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1:5,000 Color Ortho Imagery (2005) - April 2005
Download these images
-- Compressed from original 1/2-meter resolution GeoTIFFs:
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These medium resolution true color
images are considered the new "basemap" for the Commonwealth by MassGIS
and the Executive Office
of Environmental Affairs (EOEA). The photography for the entire commonwealth was
captured in April 2005 when deciduous trees were mostly bare and the
ground was generally free of snow.
 Datalayer Description_files/coq2005_5th.jpg) Image type is 4-band (RGBN) natural color (Red, Green, Blue) and Near infrared in 8 bits (values ranging 0-255) per band format. Image horizontal accuracy is +/-3
meters at the 95% confidence level at the nominal scale of 1:5,000.
This digital orthoimagery can serve a variety of purposes, from general planning, to field reference for
spatial analysis, to a tool for development and revision of vector maps. It can also
serve as a reference layer or basemap for myriad applications inside geographic information system (GIS) software.
The project was funded by the Executive Office of Environmental Affairs, the Department of Environmental Protection, the Massachusetts Highway Department, and the Department of Public Health.
Sanborn LLC of Colorado Springs, CO, performed all work for this project. The
source imagery was acquired with a Vexcel Ultracam digital camera at a flying height of 5,070 meters above mean terrain and an approximate pixel resolution of 45 cm.
Forward overlap was approximately 60%, except 80% in areas with tall
structures (downtown Boston, Worcester, and Springfield), in order to
reduce building lean, with sidelap of 33%. The entire state was covered
by about 5500 image frames, captured over seven days from April 9
through April 17, 2005.
The ground control used to support the mapping was collected by
photographic identification of strategic points. The ground control coordinates
were collected via GPS ground survey techniques. Aerial Triangulation was
performed on softcopy workstations using Intergraph ISAT software for photo
measurement and matching. The final bundle adjustment was performed using BINGO
5.2 software.
A new digital elevation model was stereo compiled for the entire State
from the newly acquired 2005 imagery. The DTM includes mass points,
soft breaklines and hard breaklines. The images were ortho-rectified
using METRO, Sanborn's proprietary software. Bridges were modeled in
3-D using standard photogrammetric stereo-compilation techniques on
softcopy workstations. Sanborn's Metro process rectifies the bridges
using the 3-Dimensional model using similar methodologies for
correcting the positional accuracy of other ground features. The
bridges were uniquely coded and later removed from the final
deliverable DTM file.
 Datalayer Description_files/coq2005_2th.jpg) Imagery is georeferenced to Massachusetts State Plane Mainland (Lambert Conformal Conic Projection) NAD83 coordinate system, denominated in meters.
Color balancing was performed using METRO_NICE software. The resulting images were mosaicked into one seamless database of
imagery and extracted to match the existing MassGIS Orthophoto Index Grid tile layout (each image tile covers 4,000 × 4,000 meters on the ground.). Images were quality-controlled by Sanborn using Adobe PhotoShop software. Final deliverables included 1/2-meter pixel resolution GeoTiff images with supplementary tfw files and metadata.
MassGIS quality assurance included rigorous independent checks of the
spatial accuracy using other datasets of significantly higher accuracy,
and field work that included the capture of highly accurate GPS points
that were compared to the same locations appearing on the deliverables.
MassGIS also assessed the visual quality and appearance of the images.
Due to the large size of the original
half-meter GeoTIFF images, MassGIS is also making these images available in the compressed
MrSID and JPEG 2000
(JP2) formats. Options include images tiled by the orthophoto index as
wells as large regional mosaics, which comprise from 26 to 73 ortho
index tiles. Users may access the data by free download from the
MassGIS ftp server or by ordering the data on CD or DVD. Details are
provided below.
Original vs. "Contrast Stretched" Imagery
MassGIS has produced a
set of "Contrast Stretched" MrSID and JP2 data for users who do not
have the software tools to modify the appearance of the original
imagery. This second set of compressed data was produced from a set of
GeoTIFFs that MassGIS modified with a 2.75 standard deviation linear
contrast stretch in Erdas Imagine software. A linear contrast stretch
is a simple way to improve the visible contrast of an image by changing
the individual values of the pixels in the image. Usually, a contrast
stretch is performed only on the display device (screen, printer,
etc.), so that the data file values do not change. In this case, the
stretched pixel values were saved to the tiffs and the tiffs were used
to make the second set of MrSID and JP2 files.
MassGIS is making this second
set of images available for those whose software does not permit
display adjustments, or who simply prefer not to adjust the contrast.
These contrast stretched images may help solve some of the problems
that some users encountered with getting the original images to look
the way they wanted. These new images have a much greater contrast when
compared to the originals. The drawback is that the stretch is "fixed",
so that you cannot recoup the original pixel values. With the original
set of images (GeoTIFF, MrSID, and JP2 formats), the user can achieve
the same type of contrast adjustment seen in the second set of imagery
and still make use of the full range of data values acquired by the
digital cameras.
Here are screen shots that
compare the same area in the original MrSIDs (with no stretch or
modification) and the contrast stretched imagery:
 Datalayer Description_files/coq05_csth.jpg)
To learn how to adjust the appearance of the original imagery to your liking, see the Display Options page.
Free Download
Images in the following formats are available for download as 4 km. × 4 km. tiles (based on the Ortho Index tiling scheme):
- MrSID, lossy, at 20:1 compression ratio, 3 bands (RGB). 10 MB each. Two sets:
- From original GeoTIFFs
- From contrast stretched GeoTIFFs
- JPEG 2000, lossy, at 16:1 compression ratio, 4 bands (RGB and IR).15 MB each. Two sets:
- From original GeoTIFFs
- From contrast stretched GeoTIFFs
Order (on CD and DVD)
Available by order only are:
- The original uncompressed, unstretched 4-band 4 km. × 4 km. GeoTIFF
tiles (based on the Ortho Index tiling scheme). 250 MB each.
- 4 km. × 4 km. tiles in lossless JPEG 2000 format
(compressed to 125 MB each but without any loss in image quality from
the original GeoTIFFs)
- Large regional mosaics in the MrSID format (based on the 2005 Ortho Mosaic tiling scheme). Two sets:
- From original GeoTIFFs
- From contrast stretched GeoTIFFs
- Large regional mosaics in the JPEG 2000 format (coming soon)
Users also may order the imagery available via download for regions (town, watershed, etc.).
Comparison of the 2005 Ortho Imagery products MassGIS distributes:
File Format |
Index Scheme |
Compression |
File Size per Tile |
# Bands |
Contrast Stretched |
How Distributed |
GeoTiff
|
OQ Tiles |
None
|
250 MB
|
4 (RGBN)
|
No |
Order |
MrSID
|
OQ Tiles |
Lossy (20:1)
|
10 MB
|
3 (RGB only)
|
No |
Free Download / Order |
OQ Tiles |
Lossy (20:1) |
10 MB |
3 (RGB only) |
Yes |
Free Download / Order |
Mosaic |
Lossy (30:1) |
Varies |
3 (RGB only) |
No |
Order |
Mosaic |
Lossy (30:1) |
Varies |
3 (RGB only) |
Yes |
Order |
JPEG 2000
|
OQ Tiles |
Lossy (16:1)
|
15 MB
|
4 (RGBN) |
No |
Free Download / Order |
OQ Tiles |
Lossy (16:1) |
15 MB |
4 (RGBN) |
Yes |
Free Download / Order |
OQ Tiles |
Lossless
|
125 MB
|
4 (RGBN) |
No |
Order |
Color Tone and Appearance Users should note that color tone
and balance are always based on personal preference. Image color processing
frequently involves a series of compromises with the overall objective
of providing images “with the appearance that people expect”. Different
hardware (monitor, video card, etc.), software, and subjective perceptual
differences can all contribute to the perception of color in these images. Datalayer Description_files/coq2005_4th.jpg)
In order to preseve as much of the raw data as possible, Sanborn and MassGIS chose to minimize any processing that might enhance the imagery, leaving such techniques (e.g., contrast and
brightness adjustment, etc.) to the user. For example, ArcGIS users may want to set the display properties for these images to "Resample during display using Bilinear Interpolation (for continuous data)" in the Properties
box, Display tab. (The Cubic Convolution display method may result in gaps between adjacent image tiles). Other options include adjusting the Contrast and Brightness settings on the Effects Toolbar or applying a stretch
(e.g. Standard Deviation) to the images in the Properties box, Symbology tab. When stretching the image, users may choose to base the stretch on the image as a whole, or just base statistics on the current display
extent (an option available at ArcGIS 9.1). Achieving results you like may require exploring the capabilities of your software and hardware, which can take considerable time. Printing or plotting the images further
introduces variability due to different hardware and software systems, etc.
Users should note that ArcMap will automatically apply a 2 standard deviation stretch to Tiff, JPEG2000, and ArcSDE formats of these images. This may result in a "too bright" appearance in some areas.
Users can adjust this default stretch to their liking. ArcMap will NOT automatically apply any stretch to the MrSID images, which may result in a "dark" appearance.
See the Display Options page to compare some different settings and learn how to best display the non-contrast stretched images.
Users may also observe a different appearance between the 2005 and 2001 color imagery. The two datasets were produced with different methods and have a significantly different distribution of pixel values (histograms).
Black 'nodata' Areas
The JPEG 2000 and GeoTiff versions of the imagery contain black (RGBN values of 0) pixels in parts of some tiles beyond the interpreted area just outside the state boundary or offshore. Users may want to display
these pixels as white (values 255,255,255) or as transparent. In ArcMap, go to the image's Layer Properties dialog, Symbology tab, check Display Background Value and click the color selector next to the 3 "0
0 0" textboxes to choose the desired background color. The MrSID files were processed so that all 0-value pixels were changed to 255.
Displaying in ArcView 3.x
For MrSID images, place the AVMrSID.dll
file in the BIN32 folder where ArcView is installed (e.g., C:\ESRI\AV_GIS30\ARCVIEW\BIN32). To display the JPEG 2000 images in ArcView 3.x, download and install the GeoJP2™ ArcView Plugin.
Image Catalogs Image catalogs are available for download for use with the MrSID and JPEG 2000 files. Users can load the following image catalog file into
GIS software instead of loading in each individual image; as you pan around and zoom in and and out, the catalog will automatically retrieve and display the image(s) for the
current geographic extent. Simply place the image catalog in the same folder on disk with the image files.
- coq2005hsid.dbf - MrSID tiles (may be used with original and contrast stretched images)
- coq2005jp2.dbf - JPEG 2000 tiles (may be used with original and contrast stretched images)
Note, however, that if using the image catalog in ArcMap, you will not be able to change symbology characteristics such as stretch type; these types of image enhancement
are accessible only from the Layer Properties Symbology tab, which is not present for image catalogs. However, the appearance may be affected, to a lesser extent, by adjusting the Contrast and
Brightness settings on the Effects toolbar. See more details on the Display Options page.
Displaying with Feet-based data Users may successfully display our meters-based imagery in ArcView 3.x with other data in NAD83 Mass. State Plane feet
simply by changing the accompanying .sdw or .j2w "world" files and installing the newest version of the file AVMrSID.dll.  Datalayer Description_files/coq2005_6th.jpg)
The process is as follows: Open the .sdw or .j2w file in a text editor and multiply all values by 3.2808333316 and save.
If users wish to display the images with feet-based (or any non-meters-based) data in ArcMap, add the image file (.sid or .jp2, ensuring it is stored in the same folder with the companion .aux file) and
the data (if it has a .prj file, indicating a defined spatial reference for vector data) and the images will project on the fly (ArcMap does not use the .sdw or .jp2 world files).
Black areas in ArcView 3.x If users experience black areas adjacent to the mosaics in ArcView GIS 3.x, make the image
themes active, choose Theme > Properties, and select 'display' from the 'Extent Limit' dropdown.
Near infrared "expected" red/green look
To achieve the conventional red/green look (with red indicating vegetation and green representing impervious surfaces like pavement and rooftops) when displaying the fourth (near
infrared) band, display bands 4, 2, and 1 for the red, green and blue channels, respectively. The fourth band is available in the GeoTIFF and JPEG 2000 formats, not MrSID. In ArcGIS, go into the raster layer's
Properties > Symbology tab and show the raster as an RGB composite and assign the bands to the channels. Then choose Stretch Type of 2 Standard Deviations.
The datalayer is maintained by MassGIS. Additional information concerning the technical details of the project may be available upon request.
For other ortho image data available from MassGIS, see the following datalayers:
Please note that MassGIS does not have any aerial photographs prior to 1992. For information on such products please see
http://erg.usgs.gov/isb/pubs/factsheets/fs12796.html.
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