NEW Vermont Orthos Available for Rutland & Windsor Counties!

May 14, 2012

Leslie Pelch, VCGI

The first installment of the THIRD vintage of digital orthophotos of Vermont is available for free download!

Covering roughly Rutland and Windsor counties, the new imagery has the following characteristics:

  • ¬†.5 meter pixels (same as Orthophotography collected by VT Mapping Program until 2009)
  • A set of color images with near infra-red included (CLRIR) and a set of black and white images ( PAN) will be available (previously only black and white was available)
  • Accuracy is expressed as follows: The horizontal accuracy of the orthorectified imagery shall meet or exceed a verified ASPRS Class I horizontal accuracy of +/- 1 meter RMSE (for both X and Y) for 50cm ground sample distance imagery and 2.44 meters at 95% confidence level according to the NSSDA standard methodology.

The VT Imagery Program “News” page has links to an FAQ about the imagery as well as where to download:

http://www.vcgi.org/dataware/default.cfm?page=./image_library/vip_info/vip_news.cfm


FOSS4G North America 2012

May 9, 2012

Bill Morris, Geosprocket, LLC.

I had the good fortune to make it to this year’s iteration of the Free and Open Source for Geospatial (FOSS4G) tech conference – North American edition (other sections of it will be occurring in Germany and China). Having missed the O’Reilly festival of place, it was a great opportunity to catch up with – as one attendee put it – “The real makers in the world of map ” …. While there was more afoot than I could ever have followed entirely, I took note of two items… Click here for more: http://geosprocket.blogspot.com/2012/04/foss4g-north-america-2012-noted-points.html


Statewide 10 M DEM and Derivatives Available

May 2, 2012

Mike Brouillette, VCGI

VCGI is happy to announce the release a new 10m statewide DEM and derivative layers from the recently completed (Jan. 2012) statewide 1/3 arc-second (~10m) DEM from the USGS National Elevation Dataset (NED). The NED is a multi-resolution dataset so for areas where LiDAR data exists the vertical accuracy is higher and subsequently the derived contours won’t match the 7.5′ USGS Quad Contours very well. See the Abstract section of ElevationContours_CN20T for more on this issue.

While the layer ElevationContours_CN20T can be custom downloaded, e.g., “clipped and zipped”, the other datasets are statewide in extent and compressed to “zip” files due to their size. These zip files contain both metadata and layer files you can elect to use in ArcGIS.

NEW LAYERS:

  • ElevationDEM_DEM10m (342 Mb) – 10m DEM
  • ElevationContours_CN20T (990 Mb) – 20′ contours
  • ElevationOther_ASPECT10m (358 Mb) – Aspect identifies the down slope
    direction of the maximum rate of change in value from each cell to its neighbors. Values rounded to nearest Integer.
  • ElevationOther_HILSH10m (299 Mb) – Hillshade from 315 degree
    azimuth and 45 degree altitude
  • ElevationSlope_SLOPE10m (135 Mb) – Reclassed “percent rise” slope
    values rounded to nearest integer.

DATA ISSUES:

  • USGS states the NED can be used for hydrologic modeling but VCGI
    has not conducted any verification. It is highly recommending you review this issue before investing substantial resources in a modeling project.
  • WaterHydro_VHD – These features are based on the earlier black and
    white Orthophotos (1994-2000), and will not necessarily match up with the 10m DEM or the latest vintage of Orthophotos (2005-2010).
  • VTHYDRODEM – Created in 2004, this VT “hydrologically enforced” DEM
    (using the local resolution NHD for VT, i.e., the “VHD”) was interpolated from the VT Mapping Program orthophoto rectification X, Y, Z points to support the NHD effort and creation of “WaterHydro_VHDCARTO”, a cartographic version of the NHD with “intermittent” and “perennial” modeled streams. Having created it and working with ElevationDEM_DEM10m I would say the latter is more accurate. However, this raster does have the advantage of being integrated with the VHD.
  • ElevationContours_CN100T and *_CN50T – These are not currently based on the 1/3 arc-second NED and will be replaced sometime in 2012. Until then they will not be coincident with *_CN20T.

The following pre-existing contour data will be superseded by ElevationDEM_DEM10M

  • ElevationContours_CN20T06A 20 ft contours from Ortho DEM – Addison, Wash, Orange Cnty
  • ElevationContours_CN20T06B 20 ft contours from Ortho DEM – Rutland & Windsor Cnty
  • ¬†ElevationContours_CN20T07 20 ft contours from Ortho DEM – Chit, Lam, Caledonia Cnty
  • ElevationContours_CN20T08 20 ft contours from Ortho DEM – GrandIsl, Frank, Orlean Cnty
  • ElevationContours_CN20T09 20 ft contours from Ortho DEM – Essex Cnty

Please feel free to contact me directly with questions, feedback about the metadata and any content or grammatical errors: mikeb@vcgi.org