Friday, May 22, 2009

ArcPad Tips & Tricks #5: Choosing the correct image format

ArcPad supports a number of different image formats, including BMP, GIF, JPEG, PNG, TIFF and ECW (note that you require a 3rd party extension to use ECW images). But how do these differ? And which one should you use? There are a couple of good summaries on the ArcPad Team Blog which should help you get started.

The long and the short of the matter is you have to make a compromise between image file size and drawing performance. Obviously, the larger the image is, the more storage you need available on your device to save the image. If storage is an issue, then it is worth looking at one of the compressed image formats, such as JPEG or ECW.

Whilst compressed images save on storage, they do require more overhead when viewing in the map. ArcPad must decompress and interpret the image, as you pan and zoom around the map, resulting in poorer performance. This is of particular importance in ArcPad 8, given some of the memory issues that users have been facing.

In very simplistic terms, the following table summarises the differences:

For more information, refer to the ArcPad Team Blog articles.

Thursday, May 21, 2009

ArcPad - A Field Users Guide

ESRI have a great additional ArcPad Resource on their site.

For guidance on how to use ArcPad in your field GIS project, take a look at Johnathan Raper’s, PDF ebook, 'ArcPad A Field User’s Guide'.

The book can be found here.

Please note that the book is based on a previous version of ArcPad, however the components and principles as discussed in the book are still valid.

Wednesday, May 6, 2009

ArcPad Tips & Tricks #4: Optimising Streetmap Extension

We have had a few enquiries from customers using the Streetmap Extension with ArcPad 8. On some PDA's, they are unable to add the streetmap data to a map that already has layers in it. If the map is empty, then there are no issues. To confuse things further, it all loaded fine on the desktop version of ArcPad.

After a bit of investigation, it turned out that the cause of the problem was memory constraints. The only way that we could get the data to load was to turn off all extensions that were not being used. Once we had ArcPad down to the bare bones state, the data loaded up fine, and the extension could be used.

So, to turn the extensions off:

  1. From the Options menu, select Utilities à Advanced Settings
  2. Switch to the Extensions menu
  3. Uncheck all extensions that you are not using. By default, a lot of these will be already turned off. There should be some (such as the graphics layer and photo layer) that you can also turn off.
  4. Restart ArcPad (this is important, as the changed settings are not applied until you restart).

If you are still having problems, then you may need to clip a subset of the streetmap data to restrict the amount of data in the map.

Tuesday, May 5, 2009

ArcPad Tips & Tricks #3: Related Table Support

There has been a little bit of confusion from some of our clients surrounding the support of related tables within ArcPad, using the AXF file format. Here are some basic rules which should help to clear things up:

  1. One-to-many, and one-to-one relationships are supported. Many-to-many are not.
  2. Related tables must be just that, tables, and not feature classes.
  3. The parent in the relationship must be a feature class (point, line or polygon). This is in keeping with the map-centric focus of ArcPad, where all editing is done via the map.
  4. You can relate as many tables to the base feature class as you like.
  5. You must have a Geodatabase relationship class set up in order for a related table to be exported. Any joins or relates that you set up within your ArcMap mxd document will not be exported.

Related tables are an extremely useful tool to have out in the field, as they eliminate the need to duplicate spatial features that define the same location in space. For example, you may have a tree / inspection (one-to-many) scenario. Without related tables, each time you do an inspection, the location of the tree would have to be recaptured, when in fact it probably hasn't moved. Over a period of time, you will end up with a whole heap of points stacked on top of one another. With related tables, you would only collect one point – that on the initial inspection. From then on, only tabular data is collected. This leads to significant performance improvements also, as fewer features have to be drawn.