iPad Geotagged Images for Use in ArcGIS
Information on using images captured with GPS enabled iPad. Have not tested this with WiFi only iPad
using 3rd party GPS such as Bad Elf. This involves no additional Apps for the iPad other than the default
Apps.
Images captured with a GPS enabled iPad are geotagged with the latitude and longitude of the position
of the iPad when the image was taken. Using Photoshop (File > File Info) the image data can be
examined. With version CS 6 there is a GPS tab in the File Info window. With previous versions of
Photoshop, viewing the Raw Data in the File Info window, confirms the GPS data. The Raw Data window
shows quite a bit of information about the image and the settings used by the iPad to capture it.
iPad photos and ArcGIS
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Images can be transferred from the iPad a number of different ways. If there are not too many photos
they can be emailed from the Photos app. E-mailing is limited to a maximum of 5 images per e-mail.
With a large number of images this can be impractical.
Adobe Lightroom recognizes an iPad connected to a computer via the USB cable and images can be
imported directly from the Photo app to Lightroom. When importing, only selected images can be
imported if desired.
Image Capture (Mac) allows transfer of images from the iPad to a computer. Unlike Lightroom all images
from the iPad are copied.
On a PC, when an iPad is connected, the AutoPlay window opens (iTunes opens as well, but you cannot
transfer images from the iPad to the computer using iTunes). From the AutoPlay window there are a
number of options on how to transfer images. Like Image Capture, there is no way to transfer only
selected images.
Once images are transferred, they can be modified in Photoshop or Lightroom. Save or export
(Lightroom) any images as JPEGs for use in ArcGIS and do not remove the XMP files associated with the
images.
For working with the images in ArcGIS it is easiest if the selected images are saved into a unique folder
that is not on the desktop. Keep the folder name short and with no spaces. Use “_” for spaces.
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Following section outlines using geotagged images from an iPad to generate a point feature class in
ArcGIS using the Geotagged Photos to Points tool which was introduced in ArcGIS Version 10.1. This has
also been tested using ArcGIS 10.2.
The ESRI documentation on the tool can be found here:
http://resources.arcgis.com/en/help/main/10.1/index.html#//001700000165000000
Creating a new shapefile from geotagged images
Start ArcMap with a new blank document, or a basemap. This example uses the Clinton 7.5 minute USGS
topographic quad downloaded from the NY State GIS Clearinghouse (http://gis.ny.gov/).
In the Catalog tab, or ArcCatalog, create a File or Personal Geodatabase in a folder on the C drive. This
can be the same folder with the images. Keep the name short.
A geodatabase is needed to create the Point Feature Class with the attached photos using the tool.
Once the geodatabase is created, use the tool Geotagged Photos to Points
(Data Management Tools > Photos > Geotagged Photos to Points) to create a point feature class from
the coordinates associated with each of the images.
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The Input folder is the folder containing the geotagged images.
The output feature class is defined within the geodatabase created above. Be sure to browse to “within”
the geodatabase to name the feature class.
If you want the photos to be viewable on the map, make sure the Add Photos As Attachments box is
checked (this is the default).
Run the tool. When completed the Completed dialog box will appear. Notice the Warning about the
Datum Conflict.
This is because the location data associated
with the images is standard GPS data in GCS
WGS84. The map background, first data into a
dataframe sets the coordinate system, is
NAD27 UTM 18 N.
The points are positioned on the map, but
ArcMap is doing a “projection of the fly”,
transforming from WGS 84 to NAD27 UTM
18N and this warning are to let you know this
is happening.
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The three points (green stars) are the point feature class created from the images as shown in the
Attribute Table associated with the Feature Class.
Using the HTML Pop-Up tool or the Identify tool each point can be queried.
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Clicking on the small image in the HTML Pop-Up tool window opens a full sized image in a new window.
Using the Identify tool brings up a different window. Notice the small paperclip icon and that there is
one attachment. Clicking the down arrow next to the paperclip icon opens a link to the image.
Double clicking the photo link opens the photo in a new
window. Clicking “open attachment manager” opens a
window that allows you to open, or save the image.
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Accuracy
The iPad GPS chip is on par with most consumer/recreational grade GPS units with an accuracy of 10-30
meters on average. The iPad uses a combination of cellular tower triangulation along with GPS to
attempt to provide better accuracy. The cellular and GPS antennas are mounted at the top of the iPad
near where the “Face Time” camera is located. The case in this area is plastic rather than metal to keep
from blocking the cellular and GPS signals. The GPS signal is a fairly weak radio signal and covering the
GPS antenna area with your hand can significantly degrade the quality of the signal being received by
the GPS antenna. Be careful how you hold the iPad while taking photos.
Opening the attribute table for the feature class, no X, Y, or Z coordinates are displayed. Using the Add
XY Coordinates tool,( Data Management Tools > Features > Add XY Coordinates) the X, Y, and Z data
from the iPad can be added to the attribute table.
Notice that the coordinates range from 3
to 6 places to the right of the decimal
point. In Decimal Degrees, accuracy is a
factor to how many places there are
significant digits to the right of the
decimal point. Table shows how
accuracy varies. Note that latitude
governs this as well. With 3 decimal
places accuracy at 45 degrees latitude is
approx. 78 meters and with 6 decimal
places, accuracy at 45 degrees latitude is
approx. 78 mm or 0.078 meters. In
Photoshop the coordinates were defined in Degrees, Minutes & Seconds. At the Equator, a second of arc
is 1/60th of a nautical mile or 30.87 meters (101.3 feet). This distance changes with latitude and can be
calculated by 30.87 * cos (degree latitude). At 43 degrees latitude (Clinton) the value is 30.87 * cos(43)
or 30.87 * 0.73135 = 22.576 meters. The location data is in whole seconds of arc, so the finest distance it
can define is close to 23 meters (74 feet) of accuracy at this latitude.
This is a case of where you should consider precision vs accuracy. Just because a calculation can be
carried to 6 decimal places does not necessarily mean that the measurement is that accurate. The iPad
is not a replacement for a $6000+ Trimble unit with differential correction (at least not yet).
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Another test resulted in a single point for five images that were taken in close proximity to each other
(red star).
Using Add XY tool, the attribute table shows all images with the same coordinates and slight variation in
elevation which is easily within the error of Z with this grade GPS.
In this case the HTML Pop-Up tool is useless as it only allows you to view the top-most image,
photo_1.jpg.
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The Identify tool allows you to see all the attachments associated with this point.
Clicking on an individual image in the list will change the file that is displayed in the Attachments pulldown as well as the image listed in the path. Double clicking in the Attachments pull-down will open the
selected image. You can also click the hyperlink (yellow lightning bolt) next to the Path to open the
selected image directly.
Using the iPad’s capability to capture geotagged images and
ArcGIS’s new capacity to create a georeferenced feature class
from the images and seamlessly attach the images to their
respective points makes for a great data gathering tool.
An app like GIS Pro adds a great deal more functionality to
collecting data and images with the iPad, but at a steep cost
($300) and a difficult learning curve. This system allows anyone
to immediately collect and georeference data. Once the dataset
is constructed, adding additional fields to the feature class
attribute table allows notes and other information collected in
the field to be added to the point attributes as well.
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