As most of my followers on Twitter already know, I’ve been playing around with my new toy the last couple of weeks: a Trimble Juno SB GPS, running ArcPad 8. So far, I am very happy with my decision to buy this unit. It has been some work to get to know the ArcPad software, and there are a few things I think it will do, but haven’t figured out yet. However, I am surprised at how much it can do. The Juno and ArcPad have both exceeded my initial expectations.
How can I use NYS Orthophotos in ArcPad?
In my GIS work, I make extensive use of the NYS orthoimagery supplied through the NYS GIS Clearinghouse website. I want to be able to use these aerial photos during my fieldwork. The orthophotos are supplied in MrSID format, and can be easily added to an ArcMap document using the supplied Raster Catalogs. But here’s the problem: ArcPad can read MrSID rasters, but cannot make use of the Raster Catalogs.
The individual MrSID tiles use an arcane naming system. This system is great for organizing them in a database, and to be read by a computer, but very difficult for a human being to decipher. Here’s a screenshot that shows the naming convention:
How do I decide which tiles to load into ArcPad?
The naming system makes it nearly impossible to decipher which tiles I need to load onto the Juno in order to use them in ArcPad. I could load all of the MrSID files onto the Juno, but that would mean transfering over 300 MB of data onto my microSD card over a USB cable; a little time consuming. So, how do I decide which tiles to use? I don’t. Here’s what I’ve decided to do:
- Load the entire Raster Catalog for the area I want to work on into ArcMap. (this typically includes an entire town’s worth of ortho’s)
- Set the coordinate system in ArcMap to match the ArcPad project you will use (typically WGS 1984)
- Zoom into the specific area I want to load into ArcPad (the extent of my field work area)
- Export the map as a JPEG image (making sure I use the Write World File option)
- Copy the JPEG image and World File onto my GPS unit, and load it into my ArcPad project
Here are a couple of screenshots of the imported JPEGs:
This aerial photo covered an area of ~6 square miles. At a resolution of 300 DPI, the JPEG output was ~6MB in size.
I hope this information is useful to somebody else. I’ve read through the ArcPad documentation, and have been searching through forums and blogs, but have not run across this procedure anywhere else yet. I intend to do some more tests using higher resolution orthophotos, higher DPI JPEG output, and other output formats. I’ll let you know how I make out in future posts. If anyone else has a better solution than this, please let me know. I’m always open to suggestions.