Initial Release: New Statewide Aerial Imagery for Fall 2018, Winter 2018/19, and Spring 2019.

The Rhode Island Department of Transportation has contributed three new statewide aerial imagery collections to RIGIS! They consist of:

All imagery are 3-band, true color, with a spectacular 3-inch spatial resolution. They are currently accessible via both ArcGIS image services and hosted ArcGIS Online tile layers via the URLs listed above.

Traditional file download for these image collections is expected to be made available in Fall 2019, after a new web server is installed and configured on behalf of RIGIS.

The images were collected and processed using a new imaging technology at a significant cost savings. These are not traditionally orthorectified aerial photographs. You will encounter blending issues, building lean, shadows, and other artifacts. The horizontal accuracy of these images has not been assessed; on casual observation it seems to vary throughout the state. Relative measurements (e.g. the length of a football field, or the footprint of a building) should be quite good. The capture dates for specific images cannot be determined.

As is the case with all RIGIS data, users are strongly encouraged to carefully evaluate the suitability of these data for their particular needs.

Related blog posts:

Important Security Update

PRIORITY:  TLS 1.2 security implementation will be enabled April 16, 2019.

From Esri Technical Support:

As part of improving ArcGIS Online security, Esri will require TLS 1.2 connections for ArcGIS Online services starting on April 16, 2019. Esri software that connects to ArcGIS Online will be affected by this change. To ensure continued access to ArcGIS Online services, you must take action prior to the implementation of TLS 1.2.

Important Information from Esri:

Esri Software Products Affected by TLS 1.2 Implementation

Important Updates for the ArcGIS Platform and Transport Layer Security (TLS) Protocol Support

Coordinate Systems Supported by RIGIS

The standard coordinate system used by RIGIS is Rhode Island State Plane NAD83 U.S. Survey Feet (EPSG 3438). Nearly all datasets distributed by RIGIS use this coordinate system, and this is the coordinate system we use behind the scenes to manage and archive these data.

However when RIGIS migrated its data clearinghouse to the Esri ArcGIS Hub, we began supporting a second coordinate system for our vector datasets: WGS84 (EPSG 4326). By introducing support for this coordinate system, vector datasets distributed by RIGIS are now easily used by software such as Google Earth Pro.

How do you know what coordinate system is used by the dataset you’ve downloaded from RIGIS?

  • If you downloaded the vector dataset using the “Full Dataset” or “Filtered Dataset” download option, then it uses the WGS84 coordinate system.
  • If you downloaded the vector dataset using the link to the source RIGIS dataset listed under the “Additional Resources” download option, then it most likely uses Rhode Island State Plane NAD83 U.S. Survey Feet.
  • Ultimately you should always review the metadata. All data distributed by RIGIS is delivered with documentation – or metadata – that includes a description of its coordinate system.

Technical background note: RIGIS does not permit downloading data using the Rhode Island State Plane NAD83 U.S. Survey Feet coordinate system using the “Full Dataset” or “Filtered Dataset” download options. There are two reasons for this:

  • Offering data with the WGS84 coordinate system opens up RIGIS data to a much broader audience. Many free GIS data viewers simply do not support RI State Plane, or do not support projecting from RI State Plane to other coordinate systems.
  • The Esri technical support staff we’ve interacted with to date have not known what datum transformation is used behind the scenes to convert between these two coordinate systems.

What about the upcoming NGS release of the new geometric reference frame and geopotential datum in 2022? RIGIS has followed NGS recommendations by maintaining thoroughly documented metadata records whenever possible. We occasionally monitor the development of transformation tools and will certainly consider migrating data distributed by RIGIS to the new reference frame in the future.

Don’t Need it All? Try Filtering!

At times you may not need to download an entire GIS dataset. For instance, the contour line datasets available from RIGIS are quite large and can be slow to draw on your screen.

The RIGIS data clearinghouse gives you the option to download a portion of a dataset. You can do this by using the filter tools.

Note to desktop GIS users: RIGIS datasets cannot be subset via clips, intersects, etc, via the website. However try adding these a RIGIS feature service to your next desktop GIS project, and then running these tools! You’ll be pleasantly surprised.

To filter a dataset using a table on the RIGIS data clearinghouse, first head over there:

Find a dataset you’re interested in working with. In this case, I’ve chosen RIDEM’s Local Conservation Lands dataset.

Choose the “Data” tab to open up a tabular data view.

Try filtering this dataset! Click the small Filter icon to the left of the “Site Name” column heading.

A small window should have appeared at the top of the table. Choose the small arrow on the right-hand side of this window to open up a new box that you may type in.

Start typing in a name, such as “Valley Falls”. Both the table and map will update to list the records that have a Site Name that starts with the keyword “Valley Falls”. You should have only one record in your table now – Valley Falls Heritage Park. You’ve successfully filtered this dataset!

Try downloading this filtered dataset. Look for the “Download” menu on the right-hand side of the page, and select it.

There is a “Filtered Dataset” section within the Download menu. Choose one of the options, such as a KML file that’s compatible with Google Earth. When you open this file, you should fine just one record representing Valley Falls Heritage Park in Cumberland, RI.

KML and RIGIS Vector Data

Most of the vector GIS datasets (e.g. roads, land use, benchmarks, etc.) distributed by RIGIS are accessible via KML. KML is widely supported by mapping software and apps such as Google Earth and Esri ArcGIS Earth.

These KML linkages are readily available from most of the RIGIS vector dataset description pages.

Head over to the RIGIS data clearinghouse:

Try browsing through the different data categories, or try the search bar to find the dataset you’re interested in. In this example, we’ve searched for the keyword “911” to find the RI E911 road centerline dataset.

Look for the “Download” menu on the right-hand side of the page.

If you click on it, you’ll see a list of options. Under the “Full Dataset” section, choose “KML”. This will download a KML file containing this dataset straight to your computer or mobile device.

Depending on your configuration, the KML file may open automatically in your mapping application, or you may need to head into your application to add the KML file manually.

KMZ and RIGIS Aerial Photos

RIGIS supports the use of KMZ files to access many of its aerial photograph collections! The KMZ file format is widely supported by mapping software and apps including Google Earth and Esri ArcGIS Earth.

We’ve recently updated our website to make these KMZ linkages easier to find. NOTE: Note all RIGIS image collections are currently available as KMZ.

Get started by heading over to the RIGIS data clearinghouse:

Scroll down on the homepage until you find button for the RIGIS Imagery Collections.

Select the aerial photo collection you’re interested in viewing, such as these from Spring 2011.

Finally, choose the KMZ option from the list to start the download.

Depending on how your computer or mobile device is configured, your software may automatically open, or you may need to open the KMZ file within your software.

When to Choose an ArcGIS Image Service vs an ArcGIS Online Hosted Tile Layer

The most recent RIGIS orthophotos from Spring 2018 are available as two different types of online services: two different ArcGIS image services and one ArcGIS Online hosted tile layer. Why choose one service over the other?

Choose one of the ArcGIS image services if you need any of the following:

  • Ability to zoom into map scales larger than 1:256.
  • Highest possible print quality.
  • Ability to change the appearance of the images, such as applying a different type of stretch or brightness values.
  • Compatibility with open source GIS software that requires WMS or WCS protocol.

Use the ArcGIS Online hosted tile layer if:

  • You have a need for speed. The ArcGIS Online hosted tile layer will likely draw more quickly than the image service.
  • You need to work offline using ArcGIS Collector.
  • You don’t mind not being able to zoom into map scales larger than 1:564.
  • The image services are inaccessible due to maintenance, etc.

Spring 2018 Aerial Photos: Initial Release

Spring 2018 aerial photographs are now available from RIGIS as ArcGIS image services and an ArcGIS Online hosted tile layer! Here’s a quick rundown:

Esri ArcGIS Server Image Services (a.k.a. “Imagery Layers” according to ArcGIS Online) directly hosted by the URI Environmental Data Center are available in two different coordinate systems.

Web Mercator WGS 84 Meters:

Rhode Island State Plane NAD 83 U.S. Survey Feet:

There is also an ArcGIS Online Hosted Tile Layer is exclusively available in Web Mercator WGS 84 Meters:

This is the first of nine orthophoto acquisitions under this contract that are planned for calendar years 2018, 2019, and 2020 in spring (leaf-off), summer (leaf-on) and fall/winter (leaf-off).

More details are forthcoming after the documentation (metadata) is squared away. Individual image tiles will also be made available for traditional download via RIGIS after the metadata record has been completed. Keep an eye on this blog or the RIGIS-L email listserv for future announcements.

Interested in learning more? Consider attending the Rhode Island Pictometry User Group coming up at Rhode Island College on December 19, 2018. More information, including registration information for this free event, is available from EagleView.