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Messages - hwstock

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Map Making Support / Other sources of DEMs for Mexico
« on: June 07, 2013, 10:07:58 PM »
I've just used the USGS server to get 1 arc-second DEMS for Mexico. These work (with some reregistration), but I'd like at least 1/3 arc-second.

I just need fairly small areas-- like a 24k quad-worth.

Have you folks ever tried the commercially-available DEMs?  I'm guessing they are pricey. Examples:

Map Making Support / How to deal with x,y displacement
« on: June 07, 2013, 04:23:13 PM »
Howdy -- I've made a img (garmin) format map for an area of Baja, Mexico, in the bounds of 30 to 32 degrees north, 115 to 116 degrees west.  I used the process given in this site's tutorial (downloading data from the USGS NED server, converting gridfloat to geotiff via usgs and gdal utilities, stepping through Dem2topo, then gpsmapedit and cgpsmapper). I have some exact gps waypoints from the area, and can confirm that the countours are displaced approximately 200 feet west of the actual positions.

I assume that somewhere in the process, I can use obe of these clever programs to displace the contours 200' east, so they will coincide with the actual terrain.

Any idea where I would add this displacement (and how)?  It looks like the affine translation GPSMapEdit will work, but it looks bizarrely ungainly for my needs-- I really don't need 3 pair of points, I just need to displace the map in a well-known direction.  I don't want the imprecision of picking points off the map in GPSMapEdit.

I'm sure this error is real, because I previously bought the cartografia garmin-compatible maps for all of Mexico, and also looked over the competitors' garmin-compatible maps for that area.  Both were displaced by about 200'. I contacted the technical people at cartografia, and they confirmed the 200' displacement in that area, and were kind enough to fix the maps and send me the update.  However, I've found that some of the areas of interest for me in Mexico have similar displacements, probably due to some mismatch in datum or whatever. I'd like to make custom maps of those small areas, and correct them for the displacements.
EDIT: I figured out how to do it in GPSMapEdit -- pretty simple in the end.  Just make a gps file with 3 waypoints near edges (and not colinear!), and make 3 more that are displaced by the exact same amount.  Then add that gpx file to the project, and use the points to do the affine mapping by drag and drop. Worked like a charm.

General Discussion / Re: Transparency Problem
« on: October 31, 2012, 01:56:32 PM »
Fairly amusing.  I just reinstalled the utah, Arizona, Nevada, and California 24k maps-- now they are each indicated separately, whereas before they were lumped into one "Arizona USGS" set.  I have to disable NV to see the CA regions in CA near the border.

I "upgraded" to the latest BaseCamp yesterday-- now BaseCamp will absolutely NOT let me install the maps on the SD card (that's where they were before).  Every garmin upgrade, software or firmware, comes with new bombs that explode at random.

General Discussion / Re: Transparency Problem
« on: October 30, 2012, 10:27:01 AM »
I used BaseCamp to send the maps.  Actually, I just realized that the 2011 CalTopo maps have real top lines in the areas that overlap with NV and AZ-- it's the NV and AZ maps that cause the problems, so I'll be able to reload, and with luck, solve 80% of the problem.  Thanks for the info!

General Discussion / Re: Transparency Problem
« on: October 30, 2012, 09:46:02 AM »
I'm having a slightly related problem with my 62stc. There are built-in 100k maps for all states, and I've loaded AZ, CA and NV 24k topos.  On 62stc maps menu, the list shows the basemap, "Arizona Topos" (which actually seems to be all the 24k topos loaded from GPSfileDepot), the internal 100k maps, digital globe,  and "USGS Quads" (the last seems to be trail maps in 24k loaded from the Garmin national parks CD).

My problem is a bit ironic. The AZ, CA, and NV topos are 24k maps on a 100k grid, and each state has a grid block that extends across the border into the adjoining state.  Unfortunately, the NV border areas in the CA maps are blank, and the CA border areas in the NV maps are blank, and so on for AZ.  When all state 24k maps are loaded, the border regions are wiped out entirely.  Unfortunately these are some of the most interesting areas. If I disable "Arizona Topos" (which really has all the 24k topos), the underlying 100k grid shows through in this area.

There doesn't seem to be any way to get the overlapping maps to overlay "transparently."  The border 24k maps for CA wipe out the border 24k maps for NV, and so forth.


Any ideas?

Using The Maps/Garmin Software / Re: Error in maps for cebtral NV
« on: June 05, 2012, 08:32:12 AM »
Thanks much for your analysis!  The author of ExpertGPS found that many of the NV USGS topos off their web server were misregistered by about that amount.  Initially he had to apply the corrections before tying them in to his display. I guess the most you can do is keep a list of the quads that are off, leave it for folks to see (in the notes associated with the download), and communicate the error to the source of the DEMs.

Using The Maps/Garmin Software / Re: Error in maps for cebtral NV
« on: June 04, 2012, 01:02:00 PM »
?? The 24k map contours are shifted east by several hundred feet.  The "road" is NOT a road at all, but is a track recorded on my gps, as I was walking/climbing.  The track plots correctly on USGS (via expert GPS), memmap, and Maptech software.  It plots incorrectly on the 24k NV maps available on this site.  I was there; I traveled directly up the ridge, and did not sidehill  for miles. I get this on 2 gps units that have the 24k maps from this site. Your 24k maps have proved to be "on" in many, many other NV locations.  But they are out-of-whack here.

Using The Maps/Garmin Software / Re: Error in maps for cebtral NV
« on: June 01, 2012, 04:28:56 PM »
Those are two of them... but enough to show the error.  The other two files (that I tried to link) just verify that 2 other sources give the correct placement of the track (i.e., a different placement than the NV 24k maps on this site).

I can do a search out from Desatoya Twins, by putting waypoints on peaks in mapping software, then plotting those waypoints on the NV 24k maps from GPSFileDepot, if that might help.  Then I could binary search in to try to locate the border between right and wrong maps... may be more tedious than I imagine, especially in flat areas.

Using The Maps/Garmin Software / Error in maps for cebtral NV
« on: June 01, 2012, 01:34:23 PM »
The recommended NV 24k maps have a registration error for one region of central NV near the Desatoya Twins (east of route 50, WSW of Austin).

I'd like to show you exactly where, but this brain-dead BBS software will not allow me to post external links

This looks like a datum error when the contour map was created from the DEM.  I have used the NV 24k maps in many parts of Nevada, and this is the 1st error that I have seen.

E-mail me if you want to undeniable examples of the error.

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