding points without the toolbar. Polygons will automatically close (creating the last segment) when you press done.

Finally, you can also add points using the GPS. You could do this one at a time manually by pressing the "Center on Me" button. Alternatively, you can press the "Record With GPS" button to schedule the phone to record periodic points from the GPS. The leftmost portion of the button will present the GPS settings panel and allows you to control how the recording of points gets filtered. We tried to include enough self-explanation in this panel to make sense on the fly so a full discussion is not made here. However, it is helpful to know a few things about the iPhone's GPS and the general manner that this works so a more detailed explanation of this is found below.

Searching

You can search your project for different kinds of data. You may search for a specific coordinate or you can search for a feature by title, attribute or value.

Coordinate Searching

The following formats for coordinate searching are currently supported:

• UTM
• Latitude/Longitude
• 0.00000°
• 0°00.000'
• 0°00'00.00"

The following are valid examples of usage in these formats (notice punctuation or the lack thereof):

• 12T 412345 4123456
• 34.56789, -111.23456
• 34.56789 -111.23456
• 34 56.789', -111 23.456'
• 34 56.789, -111 23.456
• 34 56' 12.34", -111 23' 45.67"
• 34 56 12.34, -111 23 45.67

Because of the map servers used, the native datum for GIS Kit/Pro is WGS84. As of version 1.9, you are able to specify the coordinates in a search from a different datum from the default WGS84. The following datums are supported for searching:

• NAD83 (North American Datum 1983)
• NAD27 (North American Datum 1927)
• OSGB36 (also just OSGB - Ordnance Survey GB 1936)
• ED50 (European Datum 1950)
• SAD69 (South American Datum 1969)

To specify one of these datums for searching, simply add the abbreviation, followed by a space before the rest of your coordinates. For example: "NAD83 12T 412345 4123456".

GPS in the iPhone and iPad

Various models of iOS devices have real GPS hardware and can provide accurate locations nearly anywhere on the planet, regardless of cellular service or wifi connection. We get many questions about this so we will attempt to be very clear. Here are the devices we know to have actual GPS hardware:

• iPhone 3G
• iPhone 3GS
• iPhone 4
• iPhone 4S
• iPhone 5
• iPad 3G

GPS Accuracy

We are often asked about the accuracy of the GPS on the iPhone and iPad. Unfortunately, we have not yet carried out a proper scientific experiment to be able to give any conclusions. However, from our experience we can say that it is typically within ten feet or better under normal circumstances. Of course, this can be heavily influenced by many conditions such as canopy, view of sky, interference, etc. so we are refraining from making any blanket statements until we get enough time to do a proper study. The iPhone 4S has included support for the Russian GLONASS constellation and it appears from early trials that lock times, accuracy, and robustness have all improved as a result.

Bluetooth GPS Receivers

We have heard from customers that good results are possible with third party GPS receivers. We have personally tested the Bad Elf receiver with a wifi first-gen iPad and it worked really well on this project in Haiti. Any receiver that works with the iPhone/iPad/iPod should work fine with our apps.

GPS in GIS Kit/Pro

The way the iOS interface to location services is fairly simple, which is nice in many cases but limiting on others. We are provided with periodic points as they come in from Apple's hardware. We do not have access to the satellite information nor the raw data coming from the satellites. In our experience the points come in as fast as three per second when the signal is strong. In many cases, this is more data than you want to record, so we provide filters to limit the number of these data points that are retained.

We provide to you three types of filters: distance, time, and accuracy. When set, the distance filter will ignore points that lie within a given distance from the previous point. This can be helpful to limit points when lengthy stops might cause accumulation of useless points. The time filter just ignores incoming points until the given duration since the previous point. Finally, the accuracy filter will cause inaccurate points (as determined by the iOS hardware) to be ignored.

The Ultra Accuracy setting is available but generally unnecessary and not recommended due to its high power consumption. According to Apple:

"Use the highest possible accuracy and combine it with additional sensor data. This level of accuracy is intended for use in navigation applications that require precise position information at all times and are intended to be used only while the device is plugged in."

So, we provided it as an option for you to use at your own discretion.

GPS Track Logging