Bar Harbor 2008 Color IR

                                Horizontal_Positional_Accuracy_Report: Consistent with national standards for 1' ground sample distance (GSD).
                              

                                Imagery for the Town of Bar Harbor was acquired on April 19, 2008 using a Z/I Digital Mapping Camera (DMC). This metric digital camera is capable of capturing true color, color infrared (CIR), and panchromatic (B&W) imagery at the same time.  Positioning of the image centers were also captured using Airborne GPS (AGPS).  Imagery was captured for an output suitable for a 1' ground sample distance (GSD).  Richard Crouse & Associates of Frederick Maryland were selected to provide this service. 

The coordinate system is Maine State Plane Coordinate System, East Zone, and the horizontal datum is NAD83.  Units are in US Survey Feet.  The vertical datum is NAVD 88.

Previous control points (from the 2004 aerial mapping project) were refreshed with new paint so that they would be visible for the 2008 imagery.  The ground control was tied to the AGPS data.  Pass, tie, and ground control points were measured using SoftPlotter 4.1.  Albany software was used to aerotriangulate the data.  Maximum residuals were less than 0.5 feet for X, Y, and Z.  

Digital Terrain Models (DTM) are a necessary component to create ortho-rectified imagery.  In this case, the existing 5' contour interval DTM was used, which was photogrammetrically captured from the 2004 imagery. 

Digital orthophotographs (1.0' ground sample distance) were created from the aerial images, the camera calibration report, the aerotriangulation data, and the existing 2004 DTM.  A cubic convolution algorithm was used to orthorectify each image (using SoftPlotter v4.1 software).  Mosaicking was performed with INPHO  OrthoVista 4.2 software.  Mosaicking occurred along sharp linear features when possible and linear feathering was used to the blend the images.  

Previous stereo-compiled planimetric features were compared to the same orthophoto features to ensure proper alignment.  Image color was enhanced slightly with Adobe PhotoShop' s image adjustment tools.  This step improves visual appeal without affecting positional accuracy.  After the composite image was finalized, it was tiled with OrthoVista software. Typical tiles sizes for TIFF (with appropriate world file TFW) images were in the 150 MB range.  Lastly, TIFF images were compressed (20:1) to MrSID image format using LizardTech's compression software.  Both true color and CIR ortho tiles were delivered to the Town of Bar Harbor.

The aerotriangulation results and the raw color-infrared images were also provided to Fred Dibello of Stantec for vernal pool mapping and analysis.