Global Positioning Systems

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Precision Lightweight GPS Receiver Q & A

1. If you wanted better locations, is there any software or capability to use these in a differential correction mode?

---------------- from Karl --------------- You can buy the SPS version, and apply classic differential, but you would lose the PPS advantages under canopy.

2. What accuracy are you comfortable is saying these units can achieve? In horizontal positions? Vertical positions?

---------------- from Karl --------------- IN the X and Y planes, 5-10 meters; Z is usually about 1.4 worse, say 7-14 meters

3. I am assuming that the mission planning software supplied with the units has satellite availability,etc for planning. Correct?

---------------- from Karl --------------- This is my understanding also.This is not correct. The military jargon of "Mission Planning" is tactical movement, download, reporting and displaying, etc. NOT "Pre-mission Planning" as the SPS world uses it. With a full constellation, looking at your 'windows' of coverage has become much less important, and in PPS operation, is not an issue of concern.

4. Do you have any direct knowledge of the use of geolink? I am pretty disappointed in the limits on the raster module (16 colors, 7.5 mb max image size). Also vector and raster map data seems to be limited to dumb backdrop status - no attributes are passed from the GIS software to geolink for use in the field - only linework. In an arc/info world it is just the information from an arc generate file, in a raster world it is a TIF or ERDAS file with no capability to identify categories (other than visually through the 16 colors supported).

---------------- from Karl --------------- I have a complimentary version right now. Without a receiver, I cannot test this issue presently. This is an excellent talking point for GeoResearch.

5. I am assuming that these units don't provide any additional capabilities to receive satellites that are low on the horizon or in topographically challenging terrain (steep). So we should have about the same luck using them as we do with conventional receivers. Is this correct? Are there any additional gotcha's associated with our northern latitudes and low angle satellites?

---------------- from Karl --------------- I understand the mask angle is (fixed) auto/adjustable on the PLGR. You are correct in this assumption; but I will inquire about northern latitude experiences and possible field adjustments.Mike Rasher has informed me that in testing the PLGR at northern latitudes, the receiver adjusts the mask angle down to 5 degrees as needed to obtain the necessary geometry for the required figure of merit (PDOP). The receiver does this automatically as needed.

6. From your perspective, what is the downside of the offer? Is there one?

---------------- from Karl --------------- Unknown / undocumented PLGR-Geolink capabilities, as you outlined above.

7. Will there be other chances to order these units this year? next year?

---------------- from Karl --------------- ** Mike and I are planning on a late 1995 buy, probably on FY96 money. It will not be for typical 1995 field season needs, though.

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