Posts Tagged ‘geotagging’

Photo file format face-off: JPEG versus PNG

May 19, 2011

iPhone cameras save photos as JPEGs (JPGs), a “lossy” compression format; shooting uncompressed RAW images is not an option. If you edit a JPEG photo, then the resulting image file will be further compressed when you export the file from your photo editor of choice. Question is, if you edit a JPEG image (using say, Aperture 3 by Apple Inc.) then how can you export the image without further compression?

One solution to this problem is to use a “lossless” compression format such as PNG. But there’s a problem with PNGs: PNG doesn’t support EXIF/IPTC; if you export a JPEG file as a PNG, then the EXIF/IPTC info is lost (e.g., geolocation info). That’s an unacceptably BIG trade-off for me, especially since I’m not sure the difference in image quality between JPEGs and PNGs is noticeable. So I set up a face-to-face comparison test.

There are four pairs of photos in the following gallery: A cropped version of a JPEG photo, exported as a JPEG file; followed by the same cropped JPEG photo exported as a PNG file. You tell me — are the PNG versions noticeably better than the JPEG versions? Comments are invited and welcome.


Field test: Leafsnap app

May 16, 2011


Leafsnap app (free) is “an electronic field guide for tree and plant species.” See the video, “Introducing Leafsnap” for more information. Leafsnap is available in the Apple iTunes App Store.

I field tested Leafsnap recently. I selected several trees located on the grounds of Mount Vernon Unitarian Church in Fairfax County, Virginia USA. One the trees in the test group is an old Black Locust tree. The gallery (shown above) features a photograph of a Black Locust tree leaf taken using Leafsnap’s “Snap It!” feature (No. 1), a series of screen captures from Leafsnap (No. 2 – 4), and a couple of photos of the tree taken using iPhone’s built-in Camera app (No. 5 – 6). The screen captures illustrate the process used by Leafsnap to identify the Black Locust tree based upon the outline of one of its leaves. Notice the Five-lined Skink lizard in photo No. 6.

When Leafsnap’s “Snap It!” feature is able to connect to remote servers via either 3G or Wi-Fi, the automatic identification process works very well; when Leafsnap is unable to establish a connection, you’re dead in the water and going nowhere. Hopefully the problem establishing a server connection has been resolved in the latest version of Leafsnap. Overall, Leafsnap is a “must-have” app for educators, gardeners, and natural science enthusiasts.

Tech Tips: For trees with compound leaves (such as Black Locust), be careful to shoot the entire leaf. Leaves should be photographed in situ for accurate geolocation. Photos saved to the Camera Roll from Leafsnap’s built-in camera (“Snap It!”) are not geotagged. For this reason, you may want to take one or more photos using iPhone’s Camera app. (See the location of the Black Walnut tree, derived from the EXIF/IPTC info for photo No. 5.)

Mount Vernon Farmers Market Panorama Photos

May 11, 2011

Mount Vernon Farmer’s Market — located in the parking lot of Fairfax County Sherwood Regional Public Library — is open Wednesdays from 8:00 a.m. to 12:00 noon, May through November.

I used 360 Panorama app ($1.99) to shoot several geotagged panorama photos of the farmers market. Hyperlinks to online interactive versions of the panorama photos are listed following each “flattened” version, shown below. Very dynamic venues are not ideal locations for panorama photo shoots, as you can see by the blurry images of people moving around the farmers market.


Panorama Photo 1 (interactive version)


Panorama Photo 2 (interactive version)


Panorama Photo 3 (interactive version)


Northern Virginia Photographic Society field trip to Huntley Meadows Park

May 7, 2011

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Field test: Photosynth app

May 6, 2011


I used Photosynth app (free) to shoot the preceding geotagged panorama photo of Milway Meadows, a residential community in Fairfax County, Virginia. An online interactive version of the photo simulates virtual reality, enabling you to see what I saw (Silverlight required, the Microsoft equivalent of Adobe Flash). That is, assuming you aren’t using the Safari Mobile Web browser on an Apple iOS mobile device. Seriously, why would Microsoft choose to use a platform like Silverlight that excludes a significant percentage of the market for mobile devices from using their product? That’s a business model that makes NO sense!

There is a free app called iSynth that is billed as a Photosynth viewer. I downloaded, installed, and tested iSynth on my Apple iPhone 3GS and iPad 1. A simple search caused iSynth to crash on BOTH devices, and now it crashes every time I try to launch the app. Based upon my experience, I think it’s fair to say iSynth is not ready for prime time.

Photosynth is an interesting solution to the problem of how to stitch together a series of overlapping photos to create a panorama photo. As you turn around an axis of rotation, Photosynth displays a green frame that indicates the camera is correctly positioned to take the next frame; then Photosynth shoots the photo automatically. Sounds simple, right? If only the process worked better! You don’t have to look very closely at the panorama photo (shown above) to see the seams between frames; in some places, the frames are obviously misaligned. Contrast the Photosynth app panorama photo with the same scene shot using AutoStitch Panorama app, and I think you’ll agree with me that AutoStitch is still King of the Hill in the field of photo-stitching panorama apps.

Better Geotagging, revisited

May 2, 2011


In a recent blog post, I shared a simple tech tip for better geotags in iPhone photographs: Launch the Maps app and verify your location BEFORE taking pictures with the Camera app. I should follow my advice! Huh? Look at the Flickr Map (shown above) of my photo gallery, “April showers bring May flowers.” All of the photos in the gallery should be located on three streets in Hollin Hills (listed in chronological order along my photowalk): Elba Road; Nordok Place; and Mason Hill Drive. As you can see by looking at the map, there are several outliers that are not located (geotagged) correctly. Question is, what caused the photos to be geotagged incorrectly?

Apple iPhone is the best all-in-one device for geotagging photographs, as I explained in “The ABCs of A-GPS.” iPhone “Location Services,” as good as it is, can be surprisingly inaccurate after an iPhone has been either in sleep mode or powered-off. It was raining lightly during most of my photowalk through Hollin Hills on Sunday: When I stopped to take photos, I was in a rush to prevent water damage to my iPhone and did not use the Maps app to verify my location before shooting pictures; my iPhone was in sleep mode between stops along the photowalk. Net results: My iPhone wasn’t damaged (that’s good news); several photos were geotagged incorrectly (that’s bad news). Perhaps I could have avoided the problem by running a GPS-tracking app in the background, such as MotionX GPS. Point is, you can’t assume an iPhone will correctly geolocate every photograph you take with its built-in camera, but you can get better results by using the Maps app to get an accurate position fix before taking photos.

Finally, a quick word about the Flickr photo sharing service. Is it just me, or is the Flickr user interface often less than intuitive? I was sure I set up my Flickr account to enable sharing photo location information. Turns out I was wrong. I discovered the solution after troubleshooting the problem. Sign in to Flickr. Click on the hyperlink labeled, “Your account.” See the section entitled, “Defaults for new uploads”; for the setting, “Import EXIF location data,” select “Yes.”

iPhone Photography Tech Tips: Better Geotagging

April 18, 2011

Here’s a simple tech tip for better geotags in your iPhone photographs: Launch the Maps app and verify your location BEFORE taking pictures with the Camera app. You’d be surprised how inaccurate “Location Services” can be after an iPhone has been either in sleep mode or powered-off.

Field test: 360 Panorama app

April 4, 2011


I used 360 Panorama app to shoot the preceding geotagged panorama photo of Milway Meadows, a residential community in Fairfax County, Virginia. The same panorama photo was uploaded via Posterous app (shown below); most of the EXIF/IPTC info, including GPS Info, is missing due to a bug in Posterous app for iOS. An online interactive version of the photo simulates virtual reality, enabling you to see what I saw! Can you see where the panorama came full circle? Let’s hope the developers at Occipital are able to figure out a clever solution for this glaring problem.


Contrast the 360 Panorama app photo with the same scene shot using AutoStitch Panorama app.

Equinox sunrise

March 21, 2011


I visited Huntley Meadows Park to photograph sunrise on the March Equinox, 20 March 2011. I used Theodolite Pro app to record a time series of geotagged screen captures beginning at 7:12 a.m., the official time of sunrise in Washington, D.C. on March 20th. On the equinoxes, the Sun rises due east (90 degrees azimuth) and sets due west (270 degrees azimuth). Looking at photo 1 of 6, notice that the camera is facing due east (090°) and the disk of the Sun is below the tree line at 7:12 a.m.; by the time the Sun is clearly visible at 7:28 a.m. (photo 5 of 6), the Sun had moved along its path across the sky to a point slightly south of east (see Editor’s Note, below).


I used Pro HDR app to shoot a composite image (shown above) of the scene looking eastward across the wetland. Notice there is some ghosting visible along the tree line, probably due to the fact that I was too cold to stay still for a handheld shot!

Related Resources:

Editor’s Note: Sunrise is defined as the time of day when the Sun’s upper limb appears above the true horizon. From my viewpoint at Huntley Meadows Park, the true horizon was obscured by the visible horizon (the tree line). Therefore, I was unable to see the Sun‘s disk on March 20th at exactly 7:12 a.m.

Planet Earth is a magnificent timepiece! The Earth rotates counterclockwise once every 24 hours. One complete rotation equals 360 degrees. The rate of the Earth’s rotation equals 15 degrees per hour:

360°/24 hr = 15°/hr or 15°/60 min, which reduces to 1°/4 min

Notice that the first five photos were taken approximately four (4) minutes apart; photo 6 of 6 was taken two (2) minutes after photo 5 of 6. Therefore, 18 minutes elapsed between the first and last photos. That means the Earth rotated 4.5 degrees during the photo shoot. Do the math:

18 min/1 x 1°/4 min = 4.5°

Now we know the Sun’s azimuth was 94.5 degrees when photo 6 of 6 was taken. No wonder it appears as though the Sun didn’t rise due east on the Equinox!

Combined GPS Track & Photo Gallery for Display in Google Earth

March 11, 2011


As promised in my last post, Photowalking Hollin Hills, here are step-by-step instructions describing the workflow for creating a KMZ file that features a GPS track and gallery of geotagged photos, suitable for display in Google Earth.

  1. Save- and export a track (GPX file) from a GPS device, such as MotionX GPS for Apple iPhone.
  2. Create a gallery of geotagged photos using Picasa for Windows.
  3. From the menu bar in Picasa, select Tools/Geotag/Export to Google Earth File; save the resulting KMZ file to a known location. (Editor’s Note: This option is not available in Picasa for Mac OS X.)
  4. Open the KMZ file of geotagged photos in Google Earth.
  5. Open the GPX file (GPS track) in Google Earth; drag the GPX file into the KMZ folder of geotagged photos.
  6. Select the KMZ folder (containing both the GPX track and geotagged photos). From the menu bar in Google Earth, select Save/Save Place As…; create a name for the new KMZ file and save to a known location.

A sample KMZ file (Picasa_23Feb2011.kmz) is shown above.

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