Pdub,
I use Delta Geomatics, Gary Hubley, in Santa Rosa and have been very satisfied with their product over the last 15 years. Give them a call and tell Gary hello for me.
http://www.deltageomatics.com
Mike Ford
Photogrametrists(sic?)
-
Steve Martin
- Posts: 632
- Joined: Mon Apr 04, 2005 12:24 pm
- Location: Hayward
Plan, then review
Whichever firm you end up going with, I would suggest doing some of the flight planning on your own to get an idea of the expected accuracy going into the project. You can discuss options and costs with the photogrammetrist. What you do not want to do is sacrifice adequate checks for overall costs though as errors in the base topo can be quite costly to fix in construction.
I always include checks into the mapping process, for example: setting additional premarked control points and hold back the coordinates on a couple of them. I'll ask that the Photogrammetrist read off these control values in the AT process to make sure their setup is correct before they start mapping. After verifying they are within specification, I'll give them the survey values to include in the final AT adjustment.
I also ask that the Photogrammetrist provide model setup reports so that I can see how much they are letting my control valuse float to get the model to set up.
Then, I have the survey crew collect a representative sample of topo shots on the project to check against the DTM provided by the Photogrammetrist. This will give a true picture of the accuracy of the mapping as opposed to the theoretical.
I do have the survey crew do a walk thru of the project with the draft map in their hands to see if any utilities were missed and that the contours make sense. Labeled spot elevations in the draft map can be staked out and compared against the map value.
This may seem like a lot of checking, but change orders for changed conditions on a large construction project can cost so much more than doing a few checks.
I am thinking about a large dam project, for which the mapping was not prepared under my supervision, where an experienced surveyor just standing on the site and reviewing the map could have caught a big omission by the photogrammetric company.
A lot of aerial mapping problems can be caught early by including checks and careful review into your process.
I always include checks into the mapping process, for example: setting additional premarked control points and hold back the coordinates on a couple of them. I'll ask that the Photogrammetrist read off these control values in the AT process to make sure their setup is correct before they start mapping. After verifying they are within specification, I'll give them the survey values to include in the final AT adjustment.
I also ask that the Photogrammetrist provide model setup reports so that I can see how much they are letting my control valuse float to get the model to set up.
Then, I have the survey crew collect a representative sample of topo shots on the project to check against the DTM provided by the Photogrammetrist. This will give a true picture of the accuracy of the mapping as opposed to the theoretical.
I do have the survey crew do a walk thru of the project with the draft map in their hands to see if any utilities were missed and that the contours make sense. Labeled spot elevations in the draft map can be staked out and compared against the map value.
This may seem like a lot of checking, but change orders for changed conditions on a large construction project can cost so much more than doing a few checks.
I am thinking about a large dam project, for which the mapping was not prepared under my supervision, where an experienced surveyor just standing on the site and reviewing the map could have caught a big omission by the photogrammetric company.
A lot of aerial mapping problems can be caught early by including checks and careful review into your process.
Steve Martin, LS 7264