Advanced Marksmanship App for measuring distance to target?

z7.jled

z7.jled

Sergeant of the Hide
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Minuteman
Feb 22, 2014
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Tampa, FL
#1
two part question:

first, how are the ELR folks measuring distance (like out to 6kyds)?

secondly, are there any apps that will work decently well to range out to about 1000. I know this is in the realm of many LRF's but I am saving up for a LRF right now, so I won't have it within the next month or two, but I will have an opportunity to do some shooting on private land with nearly unlimited distance and big ridges/cliffs/hills as a backstop. I have a few targets and would like to take a 66% IPSC out to about 1000-1200 yds and throw some lead at it. I could Mil the target for range, but there is some error there, so i'd like to use a gps based app to help me figure out a starting point, then mil the target and then shoot it and correct as needed.
 
#2
There is an app called "Measure Map" that can get you pretty close, provided you have cell service at your range

You basically pick two points on a map and it gives you the distance. Very easy to use.

Otherwise, Google Maps has a "measure distance" feature that you can access by right clicking on the point you want to measure in Google Maps.
 
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#5
Not sure about Google Earth measurements. For shooting it may not be an issue, since it is a relatively small distance (point to point). That being said, GE is not an accurate model for mensuration (precision geospatial measuring), since it's projection is based on a rough assumption that the earth is relatively round. It does not account for the fluctuation of the earth's crust and the ever changing shape of the planet (hence the need for Height Above Ellipsoid measurements, which in theory is the measurement of elevation based on the theoretical center of the earth, out to the surface, and accounts for the earth's position in orbit around the sun, as well as the lunar position; all which effects accurate three dimensional measurement). Probably way too in the weeds for ballistic applications, but I figured I'd toss it out as food for thought...
 
#8
MarinePMI said:
Not sure about Google Earth measurements. For shooting it may not be an issue, since it is a relatively small distance (point to point). That being said, GE is not an accurate model for mensuration (precision geospatial measuring), since it's projection is based on a rough assumption that the earth is relatively round. It does not account for the fluctuation of the earth's crust and the ever changing shape of the planet (hence the need for Height Above Ellipsoid measurements, which in theory is the measurement of elevation based on the theoretical center of the earth, out to the surface, and accounts for the earth's position in orbit around the sun, as well as the lunar position; all which effects accurate three dimensional measurement). Probably way too in the weeds for ballistic applications, but I figured I'd toss it out as food for thought...
Click to expand...
yeah way in the weeds, measuring “distance” on the surface of the earth can get weird for sure, I’m just wanting to get close enough for shooting,

I’ll play around with google earth/maps to see how “true” I can get it, I figure +\-30yds should get me a hit on a 20” target or at least close enough to spot the shot
 
#9
I use, Free Caddie Pro, and you can have a basic version that shows the distance to the middle of the green for free. Pay $1.99 and you get access to middle of the green, bunkers, water hazards, etc. Also lets you track strokes, measure shot distances, and has a disembodied voice that will tell you yardages (can be muted). Its not perfect, as there are a couple of holes where the GPS points for the front or back of the greens are a little off and the back of the green marker for #18 on my home course is off by about 40 yards, but with the map view you can quickly drag a marker to anywhere on the course and get a yardage. Of course as some have stated it is probably not allowed in competitions, but otherwise I've never been able to justify paying for a laser range finder while I generally can get it with a few yards my phone. Also, did I mention it's only $1.99.
 
#12
Distance Tool. It's a iPhone app. It's legit, ive checked it with many different known distances that I've encountered on jobs, and other known distances such as football fields, home plate to second base, mile sections. Just drop your pins and you have your yardage.
 
#14
I downloaded google earth, I'll try that tomorrow at the match.

what I am unsure of without trying it out is if I can drop a point (at a target for example) and then walk/drive a few hundred yards to a firing position and then measure the distance. land marks visible from a satellite are easy, but a random place in a field is more difficult to pick the right spot.
 
#15
z7.jled said:
I downloaded google earth, I'll try that tomorrow at the match.

what I am unsure of without trying it out is if I can drop a point (at a target for example) and then walk/drive a few hundred yards to a firing position and then measure the distance. land marks visible from a satellite are easy, but a random place in a field is more difficult to pick the right spot.
Click to expand...
You can with the Fields Area Measure app that uses Google data. At target drop pin, return to firing position save the data. You can then measure between the two pins. you can zoom in on the map and adjust either pin to get a more precise measurement. Tinker with it before your match it take a little time to figure out how to save add pins then measure, but the end result I find very good. I use it all the time now.
 
#17
z7.jled said:
yeah way in the weeds, measuring “distance” on the surface of the earth can get weird for sure, I’m just wanting to get close enough for shooting,

I’ll play around with google earth/maps to see how “true” I can get it, I figure +\-30yds should get me a hit on a 20” target or at least close enough to spot the shot
Click to expand...
I’ve toyed around with it once when I left my LRF at home like a moron...it ended up getting a little frustrating. First time I tried it worked but then it was all sorts of off when I tried to reach out further.
 
#18
It's likely due to the projection, and one of the points being on an adjacent tile. There will be some degree of "shear" between tiles, where geospatially they do not meet together correctly and a certain amount of fudge factor is added when distance is calculated across incongruous terrain tiles. Even on highly accurate, classified data models it occurs, but is over come by redundant coverage, as well as a rigorous math model that accounts for the shift/shear. It is why in some cases GE is fine, and in other cases...not so much. As long as your two end points are within a tile (and in a relatively flat area), it's fine (x/y, not z). The problem is that you can't visually see where one tile starts and another ends...

This is why geospatial measurements are done with multiple overhead data sources, and the sources' ephemeris data (legacy term) is used to calculate (via a sensor model) the known uncertainties of each data source, thereby spitting out a geocoordinate with associated accuracy projections for that specific point(s) on the image. In a pragmatic sense, the uncertainties of each source, helps cancel out the uncertainties of the other data sources (there's no magic here; garbage in, garbage out).

With GE you have a single source that has been fudged to make it (x/y) fit into the projection (versus retaining the errors, so that they can accurately be assessed, and addressed accordingly), and z (elevation) is just a guesstimate at best. I can't recall exactly how dense the post spacing is for the digital elevation model that GE uses (or if it is a grid or TIN; Triangular Irregular Network; which creates smaller facets), but seem to recall it being fairly course (100M post spacing?), which can add even more error to elevation. This means that in high relief areas (sharply changing terrain) distance errors will occur due to elevation rounding errors. These rounding errors occur when a point is selected between elevation posts within the terrain model, and the elevation is derived from a nearest-neighbor bipolar interpolation calculation (essentially rounding out the four nearest posts' values). If your point is located near a post (and not on it), the three other posts (that are much farther away from the point selected, and drastically different in elevation value) it will erroneously throw the average off. Add to that, if the elevation is off on each of the two points being used to calculate distance, the angle that is used to calculate distance will be skewed even more.

But I digress...

Buy an LRF. Problem solved.
 
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#19
ShtrRdy said:
Seems like there should be an app that uses GPS to get your location.

The YouTube "Mark and Sam after work" uses some some of measuring app on their phone.
Click to expand...
Distance tool does. I've checked it with many known distances that I've encountered on various jobs and it's stupid accurate.
 
#22
Coldbore has a GPS, Mapping and Targeting module, that among many other things let you measure distance to a target or clusters, it also features 72 ellipsoids to adjust to any map projection you can think of. A super cool and very powerful unmatched feature not found on any other package.
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