I'm running into a Houdahgeo accuracy bug when importing images (JPEG, TIFF, NEF, etc.) that already have GPS data written by the camera.  Houdahgeo is rounding coordinates too severely, resulting in locations appearing on the other side of the street.  For example, if I have a photo with a longitude of -121.865260° in the EXIF file, Houdahgeo will turn it into longitude -121.865000° when displaying or writing GPS EXIF data.  The next longitude that Houdahgeo understands is -121.865278°, which came from a photo taken at the actual location (in the EXIF) of -121.865296°.  No matter what the coordinate is in the EXIF file, Houdahgeo will round it by the equivalent of a number of meters on the ground.  Latitude is rounded in a similar way.

How do I get Houdahgeo to use higher precision and not mess up the coordinates?

Here are the technical details:  The hexadecimal GPSLongitude field in the EXIF file is:
00000079 00000001 00000033 00000001 00081b8d 000025c8
This represents 121/1° + 51/1' + 531341/9672", which is 121° 51' 54.936", or 121.865260°.
Houdahgeo takes this value and appears to incorrectly truncate it to the nearest second, resulting in
121° 51' 54", or 121.865000°.  The next longitude that Houdahgeo understands is 121° 51' 55", which is 121.865278°.

Context: I'm trying out Houdahgeo for geotagging as well as viewing files.  I have a camera-based logger which writes coordinates directly into the photos.  I can create my own tracks by extracting coordinates from series of photos into GPX files using a script, but that's not relevant here since the problem occurs even without any tracks.

0 0
This might actually be Photoshop's fault.  I see that it's writing an extra XMP section with the GPS coordinates truncated to seconds into files it saves, and Houdahgeo may be picking up the wrong Photoshop-munged coordinates instead of the EXIF ones.  I'll investigate further.
0 0

I am surprised to hear HoudahGeo should truncate values.

Could you email me a sample image so I can investigate this?

Pierre Bernard
Houdah Software s.à r.l.

Houdah Software s. à r. l.

HoudahGeo: One-stop photo geocoding
HoudahSpot: Advanced file search utility
Tembo: Easy and effective file search
0 0
Yeah, it's Photoshop that's corrupting the coordinates.  If I delete the XMP metadata it's inserting into files it saves, the correct coordinates reappear in Houdahgeo.  Sorry for the trouble.
0 0
It turns out that Houdahgeo does truncate coordinates of already geocoded images, although not as badly as Photoshop.  I did the following test:

- Create a JPG image that was geocoded to 39.71985333° N, -121.86529667° W.  I made sure that these coordinates were in both the EXIF and XMP metadata of the JPG.

- Open the JPG image in Houdahgeo, without using any tracks or geocoding it in any way. Houdahgeo displays the coordinates in its window as 39.719853 and 121.865297.  That's less accurate than the original, but still good to a decimeter.  I'm hoping that it's only the display that is rounded, not the actual data.

- Save the JPG image's EXIF/XMP metadata from within Houdahgeo without having changed the image at all.

- Look at the EXIF and XMP images in the updated image.  They were more severely rounded to 39.71985000°, -121.86530000°.  We lost three decimal places here.

- Open the saved JPG image back in Houdahgeo. Now Houdahgeo displays its coordinates as 39.719850 and 121.865300.  That confirms that Houdahgeo rounds the coordinates severely enough that it's not even able to round-trip them.  The error is now about a meter.

There are two attachments here:  "First.jpg" is the input image to Houdahgeo. "Second.jpg" is what Houdahgeo saved it as, without me doing any geocoding within Houdahgeo.
Click image for larger version - Name: First.jpg, Views: 5, Size: 42.46 KB Click image for larger version - Name: Second.jpg, Views: 5, Size: 43.30 KB
0 0