Frequently Asked Questions
Do you have an aerial map of my site?
Many people, even professionals, confuse aerial photographs with maps. Because of our longevity, and aggressive speculation program, Col-East has developed a large library of existing aerial photography. This photography is intended to be used to develop photogrammetric mapping but is available for use by anyone. If your site is within our coverage area we most likely have a photograph available. Mapping is developed on a custom basis and is owned by the individual or firm who paid to have us map it. We cannot distribute existing mapping without the clients' permission.How can I find out if you have coverage of my site?
You may search the coverage listing to determine if the town your parcel is located in has been covered and when.Ideally you would fax a locus of the site to us, at 413 663-3489, including any limitations for the requested photography, i.e. maximum or minimum scale, date(s), etc. We will search our library and call or e-mail you with our results. There is no charge for this service unless you decide to purchase.
What scale is this photograph?
Our coverage listing shows the nominal negative scale for each project. This will be an approximate scale, based on the mean terrain within a particular project. The actual scale of any individual negative may well be slightly different than the nominal scale and may, in fact, vary across the negative due to tip, tilt and/or relief.A photograph is a perspective view. It is subject to distortion due to displacements of the camera from the vertical (tip and tilt), lens factors, and relief. Please see the discussion of orthophotos for further explanation of the difference between a photograph and a map.
Why don't you have color? Why is color so expensive?
Our photo library contains relatively few color exposures. There are several reasons for this. (1) Color film is expensive, about twice the price of black and white. (2) While we process all of our own black and white photo product we out-lab our color work because we do so little of it. This translates into higher costs and more delays. (3) Color film has three layers of emulsion vs. one layer for black and white. This translates into crisper edges in black and white and a "clearer" image. Black & white film is generally better for mapping.Can I see my neighbors fence?
The actual resolution of a particular negative depends on many factors, such as emulsion, atmospheric conditions, and camera type. Some generalizations may, however, be made:At 1:30,000 (1"=2,500') you will see roads, railways, rivers, wooded areas and larger buildings. Small buildings and individual trees will likely not be visible.
At 1:10,000 (1"=830') individual trees, stone walls (but not wire fences), clumps of shrubbery and utility poles are visible.
Most of our existing library is at 1:6,000 (1"=500'). At this scale you will clearly see white pavement markings and features as small as fire hydrants and catchbasins. Most manholes will be visible, but not all. Fences will be recognizable by type.
Your photo listing says you can map my site at 1"=40'/2' CI, but can you map 1' contours?
Our photo coverage listing includes a column entitled "Suitable For". The numbers in this column indicate the largest scale and smallest contour interval to which we will guarantee meeting National Map Accuracy Standards (see above) for mapping collected using this photography. Map accuracy depends on many factors, including negative scale, control distribution, density and accuracy, map collection equipment and the skill of the operator.Yes, we can plot one-foot contours from 1"=500' photography. We will not, however, guarantee meeting NMAS for a one-foot contour.
What is an orthophoto?
Orthophotos combine the image characteristics of a photograph with the geometric qualities of a map. They serve a variety of purposes, from interim maps to field references for Earth science investigations and analyses. The digital orthophoto is useful as a layer of a GIS and as a tool for revision of planimetric and topographic maps.Unlike a standard aerial photograph, relief displacement in orthophotos has been removed so that ground features are displayed in their true ground position. This allows for the direct measurement of distance, areas, angles, and positions. Also, an orthophoto displays features that may be omitted or generalized on maps. But requires the user to interpret them.
I don't use AutoCADŽ. Can I use your mapping?
Most CAD software will accept .DXF files. Some softwares may require special treatment for complex linetypes like guardrails, treelines, etc. We can supply a sample drawing to test your ability to translate. We can also provide custom ASCII, etc. file formats.I use MicrostationŽ. Can I use your mapping? Can you give me .DGN files?
While we have translators to deliver .DGN files we no longer have the ability to use MicrostationŽ to perform quality control inspection of the .DGN files. Recent releases of MicrostationŽ accept .DWG files and we recommend this path as we are very sure of being able to achieve the desired format in AutoCADŽI need more than one negative for my site, can you put more than one photo together into an image?
This involves the process of mosaicking. The traditional photo mosaic involves printing the required contact prints covering the site, cutting and splicing them together and shooting a new negative of this assemblage. This mosaic negative is then used to print enlargements. Borders and titleblocks can be added and important features can be labeled.Photo mosaics have a number of problems. Firstly, the enlarged mosaic is three generations removed from the negative. This results in image degredation (fuzzyness). Secondly, the imagery is not rectified and thus, unless the ground is perfectly flat and the camera was perfectly vertical, the seams between exposures will not match up perfectly. Some continuous features will not appear continuous. Thirdly there will be tonal variations between exposures and flight lines because the light is arriving at the camera from different angles.
Given these limitations, however, we can compose and print mosaics on paper or mylar. The price will vary according to the number of exposures required. Please contact us for a quote.
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