Big White Plusses??

[+CacheHord(e)]

When I was in California last year (near Sacramento) I noticed big white plus signs painted on the ground all over town. Some were on highways; some were on grassy fields. I guessed they were for aerial surveys, but does anyone on here know for sure?

 

I wish I had a picture to show you. They're about 2 feet wide and 2 feet high. Maybe a little more. Sometimes there's marker nailed in the center of the plus.

 

Team Hord

[iryshe]

Surveyors create them and sell them to imagery companies so they can match up their photos with the physical environment. They use these white x's (which have a bolt in the center), as well as street corners or any other highly visible structure that can be seen from the air.

 

If you want to be a full-time geocacher, this is one way to go I hear it pays pretty well too.

 

Jeremy Irish

Groundspeak - The Language of Location

[iryshe]

Surveyors create them and sell them to imagery companies so they can match up their photos with the physical environment. They use these white x's (which have a bolt in the center), as well as street corners or any other highly visible structure that can be seen from the air.

 

If you want to be a full-time geocacher, this is one way to go I hear it pays pretty well too.

 

Jeremy Irish

Groundspeak - The Language of Location

[+ca_surveyor]

The crosses are placed, as Jeremy says above, to provide ground control for aerial photography.

 

The crosses are placed, typically along some rough gridwork that the photogrammetry company defines based on the area to be mapped, the desired scale, and the altitude the plane will fly.

 

Given that, the surveyors will try to reach a point within about 50 feet of the target, establish a point, or use an existing monument, and then place a cross on the ground.

 

In the streets these are pretty simple. A can of cheap paint (so it doesn't last too long and blight the area and worse) and a brush. It gets more creative on a hillside or (my worst case, in a cow pasture..the cows kept eating the cross material).

 

I have heard of once case where the plane was early and the last cross was not done. The surveyor and his assistant lay on the ground and each pointed at the survey point.. it actually worked (but they had to keep doing it each time the plane went by because they never knew if they were in the grid line being currently photographed).

 

gil

ca_surveyor

 

(you got questions.. we got answers.. but do they match - grin)

[+CacheHord(e)]

Thanks for the authoritative reply. Are there any examples of these aerial photos I can see online? (Just curious)

 

Team Hord

[survey tech]

Landnetusa is a good source of various types of mapping including aerial photos.

[+n8aho]

Is there a technical name for this type of mark so I can search around on the web to find more information?

 

Jim

 

massillon ohio

 

stark county skywarn

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[+n8aho]

I found these this morning, could this be the same or similar to what the white plusses are for?

 

Jim

 

http://www.photolib.noaa.gov/historic/c&gs/thind8.htm

http://www.photolib.noaa.gov/historic/c&gs/theb0976.htm

http://www.photolib.noaa.gov/historic/c&gs/theb0977.htm

 

massillon ohio

 

stark county skywarn

packet radio, aprs

long haul 802.11b, warchalking

linux, os x

geocaching

geodashing

gps art

recumbent bikes

extreme kites

[+infosponge]

Yes, that's what they are.

 

quote:

---

Originally posted by n8aho:

I found these this morning, could this be the same or similar to what the white plusses are for?

Jim

---

[+makaio]

Like this one ? The benchmark is beneath the plate at the center of the cross.

 

The Data Sheet for this benchmark shows it's a HORIZONTAL marker which coincides with the aerial survey descriptions above.

 

-

[+EraSeek]

Here's one that is part of my ''Havesting The Tides'' cache: http://img.Groundspeak.com/cache/6596_200.jpg

 

a very cool spot!