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#11
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What's the most accurate elevation tool on the net (freebie)
Jeff Liebermann wrote:
On Sat, 3 Mar 2012 18:47:56 -0000, wrote: GPS 3 meter error Yep. However, standing under the tower, in order to take advantage of this level of accuracy is often impractical. Climbing barbed wire topped chain link fences is not my idea of fun. I ran into the problem when I was throwing together a map of the local cell sites: http://802.11junk.com/cellular/ (from about 2002). I had a suitable GPS, but I couldn't get anywhere near some of the towers in order to get an accurate position. I had to record a GPS location nearby, measure or estimate the distance and direction to the tower, and then do the math. My objective was to determine my full Maidenhead before there were web applications to find it. I just took my portable, WAAS enabled, aviation GPS to the back yard and let it average for a couple of minutes. Since then I discovered why I kept getting different results pre-GPS (long boring story about map accuracies); turns out the dividing line runs down the sidewalk across the street. |
#13
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What's the most accurate elevation tool on the net (freebie)
Jeff Liebermann wrote:
On Sun, 4 Mar 2012 20:10:17 -0000, wrote: My objective was to determine my full Maidenhead before there were web applications to find it. Some GPS receivers will deliver the Maidenhead grid square directly. http://www.n7cfo.com/vhf/gps/~gps.htm I just took my portable, WAAS enabled, aviation GPS to the back yard and let it average for a couple of minutes. Since then I discovered why I kept getting different results pre-GPS (long boring story about map accuracies); turns out the dividing line runs down the sidewalk across the street. Chuckle. We're close to that problem at the local club station (K6BJ): http://802.11junk.com/jeffl/pics/drivel/slides/grid-cm8x.html I had to post this map because operators were constantly calculating the wrong grid square. Nearby, is the local intersection of the lat-long lines. http://confluence.org http://confluence.org/confluence.php?lat=37&lon=-122 Notice the wide variations in photos by people thinking they've found the correct location. The problem is that the real intersection is located on a poison oak infested steep hillside. We posted a DGPS located marker, but people keep stealing it. As it turns out, my house is in the very SW corner of DM14fco7, with the front in DM14fco7ae and the back in DM14fco7be. mandatory antenna content If you go to http://no.nonsense.ee/qthmap/ and enter DM14fco7be the white dot in the middle of the back yard is the box covering an SGC autotuner for the 33 foot vertical. |
#14
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What's the most accurate elevation tool on the net (freebie)
On Sat, 03 Mar 2012 19:43:47 -0800, Jeff Liebermann wrote:
What is the OP trying to accomplish? The neighbors and are discussing setting up a neighborhood mesh network and we need to ascertain, beforehand, where to place masts and which direction to point them in our mountainous neighborhood (Skyline & Summit area). If for an FCC license HAAT calculation, almost any reasonable guess will suffice. For us, probably any reasonable answer would suffice - but why not pick the most accurate for starters is what we're thinking. What level of accuracy is really required? The original position of 37.337408N -121.644073W is specified to 1 millionth of a degree, or about 0.09 meters. A few feet would probably work just fine for the neighborhood. We each have acres of land, but the terrain is so rough that only a few spots for antennas would be useful. That's why we want to choose them ahead of time. It would be interesting to know where this highly accurate number came from. We didn't want to put our actual location on the net, so, we picked an arbitrary set of numbers from one of the elevation calculators just as an example. But we're in the roughly 37,-122 range. What datum are you using? I suggest WGS84. WGS84. We have some numbers in NAD83 from the various WISP providers but they drive us crazy since we have to imperfectly convert them to WGS84 to keep our numbers consistent. Are you interested in ground level, building rooftop level, or tree top level? All three because we want to site a dozen or more antennas which need to have clear line of sight over rooftops and trees by at least the first Fresnel zone. |
#15
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What's the most accurate elevation tool on the net (freebie)
On Sat, 03 Mar 2012 19:43:47 -0800, Jeff Liebermann wrote:
http://www.maptools.com/UsingUTM/mapdatum.html Interesting quotes from that helpful reference (with my comments in parenthesis). "In the Continental United States the difference between WGS 84 and NAD 27 can be as much as 200 meters." (I wonder how they handle the constant creep which occurs out here near the San Andreas fault line). "Every map that shows a geographic coordinate system such as UTM or Latitude and Longitude with any precision will also list the datum used on the map." (I'd change "will" to 'should' based on my experience the past two weeks on the web) "The Global Positioning System uses an earth centered datum called the World Geodetic System 1984 or WGS 84." (That's what I prefer.) "For all practical purposes there is no difference between WGS 84 and NAD 83." (Good to know.) "On a USGS topographic map ... The datum will always be NAD 27... A dashed cross in the SW and NE corners of the map gives a visual indication of the difference between the two datums." (This is good to know.) "If you are engaged in a mission that requires more [than several hundred meters] precision, then your datums should match." (Since we're siting antennas on private hilly land, we probably want two or three meters accuracy in position and a half-meter to a meter in elevation accuracy so our datums must match.) |
#16
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What's the most accurate elevation tool on the net (freebie)
On Mon, 05 Mar 2012 15:30:57 +0000, alpha male wrote:
On Sat, 03 Mar 2012 19:43:47 -0800, Jeff Liebermann wrote: (I wonder how they handle the constant creep which occurs out here near the San Andreas fault line). What I mean by that is that it's a right-slip fault, and it moves by centimeters to inches each year (sometimes in feet to yards, both in elevation and in position) ... but ... how do they know if the west side moved north or if the east side moved south? I wonder what they use for their frame of reference since it depends on which side of the fault you're on if you want to say the west moved north or that the east moved south. |
#17
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What's the most accurate elevation tool on the net (freebie)
On Mon, 5 Mar 2012 15:09:40 +0000 (UTC), alpha male
wrote: On Sat, 03 Mar 2012 19:43:47 -0800, Jeff Liebermann wrote: What is the OP trying to accomplish? The neighbors and are discussing setting up a neighborhood mesh network and we need to ascertain, beforehand, where to place masts and which direction to point them in our mountainous neighborhood (Skyline & Summit area). Ok. Go thee unto: http://www.cplus.org/rmw/english1.html Follow the destructions at: http://www.cplus.org/rmw/download/download.php?S=1 For maps, download the SRTM3 maps for your area from: http://rmw.recordist.com Do not bother with DEM, SRTM1, or other maps. Do NOT unzip the maps. My directory shows about 600MBytes of SRTM3 data for everything for the SF Bay and Monterey Bay areas. You can set Radio-Mobile to automatically download a map if needed, but it's easier to just download the maps ahead of time. Follow a simple example such as: http://www.cplus.org/rmw/afirst.html to get started. There are also numerous tutorials on the web. Note that the program uses the concept of "networks" which will be key to modeling a mesh. Locate your nodes, use realistic values, and build a model. This part is a PITA and requires considerable time and effort. Draw the (optical) coverage areas for each node, and the line of sight: http://joelgranados.wordpress.com/2011/11/05/wireless-link-calculations-radio-mobile/ You're going to have a big problem in the Santa Cruz Mountains call trees. These are cellulose and water obstructions that may or may not appear at the correct altitude on the elevation profiles. 2.4GHz will NOT penetrate foliage, especially when wet. You'll need to manually adjust your path profiles for the tree line. If the trees are inside the Fresnel zone, you'll have losses. If you have problems, ask here, or preferably the Yahoo Radio-Mobile group at: http://groups.yahoo.com/group/Radio_Mobile_Deluxe/ I have a really bad attitude about mesh networks. Bug me if you want to hear the full rant. For a sample, see the dismal performance of an early mesh network (MIT Roofnet - Meraki). http://pdos.csail.mit.edu/roofnet/doku.php?id=interesting "Surprisingly, the performance over a two hop route is less than 1/2 that of one hop routes, implying routes tend to interfere with themselves." Also: http://sha.ddih.org/2011/11/26/why-wireless-mesh-networks-wont-save-us-from-censorship/ covers the main problems. Do you really want a phone call at 2AM from a neighbor asking if the network is down? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#18
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What's the most accurate elevation tool on the net (freebie)
On Sat, 03 Mar 2012 19:43:47 -0800, Jeff Liebermann wrote:
http://transition.fcc.gov/mb/audio/bickel/haat_calculator.html This is an interesting antenna HAAT (Height Above Average Terrain) program ... but I'm not quite sure what use it is because it gives a 360 degree average height ... but most 2.4Ghz antennas I'm dealing with are directional. You enter the latitude, longitude, & height of the antenna, and then it tells you, for example, for 360 degrees, the average antenna height above ground for 2 to 10 miles along each radial, the result of which can go negative. The output is a text file. It's interesting, but, without graphics, I'm not sure how to use the results properly when just going point to point. |
#19
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What's the most accurate elevation tool on the net (freebie)
On Mon, 5 Mar 2012 19:46:16 +0000 (UTC), alpha male
wrote: On Sat, 03 Mar 2012 19:43:47 -0800, Jeff Liebermann wrote: http://transition.fcc.gov/mb/audio/bickel/haat_calculator.html This is an interesting antenna HAAT (Height Above Average Terrain) program ... but I'm not quite sure what use it is because it gives a 360 degree average height ... but most 2.4Ghz antennas I'm dealing with are directional. You enter the latitude, longitude, & height of the antenna, and then it tells you, for example, for 360 degrees, the average antenna height above ground for 2 to 10 miles along each radial, the result of which can go negative. I wrote that before you disclosed what you were trying to accomplish. Had your intent to obtain accurate altitude readings been for the purpose of applying for an FCC station license, you would have needed the HAAT calculations to estimate coverage area. For building you mesh network, you don't need HAAT calculations. http://en.wikipedia.org/wiki/HAAT The first paragraph should explain what HAAT means. The output is a text file. It's interesting, but, without graphics, I'm not sure how to use the results properly when just going point to point. Hint: You can always take a table of number and create a graph or graphic. Going the other direction is not so easy. Most propagation and antenna design software generates an output table (text file), from which a graphic is later generated. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
#20
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What's the most accurate elevation tool on the net (freebie)
On 3/5/2012 8:26 AM, Jeff Liebermann wrote:
On Mon, 5 Mar 2012 15:09:40 +0000 (UTC), alpha male wrote: On Sat, 03 Mar 2012 19:43:47 -0800, Jeff Liebermann wrote: What is the OP trying to accomplish? The neighbors and are discussing setting up a neighborhood mesh network and we need to ascertain, beforehand, where to place masts and which direction to point them in our mountainous neighborhood (Skyline& Summit area). Ok. Go thee unto: http://www.cplus.org/rmw/english1.html Follow the destructions at: http://www.cplus.org/rmw/download/download.php?S=1 For maps, download the SRTM3 maps for your area from: http://rmw.recordist.com Do not bother with DEM, SRTM1, or other maps. Do NOT unzip the maps. My directory shows about 600MBytes of SRTM3 data for everything for the SF Bay and Monterey Bay areas. You can set Radio-Mobile to automatically download a map if needed, but it's easier to just download the maps ahead of time. Follow a simple example such as: http://www.cplus.org/rmw/afirst.html to get started. There are also numerous tutorials on the web. Note that the program uses the concept of "networks" which will be key to modeling a mesh. Locate your nodes, use realistic values, and build a model. This part is a PITA and requires considerable time and effort. Draw the (optical) coverage areas for each node, and the line of sight: http://joelgranados.wordpress.com/2011/11/05/wireless-link-calculations-radio-mobile/ You're going to have a big problem in the Santa Cruz Mountains call trees. These are cellulose and water obstructions that may or may not appear at the correct altitude on the elevation profiles. 2.4GHz will NOT penetrate foliage, especially when wet. You'll need to manually adjust your path profiles for the tree line. If the trees are inside the Fresnel zone, you'll have losses. If you have problems, ask here, or preferably the Yahoo Radio-Mobile group at: http://groups.yahoo.com/group/Radio_Mobile_Deluxe/ I have a really bad attitude about mesh networks. Bug me if you want to hear the full rant. For a sample, see the dismal performance of an early mesh network (MIT Roofnet - Meraki). http://pdos.csail.mit.edu/roofnet/doku.php?id=interesting "Surprisingly, the performance over a two hop route is less than 1/2 that of one hop routes, implying routes tend to interfere with themselves." Also: http://sha.ddih.org/2011/11/26/why-wireless-mesh-networks-wont-save-us-from-censorship/ covers the main problems. Do you really want a phone call at 2AM from a neighbor asking if the network is down? I've used Radio Mobile and SPLAT!. I never got a warm and fuzzy with Radio Mobile. Of course, it is a bit more complicated to use SPLAT!. One obvious advantage to SPLAT! is it can analyze very large areas. Not all that useful in the case of this wifi setup, but very useful in sigint. |
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