Issues and Expectations of Using the 2005 Orthophotography with Your Existing GIS Data
What is data swim?
Well, it has nothing to do with water. If you have existing GIS data, you may find that your line and point maps (vectors) no loner line up on the right place on the photo. Why? What’s going on here?
When a vector or point dataset is originally created by digitizing over existing photography or another source, it will be as accurate as the original source data. The accuracy of original source data varies dramatically among different communities in Indiana. The 2005 orthophotography is highly accurate, therefore less accurate vector data might not line up correctly on the photos. Even where high accuracy source data do exist, some minor variations should be expected from year to year (see Figure B). This is referred to as “data swim,” or the effect of the vectors swimming from photo to photo.
In another example, data that were collected using high accuracy techniques – like GPS, map or survey grade – may be more accurate than previously available source data. If your point data was corrected or moved to line up on less accurate photos, once you start using the 2005 orthophotos the points might not show up in the right place.
The 2005 orthos are highly accurate – users can be very confident in their reported accuracies.
What does this mean for my local GIS?
If I move my vector maps to align to the new photos won’t I just have the same problem next time?
Not really. Here’s why: The acquisition method used for the 2005 orthos also collected a highly accurate elevation model at the same time the pictures were taken. Elevation models are used to correct distortions (or “orthorectify”) the aerial photography. This elevation data is part of the deliveries to all counties as part of the project. Future orthophotography projects, whether done as a statewide project or by a local community, can be tied to this high accuracy elevation model and result in ortho updates that closely match the 2005 ortho accuracy. The result will be minimum data swim in future years. In this way, the 2005 Statewide Orthophotography Project will provide benefits for years to come.
Note that vector data of known high accuracy (like good GPS data) should not necessarily be moved to fit a lower accuracy orthophotography base!
When will the orthos be available?
Data from the 2005 Orthophotography Project will be delivered to all counties by March 30, 2006. Each county will receive datasets as they are completed and accepted by the State.
WE REGRET THAT THE DEADLINE FOR COUNTIES TO PARTICIPATE IN THE BUY-UP PROGRAM HAS PASSED. THE INFORMATION BELOW IS INCLUDED HERE FOR REFERENCE ONLY.
What are “buy-up” opportunities?
The Orthophotography Project has �cafeteria style” buy-up options that would allow a county to purchase additional products/options (such as higher resolution) at reduced costs.
How much grant money will my county receive?
Each county will receive a set aside grant to purchase updated orthophotography that meets a consistent statewide standard. To use the funding, counties can participate in a statewide memorandum of understanding (MOU) for the orthophotography program. Click here for a listing of the set aside grant award by county, along with cost estimates for counties desiring to buy-up for additional products/options.
How much will it cost?
Counties have had buy-up cost estimates since May 2004 and should be anticipating their commitment. Please consider using the cost estimates that have been provided, but keep in mind THESE ARE ONLY ESTIMATES. Budgets will be provided with the formal request for commitments, and a final cost will be provided upon close of contract negotiations.
How was it determined how much my county gets?
Cost estimates per square mile were used to calculate the grant amount each county would receive.
When do we have to commit?
On October 27th, 2004 the State will issue a formal request for commitments from counties wishing to participate in the buy-up program. There will be approximately 2 weeks for counties to return a formal commitment to buy-up prior to signing a contract. The State recognizes the timeframe will be tight. This is because vendor proposals (due October 26) will give a more concrete budget to counties, and the State must define a complete scope of work (i.e., buy-ups) before final contract negotiations can commence.
COUNTIES ARE ENCOURAGED TO START THE COMMITMENT PROCESS TODAY. Counties can start the commitment process today by gaining approval for buy-ups during your upcoming commissioner meetings.
How does our county apply for this funding?
County Emergency Management Directors must apply for the Indiana 2004 State and Local Homeland Security Grant. However, the orthophotography program is a set aside � counties do not need to apply separately.
What will the State contract look like?
Over the coming months, the state will enter into contracts for the 2005 Orthophotography Program at agreed pricing per county with pre-qualified vendors for orthophotography services, project management, quality assurance and acceptance testing.
How does this benefit my county?
Counties will benefit from:
- Current color imagery, taken during the Spring 2005 leaf-off season.
- Seamless base map with neighboring jurisdictions access to neighboring counts data for mutual aid response.
- High resolution detail in the 30 most populated counties (1-foot or better), good resolution in less populated counties (1-meter or better).
- Easy to purchase off of state contract technical specifications pre-defined.
- Cafeteria-style “buy-up” options available for higher resolution, color infrared, and elevation data.
- Digital surface model for 3-dimensional mapping.
- Multi-use base mapping (e.g., local communities can use orthophotography for emergency management, drainage, planning, law enforcement, property management, etc.)
- Public-domain data that can be used for other government and business needs in your county.
How much does my county save by participating?
We”ve estimated the total cost savings to be 20-40% over each county going it alone, plus savings due to the matching grant dollars. Counties can save tens- to hundreds-of-thousands of dollars over their last orthophotography update. This savings includes your time/expense not needed for the procurement process and project management.