Dan Anderson

GPS Expert
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About Dan Anderson

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    http://www.gpsmap.net
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  • Location
    Colorado
  1. There are measurement errors and there is data that was simplified so boundaries are approximate - lines that twist and turn become straighter. I've been trying to put in boundaries of some private property "correctly" on a map. The county GIS has multiple overlays that don't agree. The Forest Service map and topo map show a city park boundary ending on an 1/8 section boundary. That is where the boundary should have been but a surveyor made a mistake. The community is actually around 200 feet to the west and south of where it should have been (based on section monuments). I took information from one of the county GIS overlays and went looking for survey monuments associated with the private property. Found one and some debris at another corner may have been from an old fence line. There is also an entry gate that fits the actual boundary plus some t-bars at another location that seem to match the expected boundary line. The Forest Service has had some survey teams re-doing their boundaries around here. They were about to put in boundary signs that put the community partly on Forest Service land. I asked if they knew of the survey monument I found. They didn't and I showed them where it is. That survey seems to be on hold - signs are not being added. There are a couple of other locations in this region where mistakes were made (steep hillsides made for difficult measurements). Some section lines were run WNW instead of West (significant error). The maps assume the lines ran East/West so the boundaries on the maps are wrong. Another section line running North/South was surveyed a while ago (maybe '70's - it's been a year since I read it) with survey monuments added. The recent team must have spent more time looking and found the original (or earlier survey markers). They marked some of the later monuments (from the 70's) as incorrect and added correct ones at the original locations.
  2. Thanks Carl for pointing out the rules. Looking up the PLSS standards, one of the adjustments to put a square grid on the curved surface of the Earth is to cut down the size of the northern and western sections (numbers 1 to 7, 18, 19, 30, and 31). So one mile is measured from the SE corner for the first five sections and the sixth is short changed. For subdividing sections, I checked one map from the BLM for the area I am looking at and the subdivision lines of sections are equally spaced. If Colorado has some rule about measuring from the SE corner of a section, it wasn't applied in that area.
  3. A couple of other methods to try... I generally draw a selection box around the points I want to delete (they are marked in pink). I might do this a few times to avoid selecting the points I don't want to delete. Sometimes it helps to reverse the track due to the sequence the trackpoints are selected. When the selection box doesn't work very well (can't avoid selecting points you don't want to delete and can't select enough at once that you do want to delete), I try using the "marker". Select track - put pointer over track at point you want to start deleting - hold left mouse botton down and move slightly to get marker tool - drag over track and not necessarily following track (move directly to another part and all points inbetween will be selected) - delete selected points. You may want to delete two adjacent points created at the "cut" points of the marker. Be careful that you don't select the part of the track that you don't want to delete if you move the marker tool directly to another area of the track. Sometimes the selection will change to a different direction depending on your track layout. "Simplify" track may also help depending on how much resolution you want. I believe "Simplify" only works on the whole track. It might be useful if "Simplify" would only process the pink highlighted section of a track or the whole track if there is no highlighted section.
  4. As Carl suggested - perhaps putting the cumulative distance as the waypoint name with some prefix. I'm wondering about the case when there is no trackpoint within a reasonable distance of the interval desired. In other words, you want the 1 mile point but the nearest trackpoints are .25 miles on either side. Somewhat related - dividing up a track into desired intervals - add trackpoints in between other points at desired distance if a trackpoint doesn't already exist. This would also help with one of the chores I had to do recently - dividing sections up into quarters and eighths in an area where the section lines were not all parallel (at least on the topo map).
  5. What is the filename extension on the files you tried to post? I would expect the files to have the extension ".gpx".
  6. Is the magnetic north reference setup to give the current value at the given location?
  7. It might help if you post one of the files that displays correctly and the modified file that does not display correctly. Select "More Reply Options" or "Use Full Editor" to get an Attach Files option with a Browse button.
  8. Yes, the "ACTIVE LOG" is the true record of the route you followed with all the data.
  9. My guess is that the route distance includes the elevation of the waypoints so it could be a 3D distance. The active point may not have an elevation value, so the distance from it to waypoints would be a 2D distance.
  10. The ACTIVE LOG is the track recorded by the receiver based on your track log settings. The track "18-OCT-13" is a "saved" log that the receiver creates from the current ACTIVE LOG. The ACTIVE LOG is not saved as you might expect but is simplified and stored. Time stamps on the track points no longer represent the actual speed from point A to point B because the distance may be different so the time stamps are removed.
  11. You have the coordinates of the center of the circles and the radii so you need to solve the equations of the two circles which gives you the intersection coordinates. Note that the units should all be the same. If you are using state plane coordinates in feet and the radii are in the state plane feet, then you are good to go. If you are using UTM in meters then convert the radii to meters. Center of circle = a, b Equation of circle = (x-a)^2 + (y-b )^2 = r^2 or ("^" = raised to power) x^2 + y^2 - 2ax - 2by + a^2 + b^2 - r^2 = 0 also if ax^2 + bx + c = 0 then x = (-b + SQRT(b^2 - 4ac))/2a and x = (-b - SQRT(b^2 - 4ac))/2a Example: Two circles at a,b = 1000, 1200 r = 200 and a,b = 1100, 1300 r = 300 Equation of circle 1: x^2 + y^2 - 2000x - 2400y + 1,000,000 + 1,440,000 - 40,000 = 0 Equation of circle 2: x^2 + y^2 - 2200x - 2600y + 1,210,000 + 1,690,000 - 90,000 = 0 Solving the two equations gives the points of intersection of the two circles. x^2 + y^2 - 2000x - 2400y + 2,400,000 = x^2 + y^2 - 2200x - 2600y + 2,810,000 Reduces to... -2000x - 2400y = -2200x - 2600y + 410,000 and 200x + 200y = 410,000 or y = 2050 - x Substituting for y in equation 1... x^2 + (2050-x)^2 - 2000x - 2400(2050-x) + 2,400,000 = 0 or 2x^2 - 6100x + 4,202,500 - 4,920,000 + 2400x + 2,400,000 = 0 reduces to... x^2 - 1850x + 841,250 = 0 In the quadratic equation above a=1, b=-1850, c=841250 x = (1850 + SQRT( 1850*1850 - 4*841250)) / 2 = 1044.9 y = 2050 - x = 1005.1 and x = (1850 - SQRT( 1850*1850 - 4*841250)) / 2 = 805.1 y = 2050 - x = 1244.9 So the circles intersect at 1044.9, 1005.1 and 805.1, 1244.9 Note that this assumes a plane (flat) surface. As the radius becomes larger, it will get more inaccurate.
  12. A file (such as a GPX format file) containing trackpoints can be generated by a computer, so an insurance company should be cautious in taking it as evidence. On old Garmin receivers, a tracklog uploaded to the receiver had some data removed, so when you downloaded tracklogs from the receiver, you could tell what was uploaded and what was generated by the receiver. Someone at an insurance company could download the data from a receiver and have more confidence that the data was not modified.
  13. Hi Dan, After your post, I mapped out 7 areas at 6 zoom levels that were all black. Two days later when I went to continue checking all those black areas had been replaced by aerial photos. I don't know of any black areas at this time. Today I ran into three areas where there are no topo maps at zoom 14. I've attached a gpx file for those areas. Maybe they'll be okay shortly too. If not, can a different server be used for topo maps?
  14. In my area, some of it is covered by high resolution aerial photos. Some of the border areas are black then there is no adjacent aerial photos at a high resolution. So as you pan through the aerial photos you can hit a wide, black border then no imagery. I think I've seen black to white then nothing too. The government just hasn't supplied the data.
  15. It sounds like you are asking for a file server. You can specify who can upload to the server and who can download from the server. EasyGPS is a program (application) that edits those files. It is not a file server.