Application Notes

This document will come a collection of ideas for using a palm and gps together that are not necessarily obvious or perhaps require some explanation. This is intended to go beyond the obvious navigation uses of showing your location on a map. The first one is targeted at using your gps and palm as a field notebook to gather data.

TOC

Pros and Cons for using a gps and palm together

Pros

There are a number of reasons folks combine the power of the palm with a gps receiver. The most obvious is that the receiver they purchased doesn't have any display capability and you must buy a display. What isn't quite so obvious is the folks that use a standard consumer gps with its own display and the Palm together. Why bother?

  1. You will have Multiple display outputs showing several different things at once.
  2. The Palm offers a larger screen display than most handhelds.
  3. The availability of many gps programs and additional capabilities not available from the gps manufacturer.
  4. You are not locked to only support from the gps manufacturer. More choices.
  5. Other general purpose programs can be used on the palm to augment gps usage.
  6. Lower cost of 3rd party tools, maps etc.
  7. Additional memory available to extend unit recording.
  8. You can remote mount the unit for better sky visibility when needed.
  9. Palm programs support the ability to scan in your own maps.

I recommend a gps unit with its own display for use with the palm for many of the reasons mentioned above and because you may want to use the gps by itself on occasion when it is not convenient to carry both. The main negative for this solution is the need to have two units and the cable. There are hardware solutions that solve this. See my hardware page. Another advantage of the standalone gps receiver is that it will continue to collect data when you switch programs on the palm or turn the palm off. Otherwise you need to keep the palm running one program to ensure complete logging or trip data if you need it.

A card or attached solution such as gps companion can make the pilot seem like a standalone gps solution and provides most of the benefits. The only disadvantages are two sets of batteries and you have to remain in one program to collect log or trip data on all of the attached units I have seen. This should not be a problem if the program you are using has all of the screens you want. There are some visor units that use the visor batteries but two AAA cells won't run a gps and a visor for very long.

Cons

Here are a list of the negatives in using this solution

  1. Using two sets of batteries can be a drain (pun intended).
  2. A palm has a glass screen so it is not as rugged as standalone gps devices.
  3. While there are a lot of programs available they do not work together and so far no single one of them provide as much funtionality as a standalone gps.
  4. Switching between programs can cause a loss of data such as track logs or trip meters.
  5. The palm is not waterproof - but then neither are some gps receivers. This can be solved with a plastic bag such as aquapac or Eastman or perhaps an inexpensive ziplock bag.

Palm and GPS used for gathering information in the field

It seems that folks have begun to realize that the palm and the a gps can be used effectively together to gather field data for analysis later. I have received several requests for information on this subject so I thought I would devote a page to just this task. It is a natural extension of two great tools and a good fit for palm devices.

So far I have seen a few tools available for this task. These include (in no particular order):

Obtaining suitable raster maps

The primary method of obtaining raster maps for your palm is to use a scanner and scan in a paper map. Then you would use a program supplied with the mapping program or separately from the mapping program software vendor to convert the map for use on the palm. You can, of course, scan any paper map you wish but some are more useful for gps use than others. For example a standard road map is of limited usefulness. This is because it was never intended to be accurate from a gps perspective. Roads are often moved a bit to make room for names and there is no need to ensure that the map is to an accurate scale or that the top is true north. However if the map is not detailed and is only providing general location information it may still be useful if you can overcome the problems in getting it calibrated. Better sources for road maps are often an atlas especially if it includes lat/lon lines, but the projection is a concern. If the projection used results in curved latitude lines and longitude lines that are not parallel (a conic style) then it is not very suitable for gps use on the palm since calibration assumes the lat/lon lines are straight and parallel.

Good maps to use are those that already are designed for lat/lon use. These include topo maps, marine charts, and aviation charts. Generally a scan of one of these can result it very accurate and useful maps. Be sure that you save the scanned map in a format that can be used by the program you will be using to convert the map. Standard formats include Microsoft bitmaps, gif images, png images, and jpg images. Of these formats the jpg images are the least desirable since the compression format tends to blur text and lines just a bit. Microsoft bitmaps result in the largest images on the disk but this may be reduced somewhat by reducing the number of colors.

Other souces of maps include digital maps that may be available via the web. These map images can generally be downloaded and converted for palm use. The main problem lies in getting them calibrated. In some cases the software vendor may provide a source of precalibrated maps. Another source of precalibrated maps is GPSS. This is a raster map program for the pc but the maps can be converted for palm use and a secondary file is provided that includes the calibration data.

Raster Map Calibration

All of the palm programs provide for calibration using two locations. One in the upper left and one in the lower right. In some programs this can be done on the pc and in some this is done on the palm while some permit both. For pc calibration the exact corners are used while on the palm you usually click on a spot somewhere near the corner. In all cases you need the lat/lon of the location you intend to calibrate. How you get this number is up to you. Sometimes it can be taken from the map itself using a grid on the map, sometimes you can vist a spot such as a road intersection and use the gps to provide the lat/lon number for calibration. Sometimes you can compare the map on the palm with another map that has lat/lon data (perhaps palm based, perhaps pc based, or perhaps even a paper map) and transfer the data that way.

With only two points for calibration some assumptions must be made about the nature of the map. It is assumed to be orthoginal and the top is generally presumed to be north. It is presumed to be uniform scale over the whole map in the horizontal direction and in the vertical direction although the two directions do not have to be at the same scale. This precludes the use of a conic style projection.

Data is generally entered using the grafitti on the palm or the keyboard on the pc but in some cases you can set a waypoint using either manual entry or gps entry and use the waypoint as the calibration point.

I have seen one program that uses map center and scale to calibrate the map. This is generally less precise since it assumes the vertical and horizontal distances are the same and the scale is generally not precise enough to provide an accurate calibration but it may be valuable as a first step.

The instructions that comes with the programs explain the exact method used by that program. Generally it is useful to be able to adjust the numbers if you failed to get them exactly right the first time so the program should be able to display the existing calibration numbers so that you can change them. You will need to take note of the exact method of reporting and using the lat/lon numbers. It may be degrees and decimal parts of a degree or it may be degrees, minutes, and seconds. You will need to enter the data in the correct format. Conversion is pretty simple using a calculator but you need to realize which format the data you have is being displayed in and the format that you need.

Other Application Notes are being planned.

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Dale DePriest - all rights reserved.